Patent Publication Number: US-2021189643-A1

Title: Foam dyeing methods using modified indigo compounds

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/608,951 filed Dec. 21, 2017, which is incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to methods of foam or spray dyeing substrates using modified indigo compounds. 
     BACKGROUND 
     Foam dyeing is a technique where a uniform dispersion of foam (air in water) are applied onto substrate. This technique can be used to deliver dyestuff, sizing, and various treating chemicals in a controlled manner. To obtain a uniform distribution and to obtain desired penetration, the foam is normally applied under pressure. A key benefit of this technique is the significant reduction in water usage, waste water generation and reduction in energy when the fabric is dried. 
     Indigo is insoluble in water. Reduction of indigo to leuco-indigo and increased pH (&gt;10) leads to increased solubility in the absence of oxygen. A key challenge is to maintain oxygen content at very low levels (ppm) to ensure consistent delivery of leuco-indigo onto substrate. This is done by introducing nitrogen (and or other inert gases) into the dyeing chamber which is hermetically sealed. Any oxygen leak into the chamber would cause significant variability in dyeing. 
     What is needed are foam dyeing techniques using indigo dyes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present application is further understood when read in conjunction with the appended drawings. For the purpose of illustrating the subject matter, these are shown in the drawings exemplary embodiments of the subject matter; however, the presently disclosed subject matter is not limited to the specific compositions, methods, devices, and systems disclosed. In addition, the drawings are not necessarily drawn to scale. 
         FIG. 1  is an image of white 100% polyester pants sprayed using a 6% Compound 8 aqueous solution containing 5% thickener. 
         FIG. 2  is an image of white 100% cotton jacket sprayed using a 6% Compound 8 aqueous solution containing 5% thickener. A resist was used to maintain the pattern and mask deposition of Compound 8. 
         FIG. 3  is an image of denim pants sprayed using a 6% Compound 8 aqueous solution containing 5% thickener. 
         FIG. 4  is an image of a denim jacket sprayed using a 6% Compound 8 aqueous solution containing 5% thickener. 
     
    
    
     SUMMARY 
     The disclosure provides methods of foam or spray dyeing a substrate, comprising contacting the substrate with a foam or a spray that comprises a dye compound comprising an indigo derivative, or a salt thereof, having one or more modification over the chemical structure of indigo, wherein the indigo derivative has a water-solubility of greater than 0.2% w/v in the absence of a reducing agent and in the presence oxygen, and converts to indigo upon removing the modification. In some embodiments, the foam comprises air. In other embodiments, the foam contains at least about 10% of oxygen. In further embodiments, the spray comprises about 60 to about 95 wt. %, based on the weight of the spray, of water. In yet other embodiments, the dye compound is of Formula (I) or (II), wherein R 1 -R 4 , R 7 , R 8 , m, and n are defined herein. 
     
       
         
         
             
             
         
       
     
     The disclosure also provides dyed substrates prepared according to the methods described herein. 
     The disclosure further provides sprays for dyeing a substrate, the spray comprising water and a dye compound comprising an indigo derivative, or a salt thereof, having one or more modification over the chemical structure of indigo, wherein the indigo derivative has a water-solubility of greater than 0.2% w/v in the absence of a reducing agent and in the presence oxygen, and converts to indigo upon removing the modification. 
     The disclosure additionally provides foams for dyeing a substrate, comprising air and a dye compound comprising an indigo derivative, or a salt thereof, having one or more modification over the chemical structure of indigo, wherein the indigo derivative has a water-solubility of greater than 0.2% w/v in the absence of a reducing agent and in the presence oxygen, and converts to indigo upon removing the modification. In some embodiments, the foam comprises at least about 10 wt. %, based on the total weight of the foam, of oxygen. 
     Other aspects and embodiments of the invention will be readily apparent from the following detailed description of the invention. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Embodiments of the present disclosure are directed to improved foam or spray dyeing substrate, such as cotton yarn, using a modified indigo compound in place of leuco-indigo. This process provides a number of benefits over conventional indigo dyeing methods. For instance, in contrast with leuco-indigo, the modified indigo compound is stable in the presence of oxygen. Accordingly, contact with atmospheric oxygen will not cause the modified indigo compound to convert to indigo. As such, the modified indigo compound is suitable for dyeing a yarn using conventional foam or spray dyeing processes without protecting the dye from contact with atmospheric oxygen, such as through the use of reducing agents or the like. 
     The inventors found that a modification of indigo or leuco-indigo could increase its affinity for the cotton and potentially eliminate the need for one or more of the use of reducing agents in the foams or sprays, or the need to sky the yarn. Preferably, this modification is environmentally friendly and atom efficient. It also is quickly and completely removable when exposed to a simple reagent or condition in order to leave standard indigo on the yarn. 
     Accordingly, the foam and spray dyeing processes of the present disclosure may be performed without the need for reducing agents in the foams or sprays. As such, the amount of reducing agents in the dye solution may be significantly decreased or, more preferably, the reducing agents may be eliminated from the dye solution altogether. 
     The oxygen stability of the modified indigo compound also renders it highly advantageous for foam and spray dyeing processes, in which the dye comes into substantial contact with the atmosphere in which the process is performed. In part because of the instability of leuco-indigo in air, the foam dyeing of textile yarns with indigo has yet to be commercially developed. This is, at least in part, due to the large amounts of an inert gas that are required in order to apply a foam containing leuco-indigo to a yarn. In contrast, the modified indigo compounds may be applied to textile yarns through a foam dyeing process that takes place in air, i.e. without the need for an inert gas environment. 
     Because the modified indigo compounds of the present disclosure tend to convert to indigo through hydrolysis, contact with water may cause the modified indigo compounds of the present disclosure to begin to convert into water-insoluble indigo. Since the dyeing process preferably comprises contacting the yarn with an aqueous solution containing the modified indigo compound, stability of the modified indigo compound in aqueous solution is important commercially (e.g. for maintenance of a dye composition). Notably, the modified indigo compounds of the present disclosure are capable of remaining in aqueous solution for a commercially significant amount of time before substantial conversion to indigo occurs. 
     In some embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution (at room temperature) for a period of at least five minutes before substantial conversion to water-insoluble indigo occurs. In other embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least ten minutes before substantial conversion to water-insoluble indigo occurs. In further embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least thirty minutes before substantial conversion to the water-insoluble indigo compound occurs. In yet other embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least one hour before substantial conversion to water-insoluble indigo occurs. In still further embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least three hours before substantial conversion to water-insoluble indigo occurs. In other embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least ten hours before substantial conversion to water-insoluble indigo occurs. In further embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least fifteen hours before substantial conversion to water-insoluble indigo occurs. In yet other embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least twenty hours before substantial conversion to water-insoluble indigo occurs. In still further embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least one day before substantial conversion to water-insoluble indigo occurs. In other embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least one and one-half days before substantial conversion to water-insoluble indigo occurs. In further embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least two days before substantial conversion to water-insoluble indigo occurs. In still other embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least three days before substantial conversion to water-insoluble indigo occurs. In yet further embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least five days before substantial conversion to water-insoluble indigo occurs. In other embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least one week before substantial conversion to water-insoluble indigo occurs. In further embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least ten days before substantial conversion to water-insoluble indigo occurs. In still further embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least two weeks before substantial conversion to water-insoluble indigo occurs. In yet other embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least three weeks before substantial conversion to water-insoluble indigo occurs. In further embodiments, the modified indigo compounds of the present disclosure remain in aqueous solution for a period of at least one month (i.e. 30 days) before substantial conversion to water-insoluble indigo occurs. 
     The modified indigo compound may also have improved water solubility relative to conventional leuco-indigo. 
     The modified indigo compounds of the present disclosure also have increased water solubility when compared to leuco-indigo. Accordingly, dyeing yarns with the modified indigo compound provides a process in which more indigo dye can be placed on the yarn per period of contact relative to conventional dyeing methods. Moreover, one may obtain a darker indigo dye using a relatively lower contact time than would be necessary using a conventional leuco-indigo dye composition. In some embodiments, for example, the concentration of the modified indigo compound in an aqueous dye solution may be at least 0.3 wt. %, at least 0.5 wt. %, at least 0.6 wt. %, at least 0.8 wt. %, at least 1 wt. %, at least 2 wt. %, at least 3 wt. %, at least 5 wt. %, at least 10 wt. %, at least 15 wt. %, or at least 20 wt. %. 
     The improved water solubility of the modified indigo compounds of the present disclosure also simplifies the process by which the dye foam or spray is controlled, and, more particularly, by which the modified indigo compound is maintained at a substantially constant concentration within the dye foam or spray. This, in turn, minimizes the inclusion of additional chemicals, which leads to decreased costs and a lower environmental impact. 
     As described above, the modified indigo compounds disclosed herein have a beneficial combination of (a) greater oxygen stability than leuco-indigo (such as may be measured at room temperature) and (b) greater water solubility than leuco-indigo (such as may be measured at room temperature). In some embodiments, the modified indigo compounds may further have (c) greater affinity to cotton than leuco-indigo. 
     In the present disclosure the singular forms “a”, “an” and “the” include the plural reference, and reference to a particular numerical value includes at least that particular value, unless the context clearly indicates otherwise. Thus, for example, a reference to “a material” is a reference to at least one of such materials and equivalents thereof known to those skilled in the art, and so forth. 
     When a value is expressed as an approximation by use of the descriptor “about” or “substantially” it will be understood that the particular value forms another embodiment. In general, use of the term “about” or “substantially” indicates approximations that can vary depending on the desired properties sought to be obtained by the disclosed subject matter and is to be interpreted in the specific context in which it is used, based on its function. The person skilled in the art will be able to interpret this as a matter of routine. In some cases, the number of significant figures used for a particular value may be one non-limiting method of determining the extent of the word “about” or “substantially”. In other cases, the gradations used in a series of values may be used to determine the intended range available to the term “about” or “substantially” for each value. Where present, all ranges are inclusive and combinable. That is, references to values stated in ranges include every value within that range. 
     When a list is presented, unless stated otherwise, it is to be understood that each individual element of that list and every combination of that list is to be interpreted as a separate embodiment. For example, a list of embodiments presented as “A, B, or C” is to be interpreted as including the embodiments, “A,” “B,” “C,” “A or B,” “A or C,” “B or C,” or “A, B, or C.” 
     It is to be appreciated that certain features of the invention which are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. That is, unless obviously incompatible or excluded, each individual embodiment is deemed to be combinable with any other embodiment(s) and such a combination is considered to be another embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub-combination. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. Finally, while an embodiment may be described as part of a series of steps or part of a more general structure, each said step may also be considered an independent embodiment in itself. 
     I. THE COMPOUNDS 
     In solving the problems in the art, the inventors developed modified dye molecules that are likely to bond more strongly to cotton than in the current dyeing process, are soluble in water, can be converted to indigo in one simple step after dyeing, are cost effective or provide a cost saving over the current process, more stable than leuco-indigo, and/or readily dissolves in water, unlike standard, indigo, and readily converts back to indigo quickly and easily without skying. 
     Furthermore, core dyeing of yarn with the modified dye molecule is possible and controllable; there is a large reduction in production water and waste water; there is a reduction in the chemicals required for the process; the molecule, auxiliary chemistries, and effluent are likely to be suitable for standard wastewater treatment processes; the modification is introduced to indigo in a few simple steps, and is stable; the molecule could be supplied to dye houses in its modified form; and no reducing agents are required. Such benefits can be gleaned using all forms of dyeing, including those discussed below. 
     The present disclosure provides dye compounds for use in dyeing substrates. The dye compounds comprise an indigo derivative, or a salt thereof, having one or more modification over the chemical structure of indigo. The inventors found that these compounds convert to indigo via hydrolysis. In some embodiments, hydrolysis is accomplished using a hydrolyzing agent, heat, steam, or combinations thereof. Advantageously, these compounds were found to be substantially stable in the presence of an oxidant such as in aqueous solutions, which property is not shared with leuco-indigo. Preferably, the compounds were found to be substantially stable in the presence of oxygen. These compounds were also found to be more stable in the air than other indigo derivatives such as leuco-indigo. 
     The term “substantially stable” refers to the ability of the compound to maintain its structure and properties thereof. In some embodiments, a compound&#39;s stability is maintained without being reduced, oxidized, or reacting with another component of the foam or spray or method discussed herein. In other embodiments, the compound is stable since it maintains its water solubility. In further embodiments, the compound is stable since it does not convert to indigo. Desirably, less than about 50 wt. %, such as less than about 45, less than about 40, less than about 35, less than about 30, less than about 25, less than about 20, less than about 15, less than about 10, or less than about 5 wt. % of the compound in an aqueous solution degrades under atmospheric conditions over a period of about 12 hours in the absence of a reducing agent. Degradation can be measured using any analytical technique which is capable of quantifying a chemical compound including, without limitation, gas chromatography, UV-visible spectrophotometry, nuclear magnetic resonance, mass spectroscopy, or combinations thereof. In some embodiments, about 0.001 to about 50 wt. % of the compound, about 0.001 to about 45, about 0.001 to about 40, about 0.001 to about 35, about 0.001 to about 30, about 0.001 to about 25, about 0.001 to about 20, about 0.001 to about 15, about 0.001 to about 10, or about 0.001 to about 5 wt. % of the compound in an aqueous solution degrades under atmospheric conditions over a period of about 12 hours in the absence of a reducing agent. In further embodiments, 0.001 to about 5 wt. % of the compound in an aqueous solution degrades under atmospheric conditions over a period of about 12 hours in the absence of a reducing agent. 
     The inventors also found that the compounds described herein have greater water solubility than indigo. In some embodiments, the dye compounds have a water solubility of about 0.2% w/v or greater. In preferred embodiments, the water solubility is about 0.2% w/v or greater in the absence of a reducing agent. In other preferred embodiments, the water solubility is about 0.2% w/v or greater in the presence of oxygen. In yet further embodiments, the water solubility is about 10 to about 100%, about 20 to about 100, about 30 to about 100, about 40 to about 100, about 50 to about 100, about 60 to about 100, about 70 to about 100, about 80 to about 100, about 90 to about 100, about 95 to about 100, about 98 to about 100, about 99 to about 100, or about 100 w//v. The water solubility of the compounds described herein may be measured using techniques known to those skilled in the art including, without limitation, dissolution with agitation, followed by filtration of centrifugation to isolate the soluble solids. The insoluble solids are then dried and weighed and the solubility calculated. 
     The term “indigo” as used herein refers to the following compound. 
     
       
         
         
             
             
         
       
     
     Similarly, the term “leuco-indigo” is used interchangeably with “indigo white” and refers to the following compound. In some embodiments, leuco-indigo exists in the neutral form. 
     
       
         
         
             
             
         
       
     
     Leuco-indigo may also exist in a deprotonated form, such as a form which is deprotonated on one or both oxygen atoms. Thus, the term “leuco-indigo” can include the mono-anionic and di-anionic forms including the monosodium, monopotassium, monolithium, disodium, dipotassium, or dilithium analogs of the following: 
     
       
         
         
             
             
         
       
     
     Thus, the one or more modification is designed to enhance the aqueous solubility of the dye derivative lacking the modification. The term, “enhance” as used herein refers to improving the solubility to the dye derivative lacking the modification, improving the affinity of the indigo compound to a substrate, as defined herein, providing an indigo compound that converts to indigo upon removing the modification, or combinations thereof. In some embodiments, the modification is removed by hydrolysis. 
     In some embodiments, the modification enhances the aqueous water-solubility of the indigo derivative. The modification is made at any position on the indigo backbone or the indigo derivative. In some embodiments, one or more modification is a substituent on indigo or the indigo derivative. In other embodiments, the substituent is on one or more carbon atom. In further embodiments, the substituent is on one or both nitrogen atom. In yet other embodiments, the substituent is on one or both oxygen atoms. The modification may be selected by one skilled in the art and includes, without limitation, acyl, alkyl, alkoxy, amide, amine, anhydride, aryl, carbamate, CN, cycloalkyl, ester, halide, heteroaryl, heterocyclyl, imine, mesylate, NO 2 , oxime, sulfonate, tosylate, or urea, wherein each substituent is optionally substituted. In some embodiments, the modification results in an indigo compound which is rotationally symmetrical about an axis. In other embodiments, the modification results in an indigo compound which is rotationally asymmetrical about an axis. However, the modification results in a dye compound that is not the methylsulfonate salt of (E)-3,3′-(3,3′-dioxo-[2,2′-biindoline-1,1′-diyl]-1,1′-dicarbonyl)bis(1-methylpyridin-1-ium). 
     The term “wt. %” or “weight %” as used herein refers to the weight of the referenced compound based on the total weight of the solution. For example, the amount of Compound A in an aqueous solution contain 0.01 wt. % of Compound A is based on the based on the total weight of the components in the aqueous solution. 
     The term “alkyl” is used herein to refer to both straight- and branched-chain saturated aliphatic hydrocarbon groups. In one embodiment, an alkyl group has 1 to about 10 carbon atoms, i.e., C 1-10 alkyl. In another embodiment, an alkyl group has 1 to about 6 carbon atoms, i.e., C 1-6 alkyl. In a further embodiment, an alkyl group has 1 to about 4 carbon atoms, i.e., C1-4alkyl. The alkyl may be unsubstituted or substituted as described herein. The substitution may be on any carbon-atom, as permitted by the stability and valency of the substituent. In some examples, the alkyl is a methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, or decyl. 
     The term “alkoxy” as used herein refers to the O-(alkyl) group, where the point of attachment is through the oxygen-atom and the alkyl group is defined above. In some examples, the alkyl is a methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, octoxy, nonoxy, or decoxy. 
     “Ester” refers to a —COOR group and is bound through the C-atom. R includes, but is not limited to, alkyl, cycloalkyl, aryl, heteroaryl, or heterocyclyl. 
     “Acyl” refers to a —C(O)R group which is bound through the C-atom. R includes, but is not limited to, alkyl, cycloalkyl, aryl, heteroaryl, or heterocyclyl. 
     “Carboxyl” refers to a —C(O)OH group which is bound through the C-atom. 
     “Amine” refers to —NH 2 , —NHR, or —NR 2  which is bound through the N-atom. Each R, independently, includes, but is not limited to, alkyl, cycloalkyl, aryl, heteroaryl, or heterocyclyl. 
     “Amide” refers to a —C(O)NR 2  group which is bound through the C-atom. Each R, independently, includes, but is not limited to, H, alkyl, cycloalkyl, aryl, heteroaryl, or heterocyclyl. 
     “Sulfate” refers to a —SO 3 R group which is bound through the S-atom. Each R includes, but is not limited to, H, alkyl, cycloalkyl, aryl, heteroaryl, or heterocyclyl. 
     “Sulfonate” refers to a —SO 2 R group which is bound through the S-atom. Each R includes, but is not limited to, H, alkyl, cycloalkyl, aryl, heteroaryl, or heterocyclyl. 
     “Carbamate” refers to a —OC(O)NR 2  group which is bound through the O-atom. Each R, independently, includes, but is not limited to, H, alkyl, cycloalkyl, aryl, heteroaryl, or heterocyclyl. 
     “Urea” refers to a —NRC(O)NR 2  group which is bound through the N-atom. Each R, independently, includes, but is not limited to, H, alkyl, cycloalkyl, aryl, heteroaryl, or heterocyclyl. 
     “Imine” refers to a —C(R)═NR group which is bound through the C-atom. R includes, but is not limited to, H, alkyl, cycloalkyl, aryl, heteroaryl, or heterocyclyl. 
     “Oxime” refers to a —C(R)═NOH group which is bound through the C-atom. R includes, but is not limited to, H, alkyl, cycloalkyl, aryl, heteroaryl, or heterocyclyl. 
     “Thioether” refers to a —SR group which is bound through the C-atom. R includes, but is not limited to, H, alkyl, cycloalkyl, aryl, heteroaryl, or heterocyclyl. 
     “Anhydride” refers to a —C(O)OC(O)R which is bound through the C-atom. R includes, but is not limited to, H, alkyl, cycloalkyl, aryl, heteroaryl, or heterocyclyl. 
     The term “halogen” are “halide” are used interchangeably and refer to Cl, Br, F, or I groups. 
     “Cycloalkyl” refers to a monocyclic or polycyclic radical that contains carbon and hydrogen, and may be saturated or partially unsaturated. In some embodiments, cycloalkyl groups include 3 to about 12 ring atoms, i.e., C3-12cycloalkyl. In other embodiments, cycloalkyl groups include 3 to about 8 ring atoms, i.e., C3-cycloalkyl. In further embodiments, cycloalkyl groups include 5 to about 7 ring atoms, i.e., C5-7cycloalkyl. Examples of cycloalkyl groups include, but are not limited to cyclopropyl, cyclobutyl, cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, norbornyl, and the like. The cycloalkyl may be unsubstituted or substituted as described herein. The substitution may be on any carbon-atom, as permitted by the stability and valency of the substituent. 
     “Heterocyclyl” refers to a saturated ring that comprises 3 to 12 carbon atom, i.e., C3-12heterocyclyl, and from 1 to 6 heteroatoms which are nitrogen, oxygen or sulfur. The heterocyclyl is a monocyclic, bicyclic, tricyclic or tetracyclic ring, which may include fused or bridged ring systems. The heteroatoms in the heterocyclyl may be optionally oxidized. The heterocyclyl may be attached to the rest of the molecule through any atom of the ring(s). In some embodiments, the heterocyclyl has 3 to about 18 ring atoms. In some embodiments, heterocyclyl groups include 4 to about 8 ring atoms. In other embodiments, heterocyclyl groups include 5 to about 7 ring atoms. In some preferred embodiments, the heterocyclyl includes, but are not limited to, dioxolanyl, thienyl[1,3]dithianyl, decahydroisoquinolyl, imidazolinyl, imidazolidinyl, isothiazolidinyl, isoxazolidinyl, morpholinyl, octahydroindolyl, octahydroisoindolyl, 2-oxopiperazinyl, 2-oxopiperidinyl, 2-oxopyrrolidinyl, oxazolidinyl, piperidinyl, piperazinyl, 4-piperidonyl, pyrrolidinyl, pyrazolidinyl, quinuclidinyl, thiazolidinyl, tetrahydrofuryl, trithianyl, monosaccharidyl such as tetrahydropyranyl (glucose), thiomorpholinyl, thiamorpholinyl, 1-oxo-thiomorpholinyl, and 1,1-dioxo-thiomorpholinyl. The heterocyclyl may be unsubstituted or substituted as described herein. The substitution may be on a carbon-atom or heteroatom, as permitted by the stability and valency of the substituent. 
     The term “aryl” refers to 6-15 membered monocyclic, bicyclic, or tricyclic hydrocarbon ring systems, including bridged, spiro, and/or fused ring systems, in which at least one of the rings is aromatic. An aryl group may contain 6 (i.e., phenyl) or about 9 to about 15 ring atoms, such as about 6 to about 8 ring atoms or about 9 to about 11 ring atoms. In some embodiments, aryl groups include, but are not limited to, naphthyl, indanyl, indenyl, anthryl, phenanthryl, fluorenyl, 1,2,3,4-tetrahydronaphthalenyl, 6,7,8,9-tetrahydro-5H-benzocycloheptenyl, and 6,7,8,9-tetrahydro-5H-benzocycloheptenyl. The aryl may be unsubstituted or substituted as described herein. The substitution may be on any carbon-atom, as permitted by the stability and valency of the substituent. 
     The term “aryloxy” as used herein refers to the O-(aryl) group, where the point of attachment is through the oxygen-atom and the aryl group is defined above. In some examples, the alkyl is a phenoxy or napthoxy. 
     “Heteroaryl” refers to a 5- to 18-membered unsaturated or partially unsaturated radical (e.g., C5-13heteroaryl) that includes one or more ring heteroatoms selected from nitrogen, oxygen and sulfur. In some embodiments, the heteroaryl is monocyclic, bicyclic, tricyclic or tetracyclic. In other embodiments, the heteroatom(s) in the heteroaryl are optionally oxidized. The heteroaryl may be attached to the rest of the molecule through any atom of the ring(s). In some embodiments, the heteroaryl has 3 to about 18 ring atoms. In some embodiments, heteroaryl groups include 4 to about 8 ring atoms. In other embodiments, heteroaryl groups include 5 to about 7 ring atoms. Examples of heteroaryls include, but are not limited to, azepinyl, acridinyl, benzimidazolyl, benzindolyl, 1,3-benzodioxolyl, benzofuranyl, benzooxazolyl, benzo[d]thiazolyl, benzothiadiazolyl, benzo[b][1,4]dioxepinyl, benzo[b][1,4]oxazinyl, 1,4-benzodioxanyl, benzonaphthofuranyl, benzoxazolyl, benzodioxolyl, benzodioxinyl, benzoxazolyl, benzopyranyl, benzopyranonyl, benzofuranyl, benzofuranonyl, benzofurazanyl, benzothiazolyl, benzothienyl (benzothiophenyl), benzothieno[3,2-d]pyrimidinyl, benzotriazolyl, benzo[4,6]imidazo[1,2-a]pyridinyl, carbazolyl, cinnolinyl, cyclopenta[d]pyrimidinyl, 6,7-dihydro-5H-cyclopenta[4,5]thieno[2,3-d]pyrimidinyl, 5,6-dihydrobenzo[h]quinazolinyl, 5,6-dihydrobenzo[h]cinnolinyl, 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-c]pyridazinyl, dibenzofuranyl, dibenzothiophenyl, furanyl, furazanyl, furanonyl, furo[3,2-c]pyridinyl, 5,6,7,8,9,10-hexahydrocycloocta[d]pyrimidinyl, 5,6,7,8,9,10-hexahydrocycloocta[d]pyridazinyl, 5,6,7,8,9,10-hexahydrocycloocta[d]pyridinyl, isothiazolyl, imidazolyl, indazolyl, indolyl, indazolyl, isoindolyl, indolinyl, isoindolinyl, isoquinolyl, indolizinyl, isoxazolyl, 5,8-methano-5,6,7,8-tetrahydroquinazolinyl, naphthyridinyl, 1,6-naphthyridinonyl, oxadiazolyl, 2-oxoazepinyl, oxazolyl, oxiranyl, 5,6,6a,7,8,9,10,10a-octahydrobenzo[h]quinazolinyl, 1-phenyl-1H-pyrrolyl, phenazinyl, phenothiazinyl, phenoxazinyl, phthalazinyl, pteridinyl, purinyl, pyranyl, pyrrolyl, pyrazolyl, pyrazolo[3,4-d]pyrimidinyl, pyridinyl, pyrido[3,2-d]pyrimidinyl, pyrido[3,4-d]pyrimidinyl, pyrazinyl, pyrimidinyl, pyridazinyl, pyrrolyl, quinazolinyl, quinoxalinyl, quinolinyl, isoquinolinyl, tetrahydroquinolinyl, 5,6,7,8-tetrahydroquinazolinyl, 5,6,7,8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidinyl, 6,7,8,9-tetrahydro-5H-cyclohepta[4,5]thieno[2,3-d]pyrimidinyl, 5,6,7,8-tetrahydropyrido[4,5-c]pyridazinyl, thiazolyl, thiadiazolyl, thiapyranyl, triazolyl, tetrazolyl, triazinyl, thieno[2,3-d]pyrimidinyl, thieno[3,2-d]pyrimidinyl, thieno[2,3-c]pyridinyl, and thiophenyl (i.e. thienyl). In some embodiments, the heteroaryl is pyridyl. In other embodiments, the heteroaryl is imidazole. The heteroaryl may be unsubstituted or substituted as described herein. The substitution may be on a carbon-atom or heteroatom, as permitted by the stability and valency of the substituent. For example, one N-atom of an imidazole may be substituted. Further, any available carbon-atom may be doubly bonded to an oxygen, i.e., the carbon-atom contains an oxo (═O) group or formyl group (CH═O). 
     “Substituted” means that the referenced group may have one or more additional groups, radicals or moieties attached. Such groups include, independently, alkyl, cycloalkyl, aryl, heteroaryl, heterocyclyl, alkoxy, aryloxy, OH, CN, halide, NO 2 , SO 3 R (where R is H, halide, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl) such as SO 3 H or SO 3 C1, C(O)OR (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl), OC(O)OR (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl) such as OCO 2 alkyl, OC(O)R (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl) such as OC(O)alkyl, PO 3 R 2  (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl), NR 2  (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl), or a quaternary amine such as R═(CH2) z N + (R 1 ) 3 X − , wherein z is 1 or greater (such as z is I to 10, 1 to 5, 2 to 10, 2 to 8, or 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10), R 10  is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl, and X is a counteranion as described herein. Examples of R═(CH 2 ) z N + (R 10 ) 3 X −  include, without limitation, R 10 —N(CH 3 ) 3 , R 10 —N(CH 2 CH 3 ) 3 , R 10 —NH(CH 3 ) 2 , R 10 —NH(CH 2 CH 3 ) 2 , R 10 —NH 2 CH 3 , R 10 —NH 2 (CH 2 CH 3 ), or R 10 —NH 3 . The substituents themselves may be substituted, for example, a cycloalkyl substituent may itself have a halide substituent at one or more of its ring carbons. In some embodiments, the substituents noted above may be further substituted with NR 3  (where R is H, OH, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl) such as N(CH 3 ) 3  or the like. For example, the substituent may be betainyl (OC(O)CH 2 N(CH 3 ) 3 ), cholinyl (OCH 2 CH 2 N(CH 3 ) 3 ), or carnitinyl (OC(O)CH 2 CH(OH)CH 2 N(CH 3 ) 3 ). The term “optionally substituted” means optional substitution with the specified groups, radicals or moieties. 
     As used herein, the term “counteranion” as used herein refers to an anion which balances the charge of the base molecule. In some embodiments, any anion which provides a stable salt may be selected. In other embodiments, the anion is acetate, propionate, lactate, citrate, tartrate, succinate, fumarate, maleate, malonate, mandelate, phthalate, Cl, Br, I, F, phosphate, nitrate, sulfate, methanesulfonate, ethanesulfonate, phosphonate, napthalenesulfonate, benzenesulfonate, toluenesulfonate, camphorsulfonate, methanesulfate, ethanesulfate, napthalenesulfate, benzenesulfate, toluenesulfate, camphorsulfate, bisulfate, sulfite, or bisulfite. 
     In other aspects, the indigo compounds have an affinity to a substrate, as defined herein. The term “affinity to a substrate” as used herein refers to the ability of the dye compound to dye a substrate as described herein as well as leuco-indigo. In some embodiments, the affinity of the indigo compounds to a textile is equal to or within a factor of about 2 to about 3 compared with leuco-indigo. In some embodiments, the affinity is to a textile such as cotton. Such measurements may be made by quantifying the indigo content using post-treatment methods such as sodium hydrosulfite, followed by UV-Vis spectrophotometry as described in Hauser, Improved Determination of Indigo, Textile Chemist and Coloris &amp; American Dyestuff Reporter, 32(2):33, December 2000, which is incorporated herein by reference. 
     In further aspects, the indigo compounds convert to indigo upon removing the modification. 
     In yet other aspects, the indigo compound is not: 
     (i) N,N′-dinicotinoyl-[2,2′-biindolinylidene]-3,3′-dione; 
     (i) the N″,N″′-methylpyridinium bis(methylsulfate) salt of N,N′-dinicotinoyl-[2,2′-biindolinylidene]-3,3′-dione; 
     (iii) N,N′-diacetyl-[2,2′-biindolinylidene]-3,3′-dione; 
     (iv) N,N′-dipropionyl-[2,2′-bi-indolinylidene]-3,3′-dione; 
     (v) N,N′-di-isobutyryl-[2,2′-biindolinylidene]-3,3′-dione; 
     (vi) N,N′-dipivaloyl-[2,2′-biindolinylidene]-3,3′-dione; 
     (vii) N,N′-bis(cyclohexylcarbonyl)-2,2′-bi-indolinylidene-3,3′-dione; 
     (viii) N,N′-bis(3-phenylpropionyl)-2,2′-bi-indolinylidene-3,3′-dione; 
     (ix) N,N′-bis(ethoxycarbonylacetyl)-2,2′-bi-indolinylidene-3,3′-dione; 
     (x) N,N′-bis(2-phenylacetyl)-[2,2′-bi-indolinylidene]-3,3′-dione; 
     (xi) N,N′-bis-(p-methoxyphenylacetyl)2,2′-bi-indolinylidene-3,3′-dione; 
     (xii) N,N′-bis(1-naphthylacetyl)-2,2′-bi-indolinylidene-3,3′-dione; 
     (xiii) N,N′-bis(2-phenylbutyryl)-2,2′-indolinylidene-3,3′-dione; or 
     (xiv) (E)-1,1′-di(adamantane-1-carbonyl)-[2,2′-biindolinylidene]-3,3′-dione. 
     Thus, in some embodiments, the compound is of Formula (I) or a salt thereof. 
     
       
         
         
             
             
         
       
     
     R 1  and R 2  may be the same or differ. In some embodiments, one of R 1  and R 2  is H. In further embodiments, one of R 1  and R 2  is SO 3 H. 
     R 1  and R 2  may be, independently, H, S3R C , SO 2 R C , PO 3 (R C ) 2 , C(O)-(optionally substituted C 1-9 glycolyl), C(O)-(optionally substituted C 1-6 alkyl), C(O)-(optionally substituted C 1-6 hydroxyalkyl), C(O)O-(optionally substituted C 1-9 glycolyl), C(O)-(optionally substituted heteroaryl), C(O)-(optionally substituted aryl), C(O)-(optionally substituted heterocyclyl), C(O)NR A R B , C(O)O-(optionally substituted C 1-6 alkyl), C(O)O-(optionally substituted C 1-6 hydroxyalkyl), C(O)O-(optionally substituted heteroaryl), C(O)O-(optionally substituted aryl), or C(O)O-(optionally substituted heterocyclyl). In some embodiments, R 1  and R 2  are, independently, H, SO 3 R C , SO 2 R C , PO 3 (R C ) 2 , C(O)-(optionally substituted C 1-9 glycolyl), C(O)-(optionally substituted C 1-6 hydroxyalkyl), C(O)-(optionally substituted C 1-9 glycolyl), C(O)-(optionally substituted aryl), C(O)-(optionally substituted heterocyclyl), C(O)NR A R B , C(O)O-(optionally substituted C 1-6 alkyl), C(O)O-(optionally substituted C 1-6 hydroxyalkyl), C(O)O-(optionally substituted heteroaryl), C(O)O-(optionally substituted aryl), or C(O)O-(optionally substituted heterocyclyl). 
     In some embodiments, R 1  is C(O)-(optionally substituted alkyl) such as C(O)(C 1-6 alkyl substituted with an ester such as C(O)—(C 1-6 alkoxy) or C(O)(C 1-6 alkyl substituted with aryl such. In other embodiments, R 1  is C(O)-(optionally substituted alkyl) such as C(O)(C 1-6 alkyl substituted with an ester such as C(O)methoxy, C(O)propoxy, C(O)butoxy, C(O)pentoxy, or C(O)hexoxy) or C(O)(C 1-6 alkyl substituted with an aryl such as phenyl substituted with alkyl, cycloalkyl, aryl, heteroaryl, heterocyclyl, alkoxy, aryloxy, OH, CN, or halide, substituted naphthyl, indanyl, indenyl, anthryl, phenanthryl, fluorenyl, 1,2,3,4-tetrahydronaphthalenyl, 6,7,8,9-tetrahydro-5H-benzocycloheptenyl, or 6,7,8,9-tetrahydro-5H-benzocycloheptenyl; C(O)—(C 3-6 alkyl such as n-propyl, n-butyl, i-butyl, pentyl, or hexyl). In further embodiments, R 1  is C(O)NR A R B , where R A  and R B  are, independently, H, optionally substituted C 1-6 alkyl, optionally substituted C 1-6 hydroxyalkyl, or optionally substituted aryl. In still other embodiments, R 1  is C(O)-(optionally substituted heteroaryl). In yet further embodiments, R 1  is C(O)O-(optionally substituted heteroaryl). In other embodiments, R 1  is C(O)-(optionally substituted aryl). In further embodiments, R 1  is C(O)O-(optionally substituted aryl). In yet other embodiments, R 1  is C(O)-(optionally substituted heterocyclyl). In other embodiments, R 1  is SO 3 H. Preferably, R 1  is C(O)-(optionally substituted pyridyl), such as C(O)-(optionally substituted 2-pyridyl), C(O)-(optionally substituted 3-pyridyl), or C(O)-(optionally substituted 4-pyridyl). In further embodiments, the pyridyl is substituted with one or more C 1-6 alkyl, such as methyl or ethyl. Preferably, the pyridyl is substituted on the N-atom of the pyridyl ring. In other embodiments, R 1  is C(O)-(optionally substituted aryl) such as C(O)-(optionally substituted phenyl). Preferably, the phenyl of the R 1  group is substituted with one or more SO 3 H, SO 3 C 1 , NO 2 , NH 2 , OH, halide, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl. In yet further embodiments, R 1  is C(O)NR A R B , wherein one or both of R A  and R B  is H, optionally substituted C 1-6 hydroxyalkyl such as methylhydroxy, ethylhydroxy, propylhydroxy, butylhydroxy, pentylhydroxy, or hexylhydroxy, or optionally substituted C 1-6 alkyl such as CH 2 C(O)OH, CH 2 CH 2 C(O)OH, CH 2 CH 2 CH 2 C(O)OH. In still other embodiments, R 1  is C(O)O-(optionally substituted heterocyclyl) such as C(O)O-(optionally substituted succinic anhydride). In further embodiments, R 1  is C(O)O-(optionally substituted alkyl) such as C(O)O(alkyl substituted with heterocyclyl) such as C(O)O(alkyl substituted with a monosaccharide such as glucosyl). In other embodiments, R 1  is C(O)(optionally substituted C 1-6 hydroxyalkyl) such as C(O)CH 2 OH, C(O)CH 2 CH 2 OH, C(O)CHOHCH 2 OH, C(O)CH 2 CHOHCH 3 , or C(O)CH 2 CHOHCH 2 OH. In yet other embodiments, R 1  is C(O)O(optionally substituted C 1-6 hydroxyalkyl) such as C(O)OCH 2 OH, C(O)OCH 2 CH 2 OH, C(O)OCHOHCH 2 OH, C(O)OCH 2 CHOHCH 3 , or C(O)OCH 2 CHOHCH 2 OH. In further embodiments, R 1  is C(O)O(optionally substituted C 1-9 glycol) such as C(O)OCH 2 CH 2 OCH 3 , C(O)(OCH 2 CH 2 ) 2 OCH 3 , or C(O)(OCH 2 CH 2 ) 3 OCH 3 . In still further embodiments, R 1  is SO 3 R C , where R C  is H, OH, optionally substituted C 1-6 alkyl, optionally substituted C 3-6 cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl such as H, OH, optionally substituted C 1-6 alkyl, or optionally substituted aryl. For example, R C  in SO 3 R C  is OH. In other embodiments, R 1  is SO 2 R C , where R C  is H, optionally substituted C 1-6 alkyl, optionally substituted C 3-6 cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl such as H, optionally substituted C 1-6 alkyl, or optionally substituted aryl. For example, R C  in SO 2 R C  is aryl substituted with C(O)OH. 
     In some embodiments, R 2  is C(O)-(optionally substituted alkyl) such as C(O)(C 1-6 alkyl substituted with an ester such as C(O)C 1-6 alkoxy). In other embodiments, R 2  is C(O)-(optionally substituted alkyl) such as C(O)(C 1-6 alkyl substituted with an ester such as C(O)methoxy, C(O)propoxy, C(O)butoxy, C(O)pentoxy, or C(O)hexoxy) or C(O)(C 1-6 alkyl substituted with an aryl such as (phenyl substituted with alkyl, cycloalkyl, aryl, heteroaryl, heterocyclyl, alkoxy, aryloxy, OH, CN, or halide), substituted naphthyl, indanyl, indenyl, anthryl, phenanthryl, fluorenyl, 1,2,3,4-tetrahydronaphthalenyl, 6,7,8,9-tetrahydro-5H-benzocycloheptenyl, or 6,7,8,9-tetrahydro-5H-benzocycloheptenyl; C(O)—(C 3-6 alkyl such as n-propyl, n-butyl, i-butyl, pentyl, or hexyl). In other embodiments, R 2  is C(O)O-(optionally substituted alkyl). In further embodiments, R 2  is C(O)NR A R B , where R A  and R B  are, independently, H or optionally substituted C 1-6 alkyl, or optionally substituted aryl. In still other embodiments, R 2  is C(O)-(optionally substituted heteroaryl). In yet further embodiments, R 2  is C(O)O-(optionally substituted heteroaryl). In other embodiments, R 2  is C(O)-(optionally substituted aryl). In further embodiments, R 2  is C(O)O-(optionally substituted aryl). In yet other embodiments, R 2  is C(O)-(optionally substituted heterocyclyl). In still further embodiments, R 2  is C(O)O-(optionally substituted heterocyclyl). In other embodiments, R 2  is SO 3 H. Preferably, R 2  is C(O)-(optionally substituted pyridyl), such as C(O)-(optionally substituted 2-pyridyl), C(O)-(optionally substituted 3-pyridyl), or C(O)-(optionally substituted 4-pyridyl). In further embodiments, the pyridyl is substituted with one or more C 1-6 alkyl, such as methyl or ethyl. Preferably, the pyridyl is substituted on the N-atom of the pyridyl ring. In other embodiments, R 2  is C(O)-(optionally substituted aryl) such as C(O)-(optionally substituted phenyl). Preferably, the phenyl of the R 2  group is substituted with one or more SO 3 H, SO 3 C 1 , NO 2 , NH 2 , OH, halide, alkyl, aryl, cycloalkyl, heteroaryl, heterocyclyl and as substituents. In yet further embodiments, R 2  is C(O)NR A R B , wherein one or both of R A  and R B  is H, optionally substituted C 1-6 hydroxyalkyl such as methylhydroxy, ethylhydroxy, propylhydroxy, butylhydroxy, pentylhydroxy, or hexylhydroxy, or optionally substituted C 1-6 alkyl such as CH 2 C(O)OH, CH 2 CH 2 C(O)OH, CH 2 CH 2 CH 2 C(O)OH. In still other embodiments, R 2  is C(O)O-(optionally substituted heterocyclyl) such as C(O)O-(optionally substituted succinic anhydride). 
     In further embodiments, R 2  is C(O)O-(optionally substituted alkyl) such as C(O)O(alkyl substituted with heterocyclyl) such as C(O)O(alkyl substituted with a monosaccharide such as glucosyl). In other embodiments, R 2  is C(O)(optionally substituted C 1-6 hydroxyalkyl) such as C(O)CH 2 OH, C(O)CH 2 CH 2 OH, C(O)CHOHCH 2 OH, C(O)CH 2 CHOHCH 3 , or C(O)CH 2 CHOHCH 2 OH. In yet other embodiments, R 2  is C(O)O(optionally substituted C 1-6 hydroxyalkyl) such as C(O)OCH 2 OH, C(O)OCH 2 CH 2 OH, C(O)OCHOHCH 2 OH, C(O)OCH 2 CHOHCH 3 , or C(O)OCH 2 CHOHCH 2 OH. In further embodiments, R 2  is C(O)O(optionally substituted C 1-9 glycol) such as C(O)OCH 2 CH 2 OCH 3 , C(O)(OCH 2 CH 2 ) 2 OCH 3 , or C(O)(OCH 2 CH 2 ) 3 OCH 3 . In still further embodiments, R 2  is SO 3 R C , where R C  is H, optionally substituted C 1-6 alkyl, optionally substituted C 3-6 cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl such as H, optionally substituted C 1-6 alkyl, or optionally substituted aryl. For example, R C  in SO 3 R C  is aryl substituted with C(O)OH. 
     In other embodiments, R 2  is SO 2 R C , where R C  is H, optionally substituted C 1-6 alkyl, optionally substituted C 3-8 cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl such as H, optionally substituted C 1-6 alkyl, or optionally substituted aryl. For example, R C  in SO 2 R C  is aryl substituted with C(O)OH. 
     In certain embodiments, R 3  and R 4  are selected such that they do not affect the properties afforded by the R 1  and/or R 2  groups, i.e., solubility and hydrolysis to name a few. In some embodiments, R 3  and R 4  are, independently, H, halide, optionally substituted C 1-6 alkyl, optionally substituted C 1-6 alkoxy, SO 3 H, or optionally substituted aryl. In some embodiments, R 3  is halide such as Cl, Br, F, or I. In some embodiments, R 4  is halide such as Cl, Br, F, or I. In other embodiments, R 3  is C 1-6 alkyl such as methyl, ethyl, propyl, butyl, pentyl, or hexyl. In further embodiments, R 3  is C 1-6 alkoxy, such as methoxy, ethoxy, propoxy, butoxy, pentoxy, or hexoxy. 
     In still other embodiments, R 3  is SO 3 H. In yet further embodiments, R 4  is C 1-6 alkyl such as methyl, ethyl, propyl, butyl, pentyl, or hexyl. In other embodiments, R 4  is C 1-6 alkoxy, such as methoxy, ethoxy, propoxy, butoxy, pentoxy, or hexoxy. In further embodiments, R 4  is SO 3 H. 
     In the structure of Formula (I), m and n are, independently, 0 to 4. In some embodiments, m and n are the same. In other embodiments, m and n differ. In further embodiments, m is 0. In yet other embodiments, n is 0. In still other embodiments, m and n are 1. In yet further embodiments, m and n are 2. In other embodiments, m and n are 3. In further embodiments, m and n are 4. 
     In some aspects, R 3  and R 4  are not H, when R 1  and R 2  are both 1-methyl-pyrid-3-yl or pyrid-3-yl. However, the compound where R 3  and R 4  are H, when R 1  and R 2  are both 1-methyl-pyrid-3-yl or pyrid-3-yl, i.e., the following compounds, may be used in the methods described herein. 
     (i) N,N′-dinicotinoyl-[2,2′-biindolinylidene]-3,3′-dione; 
     (i) the N″,N″′-methylpyridinium bis(methylsulfate) salt of N,N′-dinicotinoyl-[2,2′-biindolinylidene]-3,3′-dione; 
     (iii) N,N′-diacetyl-[2,2′-biindolinylidene]-3,3′-dione; 
     (iv) N,N′-dipropionyl-[2,2′-bi-indolinylidene]-3,3′-dione; 
     (v) N,N′-di-isobutyryl-[2,2′-biindolinylidene]-3,3′-dione; 
     (vi) N,N′-dipivaloyl-[2,2′-biindolinylidene]-3,3′-dione; 
     (vii) N,N′-bis(cyclohexylcarbonyl)-2,2′-bi-indolinylidene-3,3′-dione; 
     (viii) N,N′-bis(3-phenylpropionyl)-2,2′-bi-indolinylidene-3,3′-dione; 
     (ix) N,N′-bis(ethoxycarbonylacetyl)-2,2′-bi-indolinylidene-3,3′-dione; 
     (x) N,N′-bis(2-phenylacetyl)-[2,2′-bi-indolinylidene]-3,3′-dione; 
     (xi) N,N′-bis-(p-methoxyphenylacetyl)2,2′-bi-indolinylidene-3,3′-dione; 
     (xii) N,N′-bis(I-naphthylacetyl)-2,2′-bi-indolinylidene-3,3′-dione; 
     (xiii) N,N′-bis(2-phenylbutyryl)-2,2′-indolinylidene-3,3′-dione; or 
     (xiv) (E)-1,1′-di(adamantane-1-carbonyl)-[2,2′-biindolinylidene]-3,3′-dione. 
     In some preferred embodiments, the compound of Formula (I) is Formulae (I-A)-(I-I): 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In these structures, R 5  and R 6  are, independently, H or C 1-6 alkyl and X is halide, sulfate, C 1-6 alkyl sulfate, bisulfate, or phosphate. In some embodiments, R 5  and R 6  are H. In other embodiments, R 5  and R 6  are C 1-6 alkyl. In further embodiments, X is halide. In still other embodiments, X is C 1-6 alkyl sulfate such as MeSO 4 . In yet further embodiments, X is bisulfate. 
     In other embodiments, X is phosphate. For the compound of Formula (I-C), both R 5  and R 6  are not CH 3  when X is CH 3 SO 4 —. 
     In some embodiments, preferred compounds encompassed by Formula (I) include the following. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In other preferred embodiments, the compound of Formula (I) is the following: 
     
       
         
         
             
             
         
       
     
     wherein X is not CH 3 SO 4 . 
     In some preferred embodiments, the compound of Formula (I) is Formulae (I-J)-(I-R): 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In these structures, R 3  and R 4  are, independently, halide, preferably Br, R 5  and R 6  are, independently, H or C 1-6 alkyl and X is halide, sulfate, C 1-6 alkyl sulfate, bisulfate, or phosphate. In some embodiments, R 5  and R 6  are H. In other embodiments, R 5  and R 6  are C 1-6 alkyl. In further embodiments, X is halide. In still other embodiments, X is C 1-6 alkyl sulfate. In yet further embodiments, X is bisulfate. In other embodiments, X is phosphate. 
     In other embodiments, preferred compounds encompassed by Formula (I) are the following. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In the above compounds, X is a counteranion as described herein. In further embodiments, preferred compounds encompassed by Formula (I) include the following or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In further embodiments, preferred compounds encompassed by Formula (I) are the following. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In still further embodiments, preferred compounds encompassed by Formula (I) is of Formula (I-S) or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In this structure of Formula (I-S), R 9  and R 10  are, independently alkyl, cycloalkyl, aryl, heteroaryl, heterocyclyl, alkoxy, aryloxy, OH, CN, halide, NO 2 , SO 3 R (where R is H, halide, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl) such as SO 3 H or SO 3 C 1 , C(O)OR (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl), OC(O)OR (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl) such as OCO 2 alkyl, OC(O)R (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl) such as OC(O)alkyl, PO 3 R 2  (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl), NR 2  (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl), or a quaternary amine, x is 0-5, and y is 0-5. In some embodiments, R 9  and R 10  are SO 3 H or SO 3 C 1 . In other embodiments, R 9  and R 10  are NO 2 , NH 2 , OH, halide, C 1-6 alkyl, aryl, C 3-8 cycloalkyl, heteroaryl, or heterocyclyl. In further embodiments, x is 1. In yet other embodiments, y is 1. In still further embodiments, x and y are 1. In yet other embodiments, preferred compounds encompassed by Formula (I) are the following or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In further embodiments, preferred compounds encompassed by Formula (I) is of Formula (I-T) or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In this structure of Formula (I-T), each R C  is, independently, H, optionally substituted C 1 -6alkyl, optionally substituted C 3-8 cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl. In some aspects, each R C  is H, optionally substituted C 1-6 alkyl, or optionally substituted aryl. In some aspects, R C  is optionally substituted aryl such as optionally substituted phenyl. In further aspects, R C  is aryl substituted with C(O)OH. 
     In further embodiments, preferred compounds encompassed by Formula (I) is of Formula (I-TI) or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In this structure of Formula (I-T1), R 9  and R 10  are, independently alkyl, cycloalkyl, aryl, heteroaryl, heterocyclyl, alkoxy, aryloxy, OH, CN, halide, NO 2 , SO 3 R (where R is H, halide, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl) such as SO 3 H or SO 3 C 1 , C(O)R (where R is H, NH 2 , alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl), C(O)OR (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl), OC(O)OR (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl) such as OCO 2 alkyl, OC(O)R (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl) such as OC(O)alkyl, PO 3 R 2  (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl), NR 2  (where R is H, alkyl, aryl, cycloalkyl, heteroaryl, or heterocyclyl), or a quaternary amine, x is 0-5, and y is 0-5. In some embodiments, R 9  and R 10  are C(O)OR such as CO 2 H, C(O)NH 2 , or NO 2 . In other embodiments, R 9  and R 10  are C 1-6 alkyl. In further embodiments, x is 1. In yet other embodiments, y is 1. In still further embodiments, x and y are 1. 
     In some embodiments, a preferred compound encompassed by Formula (I) is the following or a salt thereof: 
     
       
         
         
             
             
         
       
     
     In further embodiments, preferred compounds encompassed by Formula (I) is of Formula (I-V) or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In this structure of Formula (I-U), each R C  is, independently, H, optionally substituted C 1-6 alkyl, optionally substituted C 3-6 cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl such as H, optionally substituted C 1-6 alkyl, or optionally substituted aryl. In other aspects, R C  is H. 
     In some embodiments, a preferred compound encompassed by Formula (I) is the following or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In further embodiments, preferred compounds encompassed by Formula (I) is of Formula (I-W) or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In this structure of Formula (I-W), one or both of R A  and R B  is H, optionally substituted C 1-6 hydroxyalkyl, optionally substituted C 1-6 alkyl, or optionally substituted aryl. In some embodiments, one or both of R A  and R B  is methylhydroxy, ethylhydroxy, propylhydroxy, butylhydroxy, pentylhydroxy, or hexylhydroxy. In other embodiments, one or both of R A  and R B  is CH 2 C(O)OH, CH 2 CH 2 C(O)OH, or CH 2 CH 2 CH 2 C(O)OH. 
     In further embodiments, preferred compounds encompassed by Formula (I) are the following or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In further embodiments, preferred compounds encompassed by Formula (I) is of Formula (I-X) or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In this structure of Formula (I-X), one or both R E  is H, optionally substituted C 1-6 alkyl, C 1-6 hydroxyalkyl, optionally substituted aryl, optionally substituted C 3-8 cycloalkyl, optionally substituted heteroaryl, or optionally substituted heterocyclyl. In some aspects, R E  is optionally substituted C 1-6 alkyl such as C(O)O(alkyl substituted with heterocyclyl), e.g., C(O)O(alkyl substituted with a monosaccharide such as glucosyl). In other aspects, R E  is optionally substituted C 1-6 hydroxyalkyl such as C(O)OCH 2 OH, C(O)OCH 2 CH 2 OH, C(O)OCHOHCH 2 OH, C(O)OCH 2 CHOHCH 3 , or C(O)OCH 2 CHOHCH 2 OH. In further aspects, R E  is optionally substituted heterocyclyl such as optionally substituted succinic anhydride. In yet other aspects, R E  is optionally substituted C 1-9 glycol such as C(O)OCH 2 CH 2 OCH 3 , C(O)(OCH 2 CH 2 ) 2 OCH 3 , or C(O)(OCH 2 CH 2 ) 3 OCH 3 . 
     In other embodiments, preferred compounds encompassed by Formula (I) are the following or a salt thereof. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In further embodiments, preferred compounds encompassed by Formula (I) is of Formula (I-Y) or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In this structure of Formula (I-X), one or both R E  is H, optionally substituted C 1-6 alkyl (such as substituted methyl, n-propyl, substituted i-propyl, alkyl substituted with phenyl substituted with alkyl, cycloalkyl, aryl, heteroaryl, heterocyclyl, alkoxy, aryloxy, OH, CN, or halide), alkyl substituted with naphthyl, alkyl substituted with indanyl, alkyl substituted with indenyl, alkyl substituted with anthryl, alkyl substituted with phenanthryl, alkyl substituted with fluorenyl, alkyl substituted with 1,2,3,4-tetrahydronaphthalenyl, alkyl substituted with 6,7,8,9-tetrahydro-5H-benzocycloheptenyl, or alkyl substituted with 6,7,8,9-tetrahydro-5H-benzocycloheptenyl), optionally substituted C 1-6 hydroxyalkyl, optionally substituted heterocyclyl, or optionally substituted C 1-6 hydroxyalkyl. In some aspects, R E  is optionally substituted C 1-6 hydroxyalkyl such as C(O)CH 2 OH, C(O)CH 2 CH 2 OH, C(O)CHOHCH 2 OH, C(O)CH 2 CHOHCH 3 , or C(O)CH 2 CHOHCH 2 OH. In other aspects, R E  is optionally substituted C 1-6 alkyl such as C 1-6 alkyl substituted with an ester, e.g., C(O)methoxy, C(O)propoxy), C(O)butoxy, C(O)pentoxy, or C(O)hexoxy. 
     In other embodiments, preferred compounds encompassed by Formula (I) is the following or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In further embodiments, the compound is of Formula (II) or a salt thereof: 
     
       
         
         
             
             
         
       
     
     In the structure of Formula (II), all of R 1 , R 2 , R 7 , and R 8  are not H. R 1  and R 2  may be the same or different. In some embodiments, R 1  or R 2  is H. In other embodiments, R 1  and R 2  are H. 
     R 1  and R 2  are, independently, H, SO 3 R C , SO 2 R C , PO 3 (R C ) 2 , C(O)-(optionally substituted C 1-9 glycolyl), C(O)-(optionally substituted C 1-6 alkyl), C(O)-(optionally substituted C 1-6 hydroxyalkyl), C(O)-(optionally substituted C 1-9 glycolyl), C(O)-(optionally substituted heteroaryl), C(O)-(optionally substituted aryl), C(O)-(optionally substituted heterocyclyl), C(O)NR A R B , C(O)O-(optionally substituted C 1-6 alkyl), C(O)O-(optionally substituted C 1-6 hydroxyalkyl), C(O)O-(optionally substituted heteroaryl), C(O)O-(optionally substituted aryl), or C(O)O-(optionally substituted heterocyclyl); 
     In some embodiments, R 1  is C(O)-(optionally substituted alkyl) such as C(O)(C 1-6 alkyl substituted with an ester such as C(O)C 1-6 alkoxy). In other embodiments, R 1  is C(O)O-(optionally substituted alkyl). In further embodiments, R 1  is C(O)NR A R B , where R A  and R B  are, independently, H or optionally substituted C 1-6 alkyl, or optionally substituted aryl. In still other embodiments, R 1  is C(O)-(optionally substituted heteroaryl). In yet further embodiments, R 1  is C(O)O-(optionally substituted heteroaryl). In other embodiments, R 1  is C(O)-(optionally substituted aryl). In further embodiments, R 1  is C(O)O-(optionally substituted aryl). In yet other embodiments, R 1  is C(O)-(optionally substituted heterocyclyl). In still further embodiments, R 1  is C(O)O-(optionally substituted heterocyclyl). In other embodiments, R 1  is SO 3 H. Preferably, R 1  is C(O)-(optionally substituted pyridyl), such as C(O)-(optionally substituted 2-pyridyl), C(O)-(optionally substituted 3-pyridyl), or C(O)-(optionally substituted 4-pyridyl). In further embodiments, the pyridyl is substituted with one or more C 1-6 alkyl, such as methyl or ethyl. Preferably, the pyridyl is substituted on the N-atom of the pyridyl ring. In other embodiments, R 1  is C(O)-(optionally substituted aryl) such as C(O)-(optionally substituted phenyl). Preferably, the phenyl of the R 1  group is substituted with one or more SO 3 H, SO 3 C 1 , NO 2 , NH 2 , OH, halide, alkyl, aryl, cycloalkyl, heteroaryl, heterocyclyl and as substituents. In yet further embodiments, R 1  is C(O)NR A R B , wherein one or both of R A  and R B  is H, optionally substituted C 1-6 hydroxyalkyl such as methylhydroxy, ethylhydroxy, propylhydroxy, butylhydroxy, pentylhydroxy, or hexylhydroxy, or optionally substituted C 1-6 alkyl such as CH 2 C(O)OH, CH 2 CH 2 C(O)OH, CH 2 CH 2 CH 2 C(O)OH. In still other embodiments, R 1  is C(O)O-(optionally substituted heterocyclyl) such as C(O)O-(optionally substituted succinic anhydride). In further embodiments, R 1  is C(O)O-(optionally substituted alkyl) such as C(O)O(alkyl substituted with heterocyclyl) such as C(O)O(alkyl substituted with a monosaccharide such as glucosyl). In other embodiments, R 1  is C(O)(optionally substituted C 1-6 hydroxyalkyl) such as C(O)CH 2 OH, C(O)CH 2 CH 2 OH, C(O)CHOHCH 2 OH, C(O)CH 2 CHOHCH 3 , or C(O)CH 2 CHOHCH 2 OH. In yet other embodiments, R 1  is C(O)O(optionally substituted C 1-6 hydroxyalkyl) such as C(O)OCH 2 H, C(O)OCH 2 CH 2 OH, C(O)OCHOHCH 2 OH, C(O)OCH 2 CHOHCH 3 , or C(O)OCH 2 CHOHCH 2 OH. In further embodiments, R 1  is C(O)(optionally substituted C 1-9 glycol) such as C(O)OCH 2 CH 2 OCH 3 , C(O)(OCH 2 CH 2 ) 2 OCH 3 , or C(O)(OCH 2 CH 2 ) 30 CH 3 . In still further embodiments, R 1  is SO 3 R C , where R C  is H, optionally substituted C 1-6 alkyl, optionally substituted C 3-6 cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl such as H, optionally substituted C 1-6 alkyl, or optionally substituted aryl. For example, R C  in SO 3 R C  is aryl substituted with C(O)OH. In other embodiments, R 1  is SO 2 R C , where R C  is H, optionally substituted C 1-6 alkyl, optionally substituted C 3-6 cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl such as H, optionally substituted C 1-6 alkyl, or optionally substituted aryl. For example, R C  in SO 2 R C  is aryl substituted with C(O)OH. 
     In some embodiments, R 2  is C(O)-(optionally substituted alkyl) such as C(O)(C 1-6 alkyl substituted with an ester such as C(O)C 1-6 alkox). In other embodiments, R 2  is C(O)O-(optionally substituted alkyl). In further embodiments, R 2  is C(O)NR A R B , where R A  and R B  are, independently, H or optionally substituted C 1-6 alkyl, or optionally substituted aryl. In still other embodiments, R 2  is C(O)-(optionally substituted heteroaryl). In yet further embodiments, R 2  is C(O)O-(optionally substituted heteroaryl). In other embodiments, R 2  is C(O)-(optionally substituted aryl). In further embodiments, R 2  is C(O)O-(optionally substituted aryl). In yet other embodiments, R 2  is C(O)-(optionally substituted heterocyclyl). In still further embodiments, R 2  is C(O)O-(optionally substituted heterocyclyl). In other embodiments, R 2  is SO 3 H. Preferably, R 2  is C(O)-(optionally substituted pyridyl), such as C(O)-(optionally substituted 2-pyridyl), C(O)-(optionally substituted 3-pyridyl), or C(O)-(optionally substituted 4-pyridyl). In further embodiments, the pyridyl is substituted with one or more C 1-6 alkyl, such as methyl or ethyl. Preferably, the pyridyl is substituted on the N-atom of the pyridyl ring. In other embodiments, R 2  is C(O)-(optionally substituted aryl) such as C(O)-(optionally substituted phenyl). Preferably, the phenyl of the R 2  group is substituted with one or more SO 3 H, SO 3 C 1 , NO 2 , NH 2 , OH, halide, alkyl, aryl, cycloalkyl, heteroaryl, heterocyclyl and as substituents. In yet further embodiments, R 2  is C(O)NR A R B , wherein one or both of R A  and R B  is H, optionally substituted C 1-6 hydroxyalkyl such as methylhydroxy, ethylhydroxy, propylhydroxy, butylhydroxy, pentylhydroxy, or hexylhydroxy, or optionally substituted C 1-6 alkyl such as CH 2 C(O)OH, CH 2 CH 2 C(O)OH, CH 2 CH 2 CH 2 C(O)OH. In still other embodiments, R 2  is C(O)O-(optionally substituted heterocyclyl) such as C(O)O-(optionally substituted succinic anhydride). In further embodiments, R 2  is C(O)O-(optionally substituted alkyl) such as C(O)O(alkyl substituted with heterocyclyl) such as C(O)O(alkyl substituted with a monosaccharide such as glucosyl). In other embodiments, R 2  is C(O)(optionally substituted C 1-6 hydroxyalkyl) such as C(O)CH 2 OH, C(O)CH 2 CH 2 OH, C(O)CHOHCH 2 OH, C(O)CH 2 CHOHCH 3 , or C(O)CH 2 CHOHCH 2 OH. In yet other embodiments, R 2  is C(O)O(optionally substituted C 1-6 hydroxyalkyl) such as C(O)OCH 2 H, C(O)OCH 2 CH 2 OH, C(O)OCHOHCH 2 OH, C(O)OCH 2 CHOHCH 3 , or C(O)OCH 2 CHOHCH 2 OH. In further embodiments, R 2  is C(O)(optionally substituted C 1-9 glycol) such as C(O)OCH 2 CH 2 OCH 3 , C(O)(OCH 2 CH 2 ) 2 OCH 3 , or C(O)(OCH 2 CH 2 ) 30 CH 3 . In still further embodiments, R 2  is SO 3 R C , where R C  is H, optionally substituted C 1-6 alkyl, optionally substituted C 3-6 cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl such as H, optionally substituted C 1-6 alkyl, or optionally substituted aryl. For example, R C  in SO 3 R C  is aryl substituted with C(O)OH. In other embodiments, R 2  is SO 2 R C , where R C  is H, optionally substituted C 1-6 alkyl, optionally substituted C 3-6 cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl such as H, optionally substituted C 1-6 alkyl, or optionally substituted aryl. For example, R C  in SO 2 R C  is aryl substituted with C(O)OH. 
     In some embodiments, R 3  and R 4  are, independently, H, halide, optionally substituted C 1-6 alkyl, optionally substituted C 1-6 alkoxy, SO 3 H, or optionally substituted aryl. In some embodiments, R 3  is halide such as Cl, Br, F, or I. In some embodiments, R 4  is halide such as C 1 , Br, F, or I. In other embodiments, R 3  is C 1-6 alkyl such as methyl, ethyl, propyl, butyl, pentyl, or hexyl. In further embodiments, R 3  is C 1-6 alkoxy, such as methoxy, ethoxy, propoxy, butoxy, pentoxy, or hexoxy. In still other embodiments, R 3  is SO 3 H. In yet further embodiments, R 4  is C 1-6 alkyl such as methyl, ethyl, propyl, butyl, pentyl, or hexyl. In other embodiments, R 4  is C 1-6 alkoxy, such as methoxy, ethoxy, propoxy, butoxy, pentoxy, or hexoxy. In further embodiments, R 4  is SO 3 H. 
     In some embodiments, R 7  and R 8  are, independently, H, SO 3 R C , SO 2 R C , PO 3 (R C ) 2 , C(O)NR A R B , C(O)-(optionally substituted C 1-6 alkyl), C(O)-(optionally substituted aryl), C(O)-(optionally substituted C 1-9 glycolyl), C(O)-(optionally substituted C 1-6 hydroxyalkyl), C(O)-(optionally substituted heteroaryl), C(O)-(optionally substituted heterocyclyl), C(O)O-(optionally substituted C 1-6 alkyl), C(O)O-(optionally substituted aryl), C(O)O-(optionally substituted C 1-9 glycolyl), C(O)O-(optionally substituted C 1-6 hydroxyalkyl), C(O)O-(optionally substituted heteroaryl), or C(O)O-(optionally substituted heterocyclyl). Preferably, both R 7  and R 8  are not SO 3 H. In other embodiments, R 7  and R 8  are, independently, H, SO 3 R C , SO 2 R C , PO 3 (R C ) 2 , C(O)NR A R B , C(O)-(optionally substituted C 1-9 glycolyl), C(O)-(optionally substituted heteroaryl), C(O)-(optionally substituted heterocyclyl), C(O)-(optionally substituted C 1-6 hydroxyalkyl), C(O)O-(optionally substituted aryl), C(O)O-(optionally substituted C 1-6 alkyl), C(O)O-(optionally substituted C 1-9 glycolyl), C(O)O-(optionally substituted C 1-6 hydroxyalkyl), C(O)O-(optionally substituted heteroaryl), or C(O)O-(optionally substituted heterocyclyl). 
     In some embodiments, R 7  and R 8  are, independently, H, SO 3 H, or C(O)C 1-6 alk-C(O)C 1-6 alkoxy. In further embodiments, R 7  or R 8  is H. In further embodiments, R 7  and R 8  are H. In other embodiments, R 7  or R 8  is SO 3 H. In yet further embodiments, R 7  and R 8  are SO 3 H. In still other embodiment, R7 and R8 are not both when both R 1  and R 2  are H. In further embodiments, R 7  is C(O)C 1-6 alk-C(O)C 1-6 alkoxy such as C(O)CH 2 C(O)CH 2 CH 3 . In yet other embodiments, R 8  is H. In still further embodiments, R 8  is SO 3 H. In other embodiments, R 7  is C(O)C 1-6 alk-C(O)C 1-6 alkoxy such as C(O)CH 2 C(O)CH 2 CH 3 . In still further embodiments, one or both of R 7  and R 8  are C(O)(optionally substituted heteroaryl) such as C(O)(optionally substituted pyridyl). In other embodiments, one or both of R 7  and R 8  are C(O)(optionally substituted C 1-6 alkyl) such as C(O)(C 1-6 alkyl substituted with C(O)O(C 1-6 alkyl) such as C(O)OCH 2 CH 3 ), C(O)-(substituted methyl), C(O)-(substituted t-butyl), C(O)-(optionally substituted ethyl), C(O)-(unsubstituted propyl), C(O)-(propyl substituted with alkyl, cycloalkyl, heteroaryl, heterocyclyl, alkoxy, aryloxy, OH, CN, or halide), C(O)-(optionally substituted n-butyl), C(O)-(optionally substituted i-butyl), C(O)-(optionally substituted pentyl), or C(O)-(optionally substituted hexyl). Thus, in this example, one of R 7  or R 8  is C(O)C 1-6 alk-C(O)C 1-6 alkoxy such as C(O)CH 2 C(O)OCH 2 CH 3  and the other is H. In other examples, R 7  and R 8  is C(O)C 1-6 alk-C(O)C 1-6 alkoxy such as C(O)CH 2 C(O)OCH 2 CH 3 . In further embodiments, one or both of R 7  and R 8  are C(O)-(optionally substituted aryl) such as C(O)-(phenyl substituted with alkyl, cycloalkyl, aryl, heteroaryl, heterocyclyl, alkoxy, aryloxy, OH, CN, or halide), C(O)-(substituted naphthyl), C(O)-(optionally substituted indanyl), C(O)-(optionally substituted indenyl), C(O)-(optionally substituted anthryl), C(O)-(optionally substituted phenanthryl), C(O)-(optionally substituted fluorenyl), C(O)-(optionally substituted 1,2,3,4-tetrahydronaphthalenyl), C(O)-(optionally substituted 6,7,8,9-tetrahydro-5H-benzocycloheptenyl), or C(O)-(optionally substituted 6,7,8,9-tetrahydro-5H-benzocycloheptenyl). For example one or both of R 7  and R 8  is C(O)(phenyl is substituted with CO 2 H). 
     In the structure of Formula (II), m and n are, independently, 0 to 4. In some embodiments, m and n are the same. In other embodiments, m and n differ. In further embodiments, m is 0. In yet other embodiments, n is 0. In still other embodiments, m and n are 1. In yet further embodiments, m and n are 2. In other embodiments, m and n are 3. In further embodiments, m and n are 4. 
     In some aspects, the compound of Formula (II) is not: 
     (i) 1H,1′H-[2,2′-biindole]-3,3′-diyl diacetate; 
     (ii) 3,3′-bis(phenylacetoxy)-2,2′-bi-indolyl; 
     (iii) 3,3′-bis(p-methoxyphenylacetoxy)-2,2′-bi-indolyl; 
     (iv) 3,3′-bis(1-napthylacetoxy)-2,2′-bi-indolyl; 
     (v) 3,3′-bis(phenylbutyryloxy)-2,2′-bi-indolyl; 
     (vi) 3,3′-bis(pivaloyloxy)-2,2′-bi-indolyl; 
     (vii) 3,3′-bis(1-adamantylcarbonyloxy)-2,2′-bi-indolyl; 
     (viii) 3,3′-bis(ethoxycarbonylacetoxy)-2,2′-bi-indolyl. 
     In further embodiments, preferred compounds encompassed by Formula (II) is of Formula (II-A) or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In this structure of Formula (II-A), each R C  is, independently, H, optionally substituted C 1-6 alkyl, optionally substituted C 3-6 cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl such as H, optionally substituted C 1-6 alkyl, or optionally substituted aryl. In some aspects, one R C  is H. In further aspects, both R C  are H. 
     In some embodiments, a preferred compound encompassed by Formula (II) is the following or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In further embodiments, a preferred compound encompassed by Formula (II) is of Formula (II-B) or a salt thereof. 
     
       
         
         
             
             
         
       
     
     In this structure of Formula (II-B), one or both R E  is H, optionally substituted C 1-6 alkyl, or optionally substituted heteroaryl, provided that both R E  are not H. In some aspects, one or both R E  is optionally substituted C 1-6 alkyl such as C 1-6 alkyl substituted with an ester. In other aspects, one R E  is optionally substituted C(O)C 1-6 alk-C(O)C 1-6 alkoxy such as C(O)CH 2 C(O)CH 2 CH 3  and the other is H. In further aspects, both R E  are optionally substituted C(O)C 1-6 alk-C(O)C 1-6 alkoxy such as C(O)CH 2 C(O)CH 2 CH 3 . In yet other aspects, one R E  is H. In further aspects, one or both R E  is optionally substituted heteroaryl such as optionally substituted pyridyl. In yet other aspects, one or both RE is substituted methyl, ethyl, propyl, n-butyl, substituted t-butyl, i-butyl, pentyl, or hexyl. In further aspects, one or both of R E  is substituted phenyl substituted with alkyl, cycloalkyl, aryl, heteroaryl, heterocyclyl, aryloxy, OH, CN, or halide; substituted naphthyl; optionally substituted indanyl; optionally substituted indenyl; optionally substituted anthryl; optionally substituted phenanthryl; optionally substituted fluorenyl; optionally substituted 1,2,3,4-tetrahydronaphthalenyl; optionally substituted 6,7,8,9-tetrahydro-5H-benzocycloheptenyl; or optionally substituted 6,7,8,9-tetrahydro-5H-benzocycloheptenyl. 
     Instill other embodiments, preferred compounds encompassed by Formula (II) are the following or a salt thereof. 
     
       
         
         
             
             
         
       
     
     The compounds discussed above may also be used in the form of salts derived from acceptable acids, bases, alkali metals and alkaline earth metals. Thus, the compounds described herein may exist as the free base or a salt thereof. Preferably, the salts are formed via ionic interactions, covalent interactions, or combinations thereof. For example, the salts may be formed by alkylating a heteroatom such as a N-atom within the compound and having a counteranion ionically bound to the heteroatom. The counteranion may be selected by those skilled in the art and includes those anions from the acids identified above and below. 
     The salts can be formed from organic and inorganic acids including, e.g., carboxylic acids such as acetic, propionic, lactic, citric, tartaric, succinic, fumaric, maleic, malic, malonic, mandelic, and phthalic acids, hydrochloric (Cl − ), hydrobromic (Br − ), hydroiodic (I − ), hydrofluoric (F − ), phosphoric, nitric, sulfuric, methanesulfonic, phosphoric, napthalenesulfonic, benzenesulfonic, toluenesulfonic, camphorsulfonic, and similarly known acceptable acids. In some embodiments, the salt is a sulfate salt, alkylsulfate salt, bisulfate salt, phosphate salt, halide salt, sulfite salt, or bisulfite salt. In further embodiments, the compounds are a sulfate salt. In other embodiments, the compound exists as an alkylsulfate salt such as a methylsulfate or ethylsulfate salt. In further embodiments, the compound exists as a halide salt such as an iodide salt, chloride salt, bromide salt, or fluoride salt. In other embodiments, the compound exists as a bisulfate salt. In yet further embodiments, the compound exists as a phosphate salt. 
     In other embodiments, salts may also be formed from inorganic bases, desirably alkali metal salts including, e.g., sodium, lithium, or potassium, such as alkali metal hydroxides. Examples of inorganic bases include, without limitation, sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide. 
     Salts may also be formed from organic bases, such as ammonium salts, mono-, di-, and trimethylammonium, mono-, di- and triethylammonium, mono-, di- and tripropylammonium, ethyldimethylammonium,benzyldimethylammonium,cyclohexylammonium,benzyl-anmonium, dibenzylammonium, piperidinium, morpholinium, pyrrolidinium, piperazinium, 1-methylpiperidinium, 4-ethylmorpholinium, 1-isopropylpyrrolidinium, 1,4-dimethylpiperazinium, 1 n-butyl piperidinium, 2-methylpiperidinium, 1-ethyl-2-methylpiperidinium, mono-, di- and triethanolammonium, ethyl diethanolammonium, n-butylmonoethanolammonium, tris(hydroxymethyl)methylammonium, phenylmono-ethanolammonium, diethanolamine, ethylenediamine, choline, betaine, carnitine, and the like. In one example, the base is selected from among sodium hydroxide, lithium hydroxide, potassium hydroxide, and mixtures thereof. 
     The compounds discussed herein may also encompass tautomeric forms of the structures provided herein, where such forms may be formed. 
     Embodiments of modified indigo compounds that have been found particularly useful for the dyeing of textile yarns are those that comprise an indigo compound in which at least one of the amine groups is functionalized with an amido-pyridine or a salt thereof. For example, in some embodiments, the modified indigo compound may be selected from a compound having the following base structure, or a salt thereof. 
     
       
         
         
             
             
         
       
     
     By the compound having the above-shown base structure, it is meant that each position in the above structure may include additional unshown substituents. For instance, in some embodiments, the nitrogen atom of each pyridine ring may comprise an alkane substituent, such as a methyl group, an ethyl group, or a propyl group, which is represented by R1 and R2 in the structure below. In some embodiments, the salt is formed by the nitrogen atom of the each pyridine ring acting as an anion, with the cation being selected from the group consisting of the halogens (e.g. chlorine, bromine, iodine, methyl chloride, and the like) and the sulfates, such as methyl sulfate, ethyl sulfate, and the like. For example, the anion may comprise one of the following structures. 
     
       
         
         
             
             
         
       
     
     Particularly preferred modified indigo compound salts are shown below. 
     
       
         
         
             
             
         
       
     
     In addition to being readily convertible to indigo by the mechanisms described herein, each of these compounds has been found to have a particularly beneficial combination of oxygen stability, water stability, and water solubility that make them particularly suitable for dyeing as described herein. 
     In some embodiments, a bridge may link the pyridine ring with the rest of the modified indigo compound. For example, in some embodiments, the modified indigo compound may be selected from a compound having the following base structure, or a salt thereof: 
     
       
         
         
             
             
         
       
     
     in which R 3′  and R 4′  may be an alkyl group, such as methyl, ethyl, propyl, or the like, or an alkoxide group. By the compound having the above-shown base structure, it is meant that each position in the above structure may include additional unshown substituents. Moreover, in the above structure, the nitrogen atom of each pyridine ring may comprise an alkane substituent, such as a methyl group, an ethyl group, or a propyl group, which is represented by R 1′  and R 2′ . In other embodiments, R 1′  and R 2′  in the above structure may simply be hydrogen. In some embodiments, the salt may be formed by the nitrogen atom of each pyridine ring acting as an anion, with the cation being selected from the group consisting of the halogens (e.g. chlorine, bromine, iodine, methyl chloride, and the like) and the sulfates, such as methyl sulfate, ethyl sulfate, and the like. 
     In contrast to the structures described above, in which the nitrogen atom of the pyridine ring is in the 3 position, the nitrogen atom of the pyridine ring may also be located in either the 2 or 4 positions. In some embodiments, for instance, the modified indigo compound may be selected from a compound having the following base structure, or a salt thereof: 
     
       
         
         
             
             
         
       
     
     As with the above, by the compound having the above-shown base structure, it is meant that each position in the above structure may include additional unshown substituents. For instance, in some embodiments, the nitrogen atom of each pyridine ring may comprise an alkane substituent, such as a methyl group, an ethyl group, or a propyl group, which may be represented by R 1′  and R 2′  in the above structure. In other embodiments, R 1′  and R 2′  in the above structure may simply be hydrogen. Moreover, in some embodiments, the bridge linking the pyridine ring with the rest of the modified indigo compound represented by R 3′  and R 4′  in the above structure may be lacking. 
     In other embodiments, R 3′  and R 4′  may be an alkyl group, such as methyl, ethyl, propyl, or the like, or an alkoxide group. In some embodiments, the salt is formed by the nitrogen atom of each pyridine ring acting as an anion, with the cation being selected from the group consisting of the halogens (e.g. chlorine, bromine, iodine, methyl chloride, and the like) and the sulfates, such as methyl sulfate, ethyl sulfate, and the like. For example, in some embodiments, the modified indigo compound may be selected from the following salts: 
     
       
         
         
             
             
         
       
     
     In contrast to the structures described above, in which the nitrogen atom of the pyridine ring is in the 2, 3, or 4 positions, the nitrogen atom of the pyridine ring may also be located in either the 1 or 5 positions. In some embodiments, for instance, the modified indigo compound may be selected from a compound having the following base structure, or a salt thereof: 
     
       
         
         
             
             
         
       
     
     Again, by the compound having the above-shown base structure, it is meant that each position in the above structure may include additional unshown substituents. For instance, in some embodiments, the nitrogen atom of each pyridine ring may comprise an alkane substituent, such as a methyl group, an ethyl group, or a propyl group, which may be represented by R 1′  and R 2′  in the above structure. In other embodiments, R 1′  and R 2′  in the above structure may simply be hydrogen. Moreover, in some embodiments, the bridge linking the pyridine ring with the rest of the modified indigo compound represented by R 3′  and R 4′  in the above structure may be lacking. In other embodiments, R 3′  and R 4′  may be an alkyl group, such as methyl, ethyl, propyl, or the like, or an alkoxide group. 
     II. METHODS OF PRODUCTION 
     The compounds described above may be prepared by known chemical synthesis techniques. Among such preferred techniques known to one of skill in the art are included the synthetic methods described in conventional textbooks relating to the construction of synthetic compounds. 
     The above compounds comprising an indigo compound in which at least one of the amine groups is functionalized with an amido-pyridine or a salt thereof may generally be prepared according to Schemes 1-3. 
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     In some embodiments, it may be desirable to dry the modified indigo compound at the conclusion of this process, so as to remove all or substantially all of the water. In doing so, one may prepare a powder comprising the modified indigo compound. This powder may be easily shipped and stored and will not convert to indigo during shipping and/or storage. Moreover, the powder may easily be dissolved at the mill to form the dye. Alternatively, the modified indigo compound may be added to a non-aqueous solvent for shipping and/or storage. 
     In some embodiments, the modified indigo compound may be prepared at the mill at which the dyeing occurs and/or immediately before the dyeing process. For instance, in some embodiments, one or more steps in the preparation process may be performed immediately prior to use of the modified indigo compound for dyeing. As an example, the following compound: 
     
       
         
         
             
             
         
       
     
     may be prepared by contacting the base structure (represented by the following: 
     
       
         
         
             
             
         
       
     
     with an acid, such as hydrochloric acid. Such a step could easily be performed at the mill and immediately prior to use. This may be particularly beneficial where, for example, the intermediate structure may be more stable and/or easier to store than the modified indigo compound that is used in the dyeing process. 
     III. COMPOSITIONS CONTAINING THE COMPOUND 
     Compositions useful herein, in one embodiment, contain a compound discussed above. In some embodiments, the compositions are in the form of a foam. In other embodiments, the compositions are in the form of a spray comprising a diluent. 
     When the dye compounds are utilized in methods of foam dyeing, they are applied to a substrate in the form of a foam. In some embodiments, the foam contains about 0.1 to about 50 wt. %, based on the weight of the foam, of the dye compound. In other embodiments, the foam contains about 1 to about 50 wt. %, about 2 to about 30 wt. %, about 5 to about 45 wt. %, about 10 to about 50 wt. %, about 20 to about 40 wt. %, about 5 to about 40 wt. %, about 5 to about 30 wt. %, about 10 to about 30 wt. %, based on the weight of the foam, of the dye compound. 
     The foams contain water, a dye molecule discussed herein, and a gas. In some embodiments, the water in the foam is acidic. In other embodiments, the foam contains a foaming agent that may be selected by one skilled in the art. For example, the foaming agent may be a nonionic, anionic, cationic, zwitterionic, or amphoteric surfactant. Desirably, the foaming agent is present in an amount to provide a stable foam that delivers the dye compound to the substrate and breaks down after application to the substrate. 
     The term “stable” as used herein to refer to the foam refers to the ability of the foam to maintain its original form from the instrument that disperses the foam until it comes into contact with the substrate. Similarly, the term “breaks down” refers to the gas dispersing from the foam and foam being reduced to the original components. One of skill in the art would be able to judge when a foam is stable and when it has broken down. 
     A variety of gases may be utilized to form the foam. Desirably, the foam is inexpensive and includes air. Other gases include, without limitation, oxygen, nitrogen, argon, carbon dioxide, or any combinations thereof. In some embodiments, the gas contains at least about 10%, 20%, 30%, 40 wt. %, or more of oxygen and thus couldn&#39;t be used in typical dyeing methods in the art. In some embodiments, the foam contains about 60 to about 95 wt. %, about, 70 to about 95 wt. %, about 80 to about 95 wt. %, about 60, 65, 70, 75, 80, 85, 90, or wt %, based on the weight of the foam, of a gas. 
     The dye compounds may also be applied to a substrate in the form of a spray. The sprays discussed herein, thus, contain a diluent and a dye compound. The term “diluent” as used herein refers to a liquid compound that is capable of solubilizing some or all of the compounds discussed herein. In some embodiments, the diluent is water. In further embodiments, the diluent contains acidic water. In other embodiments, the diluent contains water and an organic solvent such as low vapor pressure organic solvents. In further embodiments, the diluent contains an organic solvent. Examples of organic solvents include, without limitation, glycols such as diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, propylene glycol, alcohols such as glycerol, ketones, amines, or combinations thereof. 
     The sprays contain about 60 to about 95 wt. %, based on the weight of the spray, of water. In some embodiments, the sprays contain about 60 to about 90 wt. %, about 70 to about 90 wt. %, about 80 to about 90 wt. %, about 70 to about 80 wt. %, about 60 to about 80 wt. %, based on the weight of the spray, of water. 
     When the dye compounds are utilized in methods of spray dyeing, the spray contains about 0.1 to about 50 wt. %, based on the weight of the spray, of the dye compound. In other embodiments, the spray contains about 1 to about 50 wt. %, about 2 to about 30 wt. %, about 5 to about 45 wt. %, about 10 to about 50 wt. %, about 20 to about 40 wt. %, about 5 to about 40 wt. %, about 5 to about 30 wt. %, about 10 to about 30 wt. %, based on the weight of the spray, of the dye compound. 
     The foams or sprays may also include optional suitable inert or inactive ingredients that are useful in dye foams or sprays for dyeing substrates. The foams or sprays may further include standard dyeing chemicals such as those described in Denim, Manufacture, Finishing and Applications, 1st Edition, Ed.: Roshan Paul, Woodhead Publishing, Apr. 23, 2015; Handbook of Textile and Industrial Dyeing, Principles, Processes and Types of Dyes, 1st Edition, Ed.: M. Clark, Woodhead Publishing, Oct. 25, 2011; and Handbook of Textile and Industrial Dyeing, Volume 2: Applications of Dyes, 1st Edition, Ed.: M. Clark, Woodhead Publishing, Oct. 25, 2011, all of which are incorporated herein by reference. 
     In some embodiments, the standard dyeing chemicals prepare the substrate for dyeing, i.e., a pretreating step. In other embodiments, the standard dyeing chemicals are useful in the step of dyeing the substrate. In further embodiments, the standard dyeing chemicals are useful in dyeing denim. In yet other embodiments, the standard dyeing chemicals are useful after dyeing is complete, i.e., a post-treating step such as a hydrolyzing step, neutralizing step, or a rinsing step. These compounds may be included in the foam or spray and include, without limitation, one or more of an acid, cationic agent, chelating agent, color retention agent, coloring agent, dispersant, foaming agent, mercerization reagent, penetration enhancer, pH buffering agent, salt, stabilizing agent, solubilizing agent, surfactant, thickening agent, tracer, viscosity modifier, or wetting agent. One of skill in the art would be able to determine if a standard dyeing chemical may be used before, during, or after dyeing the substrate. 
     In other embodiments, the foams or sprays contain a cationic agent. In some embodiments the cationic agent is an ammonium salt such as diallyldimethylammonium chloride, polymerized diallyldimethylammonium chloride, [2-(acryloyloxy)ethyl] trimethylammonium chloride, 3-chloro-2-hydroxylpropyl trimethyl-ammonium chloride, or combinations thereof. 
     The foams or sprays may further comprise a solubilizing agent. In some embodiments, the solubilizing is an organic solvent, surfactant, or emulsifier. In other embodiments, the organic solvent is a low vapor pressure organic solvent. Examples of organic solvents include, without limitation, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, propylene glycol, glycerol, or combinations thereof. In further embodiments, the surfactant is glyceryl monostearate, polyoxoethylated castor oil, polysorbates such as the Tween® surfactants, sodium lauryl sulfate, sodium dodecyl sulfate, sorbitan esters such as the Span® or Arlacel™ surfactants, stearyl alcohols, cetyl alcohols, triethanolamine, or the Triton™ X-100 surfactant, among others. 
     The foam or spray may also contain a stabilizing agent. Such agents may be selected by those skilled in the art and include, without limitation, NaCl, Na 2 SO 4 , a surfactant, or combinations thereof. In some embodiments, the surfactant is glyceryl monostearate, polyoxoethylated castor oil, polysorbates such as the Tween® surfactants, sodium lauryl sulfate, sodium dodecyl sulfate, sorbitan esters such as the Span® or Arlacel™ surfactants, stearyl alcohols, cetyl alcohols, triethanolamine, or the Triton™ X-100 surfactant, among others 
     IV. METHODS OF USING THE COMPOUNDS 
     The methods of foam and spray dyeing described herein are practical and feasible. Thus, the indigo dyeing methods reduce cost, increase throughput and improve the sustainability of the denim-dyeing process. In fact, the compounds discussed herein may be utilized in existing foam and spray dyeing plants in place of the currently utilized leuco-indigo methods with little to no change required for the mechanical equipment. 
     In some embodiments of the present disclosure, the process of indigo foam or spray dyeing with a modified indigo compound involves two basic steps. In a first step, a substrate such as a textile yarn is contacted with a dye solution that contains a modified indigo compound. As a result of this contact, the substrate takes up an amount of the modified indigo compound. For example, when a cotton yarn is contacted with the dye solution, the dye solution both coats a surface of the yarn and penetrates some distance below the surface of the yarn. The amount of dye solution contained within the resulting yarn may be controlled by controlling the duration of the contact, the amount of foam/spray, the pressure with which it is applied and the concentration of modified indigo in the dye solution. 
     In other embodiments of the present disclosure, the substrate is pretreated with a resist so as to prevent the dye from contacting and diffusing into the yarn. The resist could be applied to create desired design characteristics 
     The methods are useful in dyeing a substrate by contacting one or more compound described herein with the substrate. The methods are also used in dyeing a substrate by contacting one or more of the compounds described herein or the following compounds with the substrate: 
     (i) N,N′-dinicotinoyl-[2,2′-biindolinylidene]-3,3′-dione; 
     (i) the N″,N″′-methylpyridinium bis(methylsulfate) salt of N,N′-dinicotinoyl-[2,2′-biindolinylidene]-3,3′-dione; 
     (iii) N,N′-diacetyl-[2,2′-biindolinylidene]-3,3′-dione; 
     (iv) N,N′-dipropionyl-[2,2′-bi-indolinylidene]-3,3′-dione; 
     (v) N,N′-di-isobutyryl-[2,2′-biindolinylidene]-3,3′-dione; 
     (vi) N,N′-dipivaloyl-[2,2′-biindolinylidene]-3,3′-dione; 
     (vii) N,N′-bis(cyclohexylcarbonyl)-2,2′-bi-indolinylidene-3,3′-dione; 
     (viii) N,N′-bis(3-phenylpropionyl)-2,2′-bi-indolinylidene-3,3′-dione; 
     (ix) N,N′-bis(ethoxycarbonylacetyl)-2,2′-bi-indolinylidene-3,3′-dione; 
     (x) N,N′-bis(2-phenylacetyl)-[2,2′-bi-indolinylidene]-3,3′-dione; 
     (xi) N,N′-bis-(p-methoxyphenylacetyl)2,2′-bi-indolinylidene-3,3′-dione; 
     (xii) N,N′-bis(1-naphthylacetyl)-2,2′-bi-indolinylidene-3,3′-dione; 
     (xiii) N,N′-bis(2-phenylbutyryl)-2,2′-indolinylidene-3,3′-dione; 
     (xiv) (E)-1,1′-di(adamantane-1-carbonyl)-[2,2′-biindolinylidene]-3,3′-dione. 
     (xv) 1H,1′H-[2,2′-biindole]-3,3′-diyl diacetate; 
     (xvi) 3,3′-bis(phenylacetoxy)-2,2′-bi-indolyl; 
     (xvii) 3,3′-bis(p-methoxyphenylacetoxy)-2,2′-bi-indolyl; 
     (xviii) 3,3′-bis(1-napthylacetoxy)-2,2′-bi-indolyl; 
     (xix) 3,3′-bis(phenylbutyryloxy)-2,2′-bi-indolyl; 
     (xx) 3,3′-bis(pivaloyloxy)-2,2′-bi-indolyl; 
     (xxi) 3,3′-bis(1-adamantylcarbonyloxy)-2,2′-bi-indolyl; or 
     (xxii) 3,3′-bis(ethoxycarbonylacetoxy)-2,2′-bi-indolyl. 
     The term “substrate” as used herein refers to a material that may be dyed using the compounds described herein. The substrate contains natural substrates, synthetic substrates, or combinations thereof. In some embodiments, the substrate is natural. In other embodiments, the substrate is synthetic. In further embodiments, the substrate contains natural and synthetic components. The natural substrate may be selected by those skilled in the art from, without limitation, plant or animal substrates. Plant fibers include cotton, kapok, hemp, bamboo, flax, sisal, jute, kenaf, ramie, bamboo, soybean, or coconut, among others. Animal substrates include silk, wool, leather, hair, feather, among others. In some embodiments, the animal substrate is silk, wool, leather, or feather. In other embodiments, the substrate comprises a synthetic fiber such as a synthetic polymer. The synthetic substrate may be prepared using viscose or lyocel processes, preferably or from regenerated/spun cellulose processes. Thus, the synthetic substrate includes, without limitation, rayon such as lyocel (TENCEL®), a polyamide such as nylon, polyester, polyacrylate, polyolefin, or spandex. In some embodiments, the synthetic substrate is a polyamide such as nylon. In other embodiments, the polyester is polyethylene terephthalate. In further embodiments, the polyolefin is polypropylene or polyethylene. In still other embodiments, the polyacrylate is a copolymer of polyacrylonitrile. In contrast to the methods used in the art for dyeing synthetic substrates, the methods described herein do not require heating the substrate, e.g., to the substrate&#39;s T g , during the dyeing process. 
     While the present disclosure is primarily described in relation to the dyeing of cotton yarn, it should be understood that the modified indigo compounds and dyeing processes disclosed herein may also be used to dye any number of different textile materials, including without limitation fibers comprising cellulosic material, such as silk, wool, rayon, lyocel, flax, linen, ramie, and the like, as well as materials comprising combinations thereof. 
     The substrate may be in any physical form or shape that permits dyeing by the compounds described herein. Thus, the substrate may be a single fiber or a number of fibers gathered together in another form. In some embodiments, the substrate is in the form of a yarn, sheet, or package. In other embodiments, the substrate is a yarn. In further embodiments, the substrate is a package. In other embodiments, the substrate is a fabric. The yarns may be fitted together to form sheets or packages of yarns such as a carpet. Similarly, the fibers may be woven to form a sheet such as a textile. In some embodiments, the dye substrate or textile is denim. In further embodiments, the substrate is a fabric or textile such as clothing or garment. 
     As used herein, the term “yarn” should be understood as meaning a length of interlocked textile fibers or filaments that is suitable for the production of fabrics. In some embodiments, indigo-dyeing is performed on yarn or ropes of yarn. In other embodiments, the yarn is converted to packages, which can be used in weaving or knitting operations. For example, indigo-dyed yarn is often weaved into denim fabric, and more specifically this dyed yarn is then used as the warp yarn in a denim fabric weave. However, in some processes the yarn may be weaved into a fabric, such as through a denim weave, and then dyed. Accordingly, unless specified, the term yarn should be understood herein as inclusively referring to any of individual yarns, ropes of yarn, packages of yarn, sheets of yarn, and yarn that is present in a fabric. 
     Moreover, as used herein, the term “cotton yarn” should be understood as any yarn containing cotton fibers. In some embodiments, the cotton yarn may contain 100% cotton fibers. In other embodiments, the cotton yarn may contain a mixture of cotton fibers and other natural or synthetic fibers/filaments. For example, the cotton yarn may contain a blend of cotton and polyester, nylon, elastomeric materials such as elastane (i.e. spandex), or mixtures thereof. Additionally, in some embodiments, a portion of the cotton or all of the cotton may be treated. For example, in some embodiments at least a portion of the cotton may be treated so as to render the cotton hydrophobic. Accordingly, unless specified, the term cotton yarn should be understood herein as inclusively referring to any yarn that contains cotton fibers, including mixtures of cotton and other materials. 
     The term “contacting” as used herein refers to any route by which the substrate is contacted with the dye compound. In some embodiments, the substrate is contacted with a foam comprising the dye compound. In further embodiments, the substrate is contacted with an aqueous foam or spray comprising the dye compound. In still further embodiments, the dye compound is in the form of a foam and the foam is applied to the substrate for example by spraying the substrate with the foam. In other embodiments, the foam is applied to the substrate in a foam application as described in U.S. Pat. No. 8,215,138, which is hereby incorporated by reference, but in the absence of a hermitically sealed chamber, inert atmosphere, or combination thereof. 
     In yet other embodiments, the substrate is sprayed with a spray comprising the dye compound. One of skill in the art would understand that spray application to a substrate includes a contacting step where droplets (Water in air) are applied to the substrate. Suitable techniques include those described in, for example, http://www.rotaspray.com/resources/ITMA+RotaSpray_ORTA_DTSTAR+flyer.pdf. Simply state, the spray containing the dye compound may be applied to the substrate using a spray nozzle at a pressure that may be selected by those skilled in the art. 
     Advantageously, the foam or spray containing the dye compound lacks a reducing agent to convert the compound to a leuco form of the compound. In other embodiments, the foam or spray containing the dye compound lacks an alkali agent. In further embodiments, the or spray containing the dye compound lacks a reducing agent which is sodium hydrosulfite formamidine sulfinic acid, glucose, sodium borohydride, sodium metabisulfite, thiourea dioxide cellobiose, glyceraldehyde, or fructose. 
     When an aqueous foam or spray is utilized to dye the substrate, it is prepared by mixing one or more compound with water. In some embodiments, each foam or spray comprises about 0.5 wt. % to about 70 wt. %, based on the weight of the foam or spray, of the compound. In other embodiments, the foam or spray comprises about 1 wt. % to about 50 wt. %, based on the weight of the foam or spray, of the compound. In further embodiments, the foam or spray comprises about 2 wt. % to about 30 wt. %, based on the weight of the foam or spray, of the compound. In still other embodiments, the foam or spray contains about 5 to about 25 wt. %, based on the weight of the foam or spray, of the compound. In yet further embodiments, the foam or spray contains about 10 to about 20 wt. %, based on the weight of the foam or spray, of the compound. In other embodiments, the foam or spray contains about 12 to about 18 wt. %, based on the weight of the foam or spray, of the compound. In further embodiments, the foam or spray contains about 14 to about 16 wt. %, based on the weight of the foam or spray, of the compound. Preferably, the foam or spray contains about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 wt. %, based on the weight of the foam or spray, of the compound. More preferably, each foam or spray contains about 1 to about 3 wt. % to about 70 wt. %, based on the weight of the foam or spray, of the compound. Even more preferably, each foam or spray contains about 2 wt. % to about 70 wt. %, based on the weight of the foam or spray, of the compound. 
     In addition to the compound and water, the aqueous foam or spray may contain other additional components such as those described above for foams or sprays containing the compound. These compounds include, without limitation, an acid, cationic agent, caustic agent, chelating agent, color retention agent, coloring agent, dispersant, foaming agent, hydrolyzing agent, mercerization reagent, penetration enhancer, pH buffering agent, salt, solubilizing agent, stabilizing agent, surfactant, thickening agent, tracer, viscosity modifier, wetting agent, or combinations thereof. One of skill in the art would be able to determine if a standard dyeing chemical may be used before, during, or after dyeing the substrate. In some embodiments, the aqueous foam or spray lacks a solubilizing agent. In other embodiments, the aqueous foam or spray contains solubilizing agent. In further embodiments, the aqueous foam or spray is acidic, i.e., has a pH of less than about 7. In some embodiments, the aqueous foam or spray as a pH of about 0.5 to about 7, about 1 to about 7, about 1 to about 6, about 1 to about 5, about 1 to about 4, about 1 to about 3, about 1 to about 2, about 1, about 2, about 3, about 4, about 5, about 6, or about 6. 
     The substrate is kept in contact with the aqueous solution, i.e., dyed, for a time sufficient so as to dye the substrate. In some embodiments, the time is dependent on the extent of dye that penetrates the substrate. In other embodiment, the time is dependent on the desired color of the substrate is achieved. In further embodiments, the time is dependent on the concentration of the dye being applied to the substrate. In yet other embodiments, the substrate is kept in contact with the aqueous solution for about 5 seconds to about 10 hours. In still further embodiments, the substrate is kept in contact with the dye compound for about 5, 10, 20, 30, or 45 seconds, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 30, or 45 minutes, or 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 hours. 
     The substrate also is kept in contact with the aqueous solution at a suitable temperature. In some embodiments, the dyeing temperature is any temperature that does not degrade any components of the dyeing process. In some embodiments, the temperature is ambient temperature. In other embodiments, the temperature is about 20 to about 40° C., such as about 10 to about 35° C., or about room temperature. 
     In another step, the modified indigo compound that has been taken up by the dye-treated substrate is converted to indigo through a process of hydrolysis. In some embodiments, the substrate is contacted with a hydrolyzing agent, the hydrolyzing agent being capable of reacting with the modified indigo compound contained within the substrate to convert the modified indigo compound into indigo. For example, when a cotton yarn that has been contacted with a dye solution is then contacted with an appropriate hydrolyzing agent, the modified indigo contained within the cotton yarn is converted to indigo, thereby producing an indigo-dyed yarn. 
     The hydrolysis is performed using any chemical compound or condition that is capable of converting the dye compound to indigo. In some embodiments, the hydrolysis is performed in aqueous compositions which contain a hydrolyzing agent. In other embodiments, the hydrolyzing agent may be selected by one skilled in the art and may include, without limitation, a base, heat, steam, or a combination thereof. 
     In some embodiments, the substrate may be contacted with an alkali agent in order to hydrolyze the modified indigo compound so as to convert it into indigo. The contacting of the substrate with the alkali hydrolyzing agent may be performed in a number of different manners. By converting the modified indigo compound into indigo, an indigo-dyed substrate is produced. 
     In other embodiments, hydrolysis of the dye compound is performed with a solution which contains water. In other embodiments, hydrolysis is performed with water. The water can be from a fresh source or may be reused. Thus, the water can contain other components including, without limitation, an acid, cationic agent, chelating agent color retention agent, coloring agent, dispersant, foaming agent, mercerization reagent, organic solvent, pH buffering agent, penetration enhancer, salt, stabilizing agent, solubilizing agent, surfactant, thickening agent, tracer, viscosity modifier, or wetting agent. In some embodiments, the rinse water contains an acid, cationic agent, chelating agent, dispersant, foaming agent, organic solvent, pH buffering agent, penetration enhancer, salt, solubilizing agent, surfactant, thickening agent, tracer, viscosity modifier, or wetting agent. 
     In further embodiments, the hydrolyzing agent is an alkali agent. In some embodiments, the alkali agent is applied in the form of a foam or a spray. In other embodiments, the alkali agent is applied in the form of a spray. Preferably, the alkali agent ensures that the pH of the hydrolysis is raised to greater than about 11. For example, the base is an oxide, hydroxide of alkali metals or alkaline earth metal, or carbonate of an alkali or alkaline earth metal. In some embodiments, the hydrolysis is performed with an oxide. In other embodiments, the hydrolysis is performed with a hydroxide of an alkali metal such as sodium hydroxide, potassium hydroxide, or lithium hydroxide. In further embodiments, the hydrolysis is performed with a carbonate such as sodium carbonate or potassium carbonate. In still other embodiments, the hydrolysis is performed with a hydroxide of an alkaline earth metal. In some embodiments, the hydrolyzing foam or spray contains about 2 to about 25 wt. %, about 5 to about 20 wt. %, about 5 to about 15 wt. %, about 10 to about 25 wt. %, based on the weight of the hydrolyzing foam or spray, of the hydrolyzing agent. 
     The hydrolysis may also be performed using an elevated temperature such as heat or steam. Thus, in some embodiments, the hydrolysis may be performed using heat such as by contacting the dyed substrate with a heat plate or blowing hot air on the dyed substrate. One skilled in the art would be able to select a suitable temperature for use in the hydrolysis of the dye compound. For example, the heat comprises a temperature of at least about 40° C. In some embodiments, the heat comprises a temperature of about 40 to about 200° C. In other embodiments, the heat comprises a temperature of about 40 to about 80° C. In further embodiments, the heat comprises a temperature of about 40 to about 70° C. In still further embodiments, the heat comprises a temperature of about 80 to about 200° C., such as about 100 to about 200° C., about 120 to about 200° C., about 150 to about 200° C., about 180 to about 200° C., about 80 to about 100° C., about 80 to about 120° C., about 80 to about 140° C., about 80 to about 160° C., about 80 to about 180° C., or about 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or about 200° C. 
     Similarly, steam may be used to effect the hydrolysis. In some embodiments, steam is sprayed onto the dyed substrate or the dyed substrate is passed through a unit comprising an atmosphere of steam. The temperature of the steam is desirably at a temperature recited above. 
     In many dyeing processes, multiple iterations of this two-step process will be necessary in order to obtain a desirable shade of indigo. Accordingly, in many dyeing processes, once the modified indigo compound on the substrate is converted into indigo, the substrate will again be contacted with dye solution containing a modified indigo compound. In some embodiments, the substrate is contacted with the same foam or spray that was used to as the initial dye foam or spray. In other embodiments, the substrate is contacted with another dye foam or spray containing the same or a different amount of the dye compound. One of skill in the art would be able to determine how many instances it is necessary to contact the substrate with the dye compound. See, for example, Denim, Manufacture, Finishing and Applications, 1st Edition, Ed.: Roshan Paul, Woodhead Publishing, Apr. 23, 2015; Handbook of Textile and Industrial Dyeing, Principles, Processes and Types of Dyes, 1st Edition, Ed.: M. Clark, Woodhead Publishing, Oct. 25, 2011; and Handbook of Textile and Industrial Dyeing, Volume 2: Applications of Dyes, 1st Edition, Ed.: M. Clark, Woodhead Publishing, Oct. 25, 2011, all of which are incorporated herein by reference for these teachings. Although the substrate may only require contacting it once with the dye compound, the substrate typically is contacted with the dye compound at least two times. In some embodiments, the dye compound is contacted about 4 to about 25 times, about 5 to about 20 times, about 6 to about 18 times, about 7 to about 16 times, about 8 to about 14 times, about 8 to about 12 times, about 8 to 10 times, about 9 to 16 times, about 9 to about 14 times, about 9 to about 12 times, about 12 to about 18 times, about 12 to about 16 times, 1 to about 25 times, 2 to about 20 times, about 3 to about 18 times, about 4 to about 16 times, about 5 to about 15 times, about 5 to about 12 times, about 5 to about 10 times, about 5 to about 8 times, or any other ranges there between. 
     After the hydrolysis is complete, additional dyeing steps and hydrolysis steps may be utilized until the desired dye penetration or color is attained by the substrate. It may also be desirable to dry the dyed substrate prior to hydrolyzing. Thus, in some embodiments, the substrate is dyed as described herein, dried, and hydrolyzed as described herein. In some embodiments, the dyeing step is repeated 1 to about 50, 2 to about 30, 5 to about 25, 10 to about 20, or 1 to about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 times. Similarly, the hydrolysis step may be repeated the same number of times that the dyeing step is repeated. In some embodiments, the hydrolysis is repeated 1 to about 50, 2 to about 30, 5 to about 25, 10 to about 20, or 1 to about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 times. 
     Following dyeing and hydrolyzing, the substrate may be rinsed using techniques known to those skilled in the art. Similarly, the rinsing step may be performed between one or more of the dyeing and hydrolyzing steps. Preferably, one or more rinsing steps are performed after all dyeing and hydrolyzing steps are complete. However, in embodiments where the hydrolysis is performed using heat, such as an iron, hot air, or steam, a rinsing step may not be required. In situations where a rinsing step is performed, it may be is repeated 1 to about 50, 2 to about 30, 5 to about 25, 10 to about 20, or 1 to about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 times. 
     Desirably, the rinsing is performed using an aqueous solution. In some embodiments, the aqueous rinsing solution contains water. In other embodiments, the aqueous rinsing solution contains water and additional components such as organic solvents including those described herein. In further embodiments, the aqueous rinsing solution comprises a neutralization agent. The term “neutralization agent” as used herein refers to a chemical compound that neutralizes the hydrolyzing agent, if used. For example, the neutralization agent adjusts the pH of the dyed substrate to a pH of about 5 to about 9, e.g., about 6 to about 8, about 6 to about 7, about 6, 6.5, 7, 6.5 7, 7.5, 8, 8.5, or 9. In some examples, the neutralization agent is an acid or a base, as determined by the pH of the rinsate solution. In other examples, the neutralization agent is an acid such as acetic acid. In further examples, the neutralization agent is a base such as ammonia. In still other examples, the neutralization agent is pH adjusted water. In further embodiments, the aqueous rinsing solution contains buffering agent. 
     The dyeing is performed until the desired color of the substrate is reached. The desired color may be determined by one skilled in the art using techniques and instruments such as color spectrophotometers. 
     Before the substrate is again contacted with the dye solution, however, it may be desirable to rinse the indigo-dyed substrate to remove any residual hydrolyzing agent. Removal of residual hydrolyzing agent serves to prevent contamination of the dye solution with the hydrolyzing agent, which would decrease the effectiveness of the dye foam or spray. Accordingly, in some embodiments, the process may include a third step, the third step being rinsing the indigo dyed yarn to remove any residual hydrolyzing agent. The rinsing step may comprise simply contacting the indigo-dyed yarn with water. Alternatively, where an alkali hydrolyzing agent is employed, the rinsing step may comprise contacting the indigo-dyed yarn with an agent that is capable of neutralizing the hydrolyzing agent, such as a mildly acidic agent. 
     In some embodiments, hydrolyzing the modified indigo compound may comprise subjecting the dye-treated substrate to a heat treatment at an elevated temperature. For example, the dye-treated substrate may be subjected to elevated temperatures of greater than 60° C., alternatively greater than 80° C., alternatively greater than 100° C. It is noted that the substrate itself need to obtain the stated temperature, but rather that the substrate be subjected to the elevated temperature for a period of time sufficient to bring about conversion of the modified indigo compound into indigo. To increase the speed at which hydrolysis occurs, the heat treatment may also comprise contacting the dye-treated yarn with a moisture-rich atmosphere. For example, in some embodiments the dye-treated yarn may be contacted with steam. The application of heat (and optionally moisture, e.g. steam) to the dye-treated yarn triggers the hydrolysis of the modified indigo compound, decreasing the time necessary for conversion to indigo to occur. In some embodiments, for example, the application of heat (e.g. air heat, contact heat, etc.) and optionally moisture may be controlled to convert the modified indigo compound into indigo in less than fifteen minutes, alternatively less than ten minutes, alternatively less than eight minutes, alternatively less than six minutes, alternatively less than five minutes, alternatively less than three minutes. 
     In embodiments of the present process, the leuco-indigo dye composition may be replaced with a dye foam or spray containing a modified indigo compound according to the various embodiments described herein. For instance the dye foam or spray may generally comprise an aqueous solution of the modified indigo compound. In addition to water and the modified indigo compound, the dye foam or spray may also contain one or more of the following: wetting agents, thickening agents, chelating agents, pH buffering agents, and stabilizers. Notably, as described above, in many embodiments the dye foam or spray containing the modified indigo compound may not contain a reducing agent. In some embodiments, therefore, the dye foam or spray may consist essentially of water and the modified indigo compound. Additionally, because the modified indigo compound does not require strong reducing agents and a high pH environment to maintain stability, embodiments of the dye foam or spray may have a pH of less than 9, alternatively less than 8, alternatively less than 7. In some embodiments, it may be desirable that the dye foam or spray be about neutral, i.e. have a pH of about 7. 
     Additionally, rather than simply exposing the dye-treated yarns to air, the dye-treated yarn may be subjected to a treatment that is effective to more efficiently convert the modified indigo compound into indigo, such as those described herein. Importantly, the one or more yarns may continuously through a series of dye foams or sprays in order to obtain a desired shade of indigo in much the same way as in the conventional process. Accordingly, it is believed that large-scale commercial dyeing equipment might easily be converted to utilize the improved dyeing process disclosed herein without the need for major expenditures of capital. 
     In some embodiments, the dyeing may be performed by a foam-dyeing process, in which a foam containing the modified indigo compound may be contacted with a yarn as the yarn travels through a dyeing chamber. Because of the oxygen stability of embodiments of the modified indigo compounds, the atmosphere in the dyeing chamber may contain oxygen. For instance, in some embodiments, the dyeing chamber may contain air. It is also possible to carefully control the depth of the dye penetration into the yarn using the foam dyeing process. 
     In some embodiments, the substrate such as cotton yarn may be pre-treated with a caustic or cationic agent prior to being contacted with the dye containing the modified indigo compound. The particular caustic or cationic agent may be readily selected by one skilled in the art from such reagents that may be utilized to prepare the substrate for dyeing. Examples of caustic agents that might be used in such a pre-treatment include inorganic alkalis, such as hydroxides such as sodium hydroxide, or potassium hydroxide, carbonates such as sodium carbonate, and the like, and organic alkalis, including members of the amine family such as diethanolamine, trimethylamine, hexamethylenediamine, liquid ammonia, and the like, or combinations thereof. 
     Examples of cationic agents that might be used in such a pretreatment include diallyldimethylammonium chloride (DADMAC), polymerized diallyldimethylammonium chloride (Poly-DADMAC), [2-(acryloyloxy)ethyl] trimethylammonium chloride (AOETMAC), 3-chloro-2-hydroxylpropyl trimethyl-ammonium chloride (CHPTAC, Quat 188), and the like, or combinations thereof. 
     It has been found that such a pre-treatment allows for a consistent and desirable ring dyeing effect. Cotton yarns that are used to prepare denim fabrics are generally “ring dyed”, such that the core of each of the yarns remains undyed, i.e. generally white. In this way, abrasion and/or wear of a denim fabric exposes the core of yarns that make up the fabric in the region of abrasion and/or wear, providing a characteristic fading effect that is desirable in denim garments. In order to avoid dyeing of the core, the concentration of the dye and length of contact time used in the dyeing of cotton yarns must typically be minimized. By pre-treating the cotton yarns as described herein, however, the yarns may be (a) contacted with a dye having a relatively high concentration of modified indigo compound, (b) contacted with the dye for a relatively long period of time, or (c) a combination thereof, without the core of the yarn being dyed. 
     V. KITS CONTAINING THE COMPOUND 
     Also provided are kits comprising one or more dye compound described herein and a reagent or device that converts the compound to indigo. Advantageously, because the above-described compounds are stable in a dried state, they can more easily be transported and/or stored for future use. 
     In some embodiments, the reagent that converts the compound to indigo is a base. In other embodiments, the reagent that converts the compound to indigo is a device that generates heat. In other embodiments, the reagent that converts the compound to indigo is a device that generates steam. 
     It can be seen that the described embodiments provide unique and novel modified indigo compounds and a unique and novel process for dyeing a substrate, such as cotton yarn, using modified indigo compounds, each of which having a number of advantages over those in the art. 
     While there is shown and described herein certain specific structures embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims. 
     The following Examples are provided to illustrate some of the concepts described within this disclosure. While each Example is considered to provide specific individual embodiments of composition, methods of preparation and use, none of the Examples should be considered to limit the more general embodiments described herein. 
     In the following examples, efforts have been made to ensure accuracy with respect to numbers used (e.g. amounts, temperature, etc.) but some experimental error and deviation should be accounted for. Unless indicated otherwise, temperature is in degrees C., pressure is at or near atmospheric. 
     VI. ASPECTS 
     
         
         
           
             1. A method of foam or spray dyeing a substrate, comprising contacting the substrate with a foam or a spray that comprises a dye compound comprising an indigo derivative, or a salt thereof, having one or more modification over the chemical structure of indigo, wherein the indigo derivative has a water-solubility of greater than 0.2% w/v in the absence of a reducing agent and in the presence oxygen, and converts to indigo upon removing the modification, wherein the chemical structure of indigo is the following: 
           
         
       
    
     
       
         
         
             
             
         
       
         
         
           
             2. The method of any one of the preceding Aspects, wherein the foam or spray comprises water. 
             3. The method of Aspect 2, wherein the water is acidic. 
             4. The method of any one of the preceding Aspects, wherein the foam or spray further comprises one or more additional components. 
             5. The method of Aspect 4, wherein said additional component is an acid, cationic agent, caustic agent, chelating agent, color retention agent, coloring agent, dispersant, foaming agent, hydrolyzing agent, mercerization reagent, penetration enhancer, pH buffering agent, salt, solubilizing agent, stabilizing agent, surfactant, thickening agent, tracer, viscosity modifier, or wetting agent. 
             6. The method of any one of the preceding Aspects, wherein the contacting comprises a foam. 
             7. The method of any one of the preceding Aspects, wherein the foam comprises a foaming agent. 
             8. The method of Aspect 7, wherein the foaming agent is a nonionic, anionic, cationic, zwitterionic, or amphoteric surfactant. 
             9. The method of Aspect 8, wherein the foaming agent is present in an amount to provide a stable foam that delivers the dye compound to the substrate and breaks down after application to the substrate. 
             10. The method of any one of the preceding Aspects, wherein the foam comprises a gas. 
             11. The method of any one of the preceding Aspects, wherein the foam comprises about 60 to about 95 wt. %, based on the weight of the foam, of a gas. 
             12. The method of any one of the preceding Aspects, wherein the foam comprises air. 
             13. The method of any one of the preceding Aspects, wherein the foam contains at least about 10% of oxygen. 
             14. The method of any one Aspects 1-5, wherein the contacting comprises a spray. 
             15. The method of Aspect 14, wherein the spray comprises about 60 to about 95 wt. %, based on the weight of the spray, of water. 
             16. The method of any one of the preceding Aspects, wherein the substrate is a natural substrate. 
             17. The method of any one of the preceding Aspects, comprising repeating steps (i) and (ii). 
             18. The method of any one of the preceding Aspects, wherein the spray or foam further comprises a stabilizing agent such as NaCl, Na 2 SO 4 , or combinations thereof. 
             19. The method of any one of the preceding Aspects, wherein the hydrolyzing is performed using a base, heat, steam, or a combination thereof. 
             20. The method of Aspect 19, wherein the base is a hydroxide base, an alkaline earth base, or a carbonate. 
             21. The method of Aspect 19 or 20, wherein the base is a hydroxide base that is sodium hydroxide, potassium hydroxide, or lithium hydroxide. 
             22. The method of Aspect 19, wherein the base is a carbonate that is sodium carbonate or potassium carbonate. 
             23. The method of Aspect 19, wherein heat comprises a temperature of at least about 80° C. such as about 80 to about 200° C., such as about 80 to about 100° C., about 80 to about 120° C., about 80 to about 150° C., or about 80 to about 180° C. 
             24. The method of any one of the preceding Aspects, further comprising: 
             (iii) rinsing the substrate from step (ii). 
             25. The method of Aspect 24, further comprising repeating steps (i) through (iii). 
             26. The method of Aspect 24 or 25, wherein rinsing is performed with an aqueous solution. 
             27. The method of any one of the preceding Aspects, wherein the foam or spray further comprises a neutralization agent or buffering agent. 
             28. The method of any one of the preceding Aspects, wherein the pH of the dyed substrate is adjusted to about 5 to about 9. 
             29. The method of any one of the preceding Aspects, further comprising: 
             (iv) pretreating the substrate prior to step (i). 
             30. The method of Aspect 29, wherein the pretreating is performed with a cationic agent or a caustic agent. 
             31. The method of Aspect 30, wherein the cationic agent is diallyldimethylammonium chloride, polymerized diallyldimethylammonium chloride, [2-(acryloyloxy)ethyl]trimethylammonium chloride, 3-chloro-2-hydroxylpropyl trimethyl-ammonium chloride, or a combination thereof. 
             32. The method of Aspect 30, wherein the caustic agent is sodium hydroxide, potassium hydroxide, sodium carbonate, diethanolamine, trimethylamine, hexamethylenediamine, liquid ammonia, or a combination thereof. 
             33. The method of any one of the preceding Aspects, wherein the substrate is a textile. 
             34. The method of any one of the preceding Aspects, wherein the substrate is a natural substrate such as a plant fiber such as cotton, kapok, hemp, bamboo, flax, sisal, jute, kenaf, ramie, bamboo, soybean, or coconut or an animal substrate such as silk, wool, leather, hair, or feather. 
             35. The method of any one of the preceding Aspects, wherein the substrate is a synthetic substrate such as a polyamide such as nylon, polyester, acrylic, polyolefin, or spandex. 
             36. The method of any one of the preceding Aspects, wherein the substrate is a yarn. 
             37. The method of any one of the preceding Aspects, wherein the substrate is a package of yarn. 
             38. The method of any one of the preceding Aspects, wherein the substrate is a fabric. 
             39. The method of any one of the preceding Aspects, wherein the substrate is dyed denim fabric. 
             40. The method of any one of the preceding Aspects, wherein the spray or foam lacks a reducing agent to convert the compound to a leuco form of the compound. 
             41. The method of Aspect 40, wherein the reducing agent is sodium hydrosulfite, formamidine sulfinic acid, glucose, sodium borohydride, sodium metabisulfite, thiourea dioxide, cellobiose, glyceraldehyde, fructose, or combinations thereof. 
             42. The method of any one of the preceding Aspects, wherein the foam or spray lacks an alkali agent. 
             43. The method of any one of the preceding Aspects, wherein the pH of the foam or spray is less than about 9. 
             44. The method of any one of the preceding Aspects, wherein the foam or spray comprises about 1 wt. % to about 50 wt. %, based on the weight of the foam or spray, of the compound. 
             45. The method of any one of the preceding Aspects, wherein the foam or spray comprises about 2 wt. % to about 30 wt. %, based on the weight of the foam or spray, of the compound. 
             46. The method of any one of the preceding Aspects, wherein less than about 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5 wt. % of the compound in an aqueous solution degrades under atmospheric conditions over a period of about 12 hours in the absence of a reducing agent. 
             47. The method of any one of the preceding Aspects, wherein the dye compound is not: 
             (i) N,N′-dinicotinoyl-[2,2′-biindolinylidene]-3,3′-dione; 
             (ii) the N″,N″′-methylpyridinium bis(methylsulfate) salt of N,N′-dinicotinoyl-[2,2′-biindolinylidene]-3,3′-dione; 
             (iii) N,N′-diacetyl-[2,2′-biindolinylidene]-3,3′-dione; 
             (iv) N,N′-dipropionyl-[2,2′-bi-indolinylidene]-3,3′-dione; 
             (v) N,N′-di-isobutyryl-[2,2′-biindolinylidene]-3,3′-dione; 
             (vi) N,N′-dipivaloyl-[2,2′-biindolinylidene]-3,3′-dione; 
             (vii) N,N′-bis(cyclohexylcarbonyl)-2,2′-bi-indolinylidene-3,3′-dione; 
             (viii) N,N′-bis(3-phenylpropionyl)-2,2′-bi-indolinylidene-3,3′-dione; 
             (ix) N,N′-bis(ethoxycarbonylacetyl)-2,2′-bi-indolinylidene-3,3′-dione; 
             (x) N,N′-bis(2-phenylacetyl)-[2,2′-bi-indolinylidene]-3,3′-dione; 
             (xi) N,N′-bis-(p-methoxyphenylacetyl) 2,2 ′-bi-indolinylidene-3,3′-dione; 
             (xii) N,N′-bis(1-naphthylacetyl)-2,2′-bi-indolinylidene-3,3′-dione; 
             (xiii) N,N′-bis(2-phenylbutyryl)-2,2′-indolinylidene-3,3′-dione; 
             (xiv) (E)-1,1′-di(adamantane-1-carbonyl)-[2,2′-biindolinylidene]-3,3′-dione. 
             (xv) 1H,1′H-[2,2′-biindole]-3,3′-diyl diacetate; 
             (xvi) 3,3′-bis(phenylacetoxy)-2,2′-bi-indolyl; 
             (xvii) 3,3′-bis(p-methoxyphenylacetoxy)-2,2′-bi-indolyl; 
             (xviii) 3,3′-bis(1-napthylacetoxy)-2,2′-bi-indolyl; 
             (xix) 3,3′-bis(phenylbutyryloxy)-2,2′-bi-indolyl; 
             (xx) 3,3′-bis(pivaloyloxy)-2,2′-bi-indolyl; 
             (xxi) 3,3′-bis(1-adamantylcarbonyloxy)-2,2′-bi-indolyl; or 
             (xxii) 3,3′-bis(ethoxycarbonylacetoxy)-2,2′-bi-indolyl. 
             48. The method of any one of the preceding Aspects, wherein the one or more modification enhances the aqueous solubility of the dye compound lacking the modification. 
             49. The method of any one of the preceding Aspects, wherein the one or more modification is a substituent on indigo or the indigo derivative. 
             50. The method of Aspect 49, wherein the substituent is on one or both nitrogen atoms. 
             51. The method of Aspect 49 or 50, wherein the substituent is on one or more carbon atom. 
             52. The method of any one of Aspects 49-51, wherein the substituent is on one more both oxygen atoms. 
             53. The method of any one of Aspects 49-52, wherein the substituent is an alkyl, cycloalkyl, alkoxy, halide, acyl, amine, ester, amide, aryl, heteroaryl, heterocyclyl, sulfonate, carbamate, urea, imine, oxime, anhydride, CN, NO 2 , mesylate, or tosylate, wherein each is optionally substituted. 
             54. The method of any one of the preceding Aspects, wherein the reducing agent is sodium hydrosulfite, formamidine sulfinic acid, glucose, sodium borohydride, sodium metabisulfite, thiourea dioxide, cellobiose, glyceraldehyde, or fructose. 
             55. The method of any one of the preceding Aspects, wherein the compound is of Formula (I) or (II): 
           
         
       
    
     
       
         
         
             
             
         
       
         
         wherein: 
         R 1  and R 2  are, independently, H, SO 3 R C , SO 2 R C , PO 3 (R C ) 2 , C(O)NR A R B , C(O)-(optionally substituted C 1-6 alkyl), C(O)-(optionally substituted aryl), C(O)-(optionally substituted C 1-9 glycolyl), C(O)-(optionally substituted heteroaryl), C(O)-(optionally substituted heterocyclyl), C(O)-(optionally substituted C 1-6 hydroxyalkyl), C(O)O-(optionally substituted C 1-6 alkyl), C(O)O-(optionally substituted aryl), C(O)O-(optionally substituted C 1-9 glycolyl), C(O)O-(optionally substituted C 1-6 hydroxyalkyl), C(O)O-(optionally substituted heteroaryl), C(O)O-(optionally substituted heterocyclyl); or 
         R 3  and R 4  are, independently, H, halide, optionally substituted C 1-6 alkyl, optionally substituted C 1-6 hydroxyalkyl, optionally substituted C 1-6 alkoxy, optionally substituted aryl, or SO 3 H; 
         R 7  and R 8  are, independently, H, SO 3 R C , SO 2 R C , PO 3 (R C ) 2 , C(O)NR A R B , C(O)-(optionally substituted C 1-6 alkyl), C(O)-(optionally substituted aryl), C(O)-(optionally substituted C 1-9 glycolyl), C(O)-(optionally substituted C 1-6 hydroxyalkyl), C(O)-(optionally substituted heteroaryl), C(O)-(optionally substituted heterocyclyl), C(O)O-(optionally substituted C 1-6 alkyl), C(O)O-(optionally substituted aryl), C(O)O-(optionally substituted C 1-9 glycolyl), C(O)O-(optionally substituted C 1-6 hydroxyalkyl), C(O)O-(optionally substituted heteroaryl), or C(O)O-(optionally substituted heterocyclyl); 
         R A  and R B  are, independently, H or optionally substituted C 1-6 alkyl, or optionally substituted aryl; 
         R C  is H, optionally substituted C 1-6 alkyl, optionally substituted C 3-8 cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl; 
         m and n are, independently, 0 to 4; 
         or a salt thereof. 
         56. The method of Aspect 55, wherein when the compound is of Formula (I), R 3  and R 4  are not H, when R 1  and R 2  are both 1-methyl-pyridyl-3-yl. 
         57. The method of Aspect 55 or 56, wherein m is 0. 
         58. The method of any one of Aspects 55-57, wherein n is 0. 
         59. The method of Aspect 55 or 56, wherein R 3  is a halide. 
         60. The method of any one of Aspects 55, 56, or 59, wherein R 4  is a halide. 
         61. The method of any one of Aspects 55, 56, or 60, wherein R 3  is C 1-6 alkyl. 
         62. The method of any one of Aspects 55, 56, 59, or 61, wherein R 4  is C 1-6 alkyl. 
         63. The method of any one of Aspects 55-62, wherein one of R 1  or R 2  is H. 
         64. The method of any one of Aspects 55-63, wherein one of R 1  and R 2  is SO 3 H. 
         65. The method of any one of Aspects 55-64, wherein the compound is of Formula (I): 
       
    
     
       
         
         
             
             
         
       
         
         66. The method of any one of Aspects 55-65, wherein one or both of R 1  and R 2  is C(O)-(optionally substituted heteroaryl). 
         67. The method of any one of Aspects 55-66, wherein one or both of R 1  and R 2  is C(O)-(optionally substituted pyridyl), such as C(O)-(optionally substituted 2-pyridyl), C(O)-(optionally substituted 3-pyridyl), or C(O)-(optionally substituted 4-pyridyl). 
         68. The method of Aspect 67, wherein the pyridyl is substituted with C 1-6 alkyl. 
         69. The method of Aspect 67 or 68, wherein the pyridyl is substituted with one or more methyl or ethyl. 
         70. The method of any one of Aspects 67-69, wherein the pyridyl is substituted on the N-atom. 
         71. The method of any one of Aspects 55-65, wherein one or both of R 1  and R 2  is C(O)-(optionally substituted aryl), such as C(O)-(optionally substituted phenyl). 
         72. The method of any one of Aspects 55-65, wherein one or both of R 1  and R 2  is C(O)NR A R B , wherein one or both of R A  and R B  is H, optionally substituted C 1-6 hydroxyalkyl, or optionally substituted C 1-6 alkyl. 
         73. The method of any one of Aspects 55-65, wherein one or both of R 1  and R 2  are C(O)O-(optionally substituted heterocyclyl) such as C(O)O-(optionally substituted pyrrolidone). 
         74. The method of any one of Aspects 55-65, wherein one or both of R 1  and R 2  are, independently, C(O)O-(optionally substituted alkyl) such as C(O)O(alkyl substituted with heterocyclyl) such as C(O)O(alkyl substituted with glucosyl). 
         75. The method of any one of Aspects 55-65, wherein one or both of R 1  and R 2  are, independently, C(O)(optionally substituted C 1-6 hydroxyalkyl). 
         76. The method of any one of Aspects 55-65, wherein one or both of R 1  and R 2  are, independently, C(O)O(optionally substituted C 1-6 hydroxyalkyl). 
         77. The method of any one of Aspects 55-65, wherein one or both of R 1  and R 2  are, independently, C(O)(optionally substituted C 1-9 glycol). 
         78. The method of any one of Aspects 55-64, which is of Formula (II): 
       
    
     
       
         
         
             
             
         
       
         
         79. The method of Aspect 78, wherein one or both of R 1  and R 2  are H. 
         80. The method of Aspect 78 or 79, wherein one or both of R 7  and R 8  are H. 
         81. The method of Aspect 78 or 79, wherein one of R 7  and R 8  are SO 3 H. 
         82. The method of Aspect 78 or 79, wherein one or both of R 7  and R 8  are C(O)(optionally substituted heteroaryl) such as C(O)(optionally substituted pyridyl). 
         83. The method of Aspect 78 or 79, wherein one or both of R 7  and R 8  are C(O)(optionally substituted C 1-6 alkyl). 
         84. The method of Aspect 83, wherein the C 1-6 alkyl is substituted with C(O)O(C 1-6 alkyl) such as C(O)OCH 2 CH 3 . 
         85. The method of Aspect 78 or 79, wherein one or both of R 7  and R 8  are C(O)-(optionally substituted aryl) such as C(O)-(optionally substituted phenyl). 
         86. The method of Aspect 85, wherein the phenyl is substituted with CO 2 H. 
         87. The method of any one of the preceding Aspects, wherein the compound is an acid or base addition salt. 
         88. The method of any one of the preceding Aspects, wherein the compound is a sulfate salt, alkylsulfate salt, bisulfate salt, phosphate salt, or halide salt. 
         89. The method of Aspect 88, wherein the halide salt is an iodide salt, chloride salt, bromide salt, or fluoride salt. 
         90. The method of Aspect 88, wherein the compound is an alkylsulfate salt. 
         91. The method of Aspect 90, wherein the compound is a methylsulfate or ethylsulfate salt. 
         92. The method of any one of Aspects 1-54, wherein the compound is of Formula (IA): 
       
    
     
       
         
         
             
             
         
       
         
         wherein: 
         R 5  and R 6  are, independently, H or C 1-6 alkyl; and 
         X is halide, sulfate, C 1-6 alkylsulfate, bisulfate, or phosphate; 
         with the proviso that both R 5  and R 6  are not CH 3  when X is CH 3 SO 4   − . 
         93. The method of any one of Aspects 1-54, wherein the compound is of Formula (IB) or (IC): 
       
    
     
       
         
         
             
             
         
       
         
         wherein:
       R 5  and R 6  are, independently, H or C 1-6 alkyl; and   X is halide, sulfate, C 1-6 alkylsulfate, bisulfate, or phosphate.   
     
         94. The method of any one of Aspects 1-54, wherein the compound is: 
       
    
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
         
         wherein X is a counteranion. 
         95. The method of any one of Aspects 1-54, wherein the compound is 
       
    
     
       
         
         
             
             
         
       
         
         wherein X is acetate, propionate, lactate, citrate, tartrate, succinate, fumarate, maleate, malonate, mandelate, phthalate, Cl, Br, I, F, phosphate, nitrate, sulfate, ethanesulfonate, phosphonate, napthalenesulfonate, benzenesulfonate, toluenesulfonate, camphorsulfonate, methanesulfate, ethanesulfonate, napthalenesulfate, benzenesulfate, toluenesulfate, camphorsulfate, bisulfate, sulfite, or bisulfite. 
         96. The method of any one of Aspects 1-54, wherein the compound is: 
       
    
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
         
         wherein, X is a counteranion. 
         97. The method of any one of Aspects 1-54, wherein the compound is: 
       
    
     
       
         
         
             
             
         
       
     
     or a salt thereof.
     98. The method of any one of Aspects 1-54, wherein the compound is:   

     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     or a salt thereof.
     99. The method of any one of Aspects 1-54, wherein the compound is:   

     
       
         
         
             
             
         
       
     
     or salt thereof.
     100. The method of any one of Aspects 1-54, wherein the compound is:   

     
       
         
         
             
             
         
       
     
     or a salt thereof
     101. The method of any one of Aspects 1-54, wherein the compound is:   

     
       
         
         
             
             
         
       
     
     or a salt thereof.
     102. The method of any one of Aspects 1-54, wherein the compound is:   

     
       
         
         
             
             
         
       
         
         103. The method of any one of Aspects 1-54, wherein the compound is: 
       
    
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     or a salt thereof.
     104. The method of any one of the preceding Aspects, wherein the compound converts to indigo through hydrolysis, such as using a hydrolyzing agent, heat, steam, or combinations thereof.   105. The method of any one of the preceding Aspects, wherein the compound is substantially stable in the presence of oxygen such as in aqueous solutions.   106. The method of any one of the preceding Aspects, wherein the compound has greater water solubility than indigo.   107. The method of any one of the preceding Aspects, which is resist dyeing.   108. A dyed substrate prepared according to the methods of any one of the preceding Aspects.   109. A spray for dyeing a substrate, the spray comprising water and a dye compound comprising an indigo derivative, or a salt thereof, having one or more modification over the chemical structure of indigo, wherein the indigo derivative has a water-solubility of greater than 0.2% w/v in the absence of a reducing agent and in the presence oxygen, and converts to indigo upon removing the modification.   110. A foam for dyeing a substrate, comprising air and a dye compound comprising an indigo derivative, or a salt thereof, having one or more modification over the chemical structure of indigo, wherein the indigo derivative has a water-solubility of greater than 0.2% w/v in the absence of a reducing agent and in the presence oxygen, and converts to indigo upon removing the modification;   wherein the foam comprises at least about 10 wt. %, based on the total weight of the foam, of oxygen.   

     VII. EXAMPLES 
     All UV-Vis spectra were obtained using a Varian Cary 6000i UV-Vis spectrophotometer. 
     Reactions of indigo with nicotinoyl chloride/isonicotinoyl chloride 
     Example 1: Synthesis of Compounds 2 and 6 
     
       
         
         
             
             
         
       
     
     To a suspension of indigo (54 g, 0.206 mol) in anhydrous pyridine (200 mL) in a LOL flask fitted with a condenser and mechanical stirrer, under an inert atmosphere (Ar or N 2 ) was added isonicotinoyl chloride (92 g, 0.515 mol, 2.5 equivalents) portion wise with efficient stirring. The reaction mixture was heated to 50° C. for 6 hours (the progress of the reaction was followed by TLC (5% MeOH in DCM, Rf 0.5). After this time, the deep red/pink reaction mixture was allowed to cool and most of the pyridine was removed under vacuum. The resulting reaction mixture was quenched by pouring into cold water (500 mL) with stirring for 30 minutes. The solid precipitate thus formed was isolated by filtration and washed thoroughly with cold water. The deep red solid was dried under vacuum and then dissolved in dichloromethane (1 L); this solution was further dried using anhydrous sodium sulfate. The deep red solution was filtered and concentrated under vacuum until dry to afford a deep purple/red solid (60 g, 61.8% yield). Characterization by  1 HNMR and MS confirmed the desired compounds. 
     Compound 2: Mw=C 28 H 16 N 4 O 4 , 472.45;  1 H NMR (400 MHz, DMSO) δ 9.02 (s, 2H), 8.81-8.75 (m, 2H), 8.62-8.61 (m, 2H), 7.71 (d, J=7.4 Hz, 1H), 7.69-7.63 (m, 1H), 7.61 (dd, J=7.8, 4.9 Hz, 4H), 7.48 (dd, J=9.3, 5.8 Hz, 2H), 7.28 (t, J=7.8 Hz, 2H), 7.28 (t, J=7.8 Hz, 2H). 
     Compound 6: Mw=C 28 H 16 N 4 O 4 , 472.45;  1 H NMR (400 MHz, DMSO) δ 8.82 (d, J=5.7 Hz, 4H), 7.80 (d, J=18.1 Hz, 4H), 7.70 (d, J=7.5 Hz, 2H), 7.65 (t, J=7.6 Hz, 2H), 7.60-7.35 (m, 2H), 7.28 (t, J=7.6 Hz, 2H). 
     Example 2: Synthesis of Compound 28 
     
       
         
         
             
             
         
       
     
     To a suspension of indigo (5.2 g, 20 mmol) in anhydrous pyridine (50 mL) in a flask fitted with a condenser and mechanical stirrer, under an inert atmosphere (Ar or N2) was added 2-nicotinoyl chloride (14.2 g, 80 mmol, 4 equiv) portion wise with efficient stirring. The brown reaction mixture became quite thick and warm and was allowed to stir at room temperature for 30 mins and then gradually heated to 50° C. hours (the progress of the reaction was followed by TLC (5% MeOH in DCM, Rf 0.3). The resulting reaction mixture was quenched by pouring into cold water (200 mL) with stirring for 30 minutes. The solid precipitate isolated by filtration proved to be un-reacted indigo. The aqueous was extracted into dichloromethane (3×50 mL), dried and concentrated to a give a brown solid which was purified using flash column chromatography. The main product isolated (stained yellow on TLC, Rf=0.3 as above) as a yellow solid and was characterised by NMR. The analysis was not consistent with the above structure indicating that the 2-derivative behaves quite differently from the 3 and 4-derivatives when reacted with indigo. 
       1 H NMR (400 MHz, DMSO) δ 8.82 (d, J=4.7 Hz, 1H), 8.71 (d, J=4.1 Hz, 1H), 8.31 (t, J=7.7 Hz, 1H), 8.09-7.95 (m, 1H), 7.88-7.79 (m, 1H), 7.68-7.59 (m, 1H), 7.47-7.39 (m, 1H), 7.36 (dd, J=6.5, 1.7 Hz, 1H), 6.32 (d, J=9.2 Hz, 1H), 6.19-6.14 (m, 1H). 
     Example 3: Synthesis of Compound 15 
     
       
         
         
             
             
         
       
     
     To a suspension of indigo (20 g, 0.076 mol) in anhydrous pyridine (100 mL) in a flask fitted with a condenser and mechanical stirrer, under an inert atmosphere (Ar or N2) was added isonicotinoyl chloride (13 g, 0.076 mol, 1 equiv) portion wise with efficient stirring. The reaction mixture was heated to 50° C. for 6 hours (the progress of the reaction was followed by TLC (5% MeOH in DCM, Rf 0.6; TLC also showed the presence of some di-substituted product). After this time, the deep red/pink reaction mixture was allowed to cool and most of the pyridine was removed under vacuum. The resulting reaction mixture was quenched by pouring into cold water (500 ml) with stirring for 30 minutes. The solid precipitate thus formed was isolated by filtration and washed thoroughly with cold water. The deep red solid was dried under vacuum and then dissolved in dichloromethane (1 L); this solution was further dried using anhydrous sodium sulphate. The deep red solution was filtered and concentrated under vacuum until dry to afford a deep purple/red solid. The crude material was separated by flash column chromatography (1% MeOH/dichloromethane). The pure product was separated as a bright pink solid in 25% yield (7 g). 
     Mw, C 22 H 13 N 3 O 3 , 367.36;  1 H NMR (400 MHz, DMSO) δ 11.05 (s, 1H), 8.67 (d, J=5.9 Hz, 2H), 7.88 (d, J=7.5 Hz, 1H), 7.80-7.68 (m, 4H), 7.52 (t, J=7.7 Hz, 1H), 7.39 (dd, J=12.4, 7.2 Hz, 2H), 7.29 (d, J=8.1 Hz, 1H), 6.92 (t, J=7.4 Hz, 1H). 
     Quaternization of nicotinoyl/isonicotinoyl derivatives 
     Example 4: Synthesis of Compounds 3 and 7 
     
       
         
         
             
             
         
       
     
     To a refluxing solution of the precursor (Compound 2 or 6) in acetone, methyl iodide (3.2 equiv) was added drop-wise over 20 mins. The mixture was allowed to reflux for a further 5 hours and then allowed to cool to 0° C.; the precipitated product was isolated by filtration and washed with ethyl acetate:pet ether (1:1) and dried. The brown solid was isolated in quantitative yield. 
     Compound 3: Mw, 756.33, C 30 H 22 I 2 N 4 O 4    
     Compound 7: Mw, 756.33, C 30 H 22 I 2 N 4 O 4 ;  1 H NMR (400 MHz, DMSO) δ 9.28 (d, J=6.5 Hz, 4H), 8.50-8.38 (m, 4H), 8.14 (d, J=8.2 Hz, 2H), 7.85-7.76 (m, 4H), 7.41 (t, J=7.5 Hz, 2H). 4.64 (s, 6H). 
     Example 5: Synthesis of Compound 16 
     
       
         
         
             
             
         
       
     
     To a refluxing solution of the precursor in acetone, methyl iodide (1.25 equiv) was added drop-wise over 20 mins. The mixture was allowed to reflux for a further 18 hours and then allowed to cool to 0° C.; the precipitated product was isolated by filtration and washed with ethyl acetate:pet ether (1:1) and dried. 
     Mw, 614.14, C 29 H19IN 4 O 4    
     Example 6: Synthesis of Compound 18 
     
       
         
         
             
             
         
       
     
     Compound 6 (0.05 mol) was introduced into a pressure flask to which was added acetone (250 mL). The solution was saturated with chloromethane gas and sealed. The flask was heated to 100° C. for 48 hours with stirring. After this time, the flask was allowed to cool to room temperature (TLC indicated complete consumption of the starting material). The product, which precipitated out, was isolated by filtration and washed with acetone and dried to constant weight. After drying, a purple solid was isolated which was characterized by  1 H NMR (59% yield). 
     Mw 573.0, C 30 H 22 N 4 O 4 C 2 ;  1 H NMR (DMSO): δ 9.2 (d, 4H, J=6.5 Hz), 8.5 (d, 4H, J=6.5 Hz), 8.1 (d, 2H, J=8.2 Hz), 67.8 (m, 4H) 7.4 (d, 2H, J=11 Hz), 4.4 (6H s). 
     Example 7: Synthesis of Compound 3B 
     
       
         
         
             
             
         
       
     
     Compound 2 (0.05 mol) is introduced into a pressure flask to which is added acetone (250 mL). The solution is saturated with chloromethane gas and sealed. The flask is heated to 100° C. for 48 hours with stirring. After this time, the flask is allowed to cool to room temperature. The product, which precipitates out, is isolated by filtration and washed with acetone and dried to constant weight. After drying, a purple solid is isolated. 
     Example 8: Synthesis of Compounds 4, 8 and 41 
     
       
         
         
             
             
         
       
     
     Compound 2 or 6 was heated with anhydrous dialkylsulfate (R 2 SO 4 , R=Me, Et; 5 equiv) with stirring at 50° C. for 18 hours under an inert atmosphere. TLC after this time showed the complete consumption of starting material. Once the reaction mixture was allowed to cool to room temperature, anhydrous diethyl ether (20 equiv) was added and the mixture stirred for 30 minutes. After this time, stirring was stopped and the precipitated compound was allowed to settle. The supernatant was removed via a filtered cannula under argon pressure. This process was repeated twice more to ensure removal of residual dimethyl sulfate. The solid residue was dried under a stream of Ar and stored under Ar, giving the product in almost quantitative yield 
     Compound 4 (J. Chem. Perk. Trans. 1984 2305-2309); Mw, 724.11, C 32 H28N4012S2;  1 H NMR (400 MHz, CDCl 3 ) δ 9.56 (s, 2H), 9.11 (d, 4H), 8.43 (dd, 2H), 8.0-7.4 (m, 8H). 4.51 (s, 6H). 
     Compound 8: Mw, 724.11, C 32 H 28 N 4 O 12 S 2 ;  1 H NMR (DMSO): δ 9.2 (d, 4H, J=6.6 Hz), 8.4 (d, 4H, J=6.6 Hz), 8.1 (d, 2H, J=7.4 Hz), 7.8 (t, 4H, J=8.1 Hz), 7.4 (d, 2H, J=7.4 Hz), 4.5 (s, 6H). 
     Compound 41: Mw, 724.11, C 32 H 28 N 4 O 12 S 2 ; H NMR (400 MHz, DMSO) δ 9.35 (d, J=10.0 Hz, 4H), 8.54-8.38 (m, 4H), 8.14 (d, J=8.3 Hz, 2H), 7.78 (m, 6H), 7.48-7.34 (t, J=12.1 Hz, 2H), 4.34 (q, J=7.1 Hz, 4H), 3.74 (q, J=7.1 Hz, 4H), 1.34 (t, J=7.1 Hz, 6H), 1.1 (t, J=7.1 Hz, 6H). 
     Example 9: Synthesis of Compound 17 
     
       
         
         
             
             
         
       
     
     Compound 15 was heated with anhydrous dimethyl sulfate (5 equiv) with stirring at 50° C. for 18 hours under an inert atmosphere. TLC after this time showed the complete consumption of starting material. Once the reaction mixture was allowed to cool to room temperature, anhydrous diethyl ether (20 equiv) was added and the mixture stirred for 30 minutes. After this time, stirring was stopped and the precipitated compound was allowed to settle. The supernatant was removed via a filtered cannula under argon pressure. This process was repeated twice more to ensure removal of residual dimethyl sulfate. The solid residue was dried under a stream of Ar and stored under Ar, giving the product in almost quantitative yield 
     Mw C 24 H 19 N 3 O 7 S, 493.43;  1 H NMR (400 MHz, DMSO) δ 11.08 (s, 1H), 9.01 (d, J=6.5 Hz, 2H), 8.51 (d, J=6.5 Hz, 2H), 8.03 (d, J=8.3 Hz, 1H), 7.93 (d, J=7.5 Hz, 1H), 7.78 (t, J=7.8 Hz, 1H), 7.53 (t, J=7.5 Hz, 1H), 7.46 (d, J=7.4 Hz, 1H), 7.41 (d, J=7.5 Hz, 1H), 7.30 (d, J=8.1 Hz, 1H), 6.94 (t, J=7.4 Hz, 1H), 4.29 (s, 3H), 3.95 (s, 3H). 
     Protonation of nicotinoyl/isonicotinoyl derivatives 
     Example 10: Synthesis of Compound 35 
     
       
         
         
             
             
         
       
     
     Compound 6 (0.060 mol; as prepared above) was introduced into a flask to which was added dichloromethane (1 L). A stream of hydrogen chloride gas was passed through the solution so formed at room temperature with occasional stirring. After a few minutes, the reaction mixture thickened and a precipitate formed. The mixture was allowed to stand under an atmosphere of HCl gas for 1 hour. The solvent was removed under vacuum and the product was co-evaporated with anhydrous DCM (2×50 mL) and dried to constant weight to afford a purple solid, compound 35 (quantitative yield). 
     Mw, C 28 H 18 N 4 O 12 C 2 , 545;  1 H NMR (400 MHz, DMSO) δ 9.22 (bs, 4H), 8.28 (d, J=5.3 Hz, 4H), 8.08 (bs, 2H), 7.82-7.68 (m, 4H), 7.35 (t, J=12.7 Hz, 2H). 
     Example 11: Synthesis of Compound 44 
     
       
         
         
             
             
         
       
     
     Compound 2 (0.060 mol; as prepared above) is introduced into a flask to which is added dichloromethane (1 L). A stream of hydrogen chloride gas is passed through the solution at room temperature with occasional stirring. After a few minutes, the reaction mixture thickens and a precipitate forms. The mixture is allowed to stand under an atmosphere of HCl gas for 1 hour. The solvent is removed under vacuum and the product is co-evaporated with anhydrous DCM (2×50 mL) and dries to constant weight. 
     Example 12: Synthesis of Compound 37 
     
       
         
         
             
             
         
       
     
     To a solution of compound 6 (5.0 g, 10.6 mmol) in dichloromethane (30 mL) at 0° C. under an atmosphere of argon was added a solution of anhydrous sulphuric acid (0.021 mol, 2.1 g) in methanol (25 mL) drop-wise with stirring over 30 mins. The mixture was allowed to stir at 0° C. for a further 30 mins and then allowed to warm to room temperature. After 1 hour, anhydrous diethyl ether (100 mL) was added and the mixture stirred for 10 mins and then stirring was stopped and the precipitated solid was allowed to settle. The supernatant was removed by a filtered cannula under argon pressure; this process was repeated twice using 50 mL of diethyl ether each time. The product was isolated in quantitative yield as a bright red solid (7.0 g). 
     Mw C 28 H 20 N 4 O 12 S 2 , 668.47; mass analysis was consistent with the formation of the corresponding ion. 
     Compound 37 hydrolyzes to indigo under hydrolyzing conditions. 
     Reactions of indigo with alkoxy ethers 
     Example 13: Synthesis of Compound 13 
     
       
         
         
             
             
         
       
     
     Triphosgene (23.8 g, 80 mmol) was added to pyridine at 0° C. and the mixture then allowed to warm to room temperature. After stirring for 30 mins at room temperature, indigo (10.5 g, 40 mmol) was added in one portion and the reaction allowed to stir overnight at room temperature. The mixture was then cooled in an ice bath and poured into ice cooled 4M HCl aq  with vigorous stirring and the precipitated solid was isolated by filtration. The solid was further washed with cold 4M HCl aq  followed by H 2 O. The solid was then dried under vacuum at 40° C. to give a grey solid. This crude material was used for the following reactions. 
     Example 14: Synthesis of Compounds 14, 25, 29, 30, and 33 
     
       
         
         
             
             
         
       
     
     Compound 13 (3.0 g, 7.7 mmol) as prepared above) was suspended in the appropriate solvent (30 mL) and cooled in an ice-bath under an inert atmosphere. To this was added a THE solution of the alkoxy compound drop-wise (noted as “R” in Table 1) with stirring over 15 mins. The reaction mixture was allowed to stir at 0° C. for 1 hour and then allowed to warm to room temperature over 18 hours (the progress of the reaction was followed by TLC 5% MeOH/DCM). The solvents were removed under vacuum followed by addition of diethyl ether (200 ml) and stirred for 30 mins before decanting. The brown residue was taken up in DCM and purified using flash column chromatography. Fractions were characterized by  1 H NMR. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Compound 
                 R 
                 Solvent 
               
               
                   
               
             
            
               
                 14 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 Pyridine:THF (1:1) 
               
               
                   
               
               
                 25 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 Pyridine:THF (1:1) 
               
               
                   
               
               
                 29 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 Pyridine, 2 equiv Et 3 N 
               
               
                   
               
               
                 30 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 Pyridine, 2 equiv Et 3 N 
               
               
                   
               
               
                 31 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 THF 
               
               
                   
               
               
                 33 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 THF 
               
               
                   
               
            
           
         
       
     
     Reactions of Leuco-Indigo 
     These reactions were carried out by generating leuco-indigo in-situ by oxidation of indigo by zinc and sodium acetate in the presence of acid chloride. 
     Example 15: Synthesis of Compound 24B 
     
       
         
         
             
             
         
       
     
     To a suspension of indigo (1.31 g, 5 mmol) in anhydrous ethyl acetate (50 mL) containing sodium acetate (1.03 g, 12.5 mmol) and zinc (3.25 g, 50 mmol) was added ethyl malonyl chloride (8.3 g, 50 mmol). The reaction mixture was allowed to stir for 30 mins at 40° C. The suspension was allowed to cool to room temperature and then concentrated to dryness. The residue was extracted with hot acetone. The crude material was purified using flash column chromatography eluting with 20% ethyl acetate:pet ether. The product was isolated as a pale yellow solid (0.5 g, 26%). 
     Mw=C 21 H 18 N 2 O 5 , 378.38;  1 H NMR (400 MHz, DMSO) δ 12.17 (s, 1H), 11.90 (s, 1H), 8.27 (d, 7.5 Hz, 1H), 7.57-7.45 (m, 3H), 7.32-7.20 (m, 3H), 7.15 (ddd, J=8.0, 7.0, 1.0 Hz, 1H), 4.05 (q, J=7.1 Hz, 2H), 3.82 (s, 2H), 1.12-1.05 (t, 7.1 Hz, 3H). 
     Example 16: Synthesis of Compound 22 
     
       
         
         
             
             
         
       
     
     To a suspension of indigo (1.0 g, 3.8 mmol) in anhydrous ethyl acetate (50 ml) containing sodium acetate (0.8 g, 9.5 mmol) and zinc (2.49 g, 38 mmol) was added isonicotinoyl chloride (2.0 g, 11.4 mmol). The reaction mixture was allowed to stir for 30 mins at 40° C. The suspension was allowed to cool to room temperature and then concentrated to dryness. The residue was extracted with hot acetone. The crude material was purified using flash column chromatography eluting with 20% ethyl acetate:pet ether. The product was isolated as a pale yellow solid and was confirmed by  1 H NMR to be the di-substituted product, Compound 22 (0.4 g, 22%). 
     Mw, C 28 H 18 N 4 O 4 , 474.47; H NMR (400 MHz, DMSO) δ 11.36 (s, 1H), 11.12 (s, 1H), 7.59 (d, J=8.0 Hz, 1H), 7.50 (dd, J=8.1, 0.9 Hz, 1H), 7.46-7.41 (d, 8.1 Hz, 1H), 7.36 (d, J=8.1 Hz, 1H), 7.16 (dddd, J=12.9, 8.2, 7.0, 1.2 Hz, 2H), 7.05 (ddt, J=8.1, 7.0, 1.1 Hz, 2H), 6.84 (dd, J=2.1, 0.8 Hz, 1H). 
     Example 17: Synthesis of Compound 20 
     
       
         
         
             
             
         
       
     
     Indigo (0.824 g, 3.1 mmol) was dissolved in pyridine and to this was added 3-benzoyl chloride sulfonyl chloride (3 g, 12.4 mmol). The mixture was heated to 50° C. for 18 hours. After this time, the deep red mixture was poured onto cold water (100 ml) and stirred for 30 mins. The solid was isolated by filtration, dried under vacuum (1.98 g, 69% yield) and characterised. 
     Example 18: Synthesis of Compound 27 
     
       
         
         
             
             
         
       
     
     Indigo (5.2 g, 20 mmol) was dissolved in pyridine and to this was added 3-sulphoyll chloride benzoic acid (17.4 g, 80 mmol). The mixture was heated to 50° C. for 18 hours. After this time, the deep red mixture was poured onto cold water (100 ml) and stirred for 30 mins. The mixture was concentrated under vacuum to remove pyridine and the crude material was purified by column chromatography. The main fraction isolated by characterised by  1 H NMR. 
     Example 19: Synthesis of Compound 11 
     
       
         
         
             
             
         
       
     
     Indigo (2.62 g, 10 mmol) was added portion-wise to a suspension of N,N′-Disuccinimidyl carbonate (7.68 g, 30 mmol) in THE containing pyridine (0.125 mL) at 45° C. with rapid stirring. The reaction mixture was allowed to stir at this temperature for 48 hours (the progress of the reaction was monitored by TLC, 5% MeOH/DCM). After this time, TLC showed a considerable amount of un-reacted indigo was still present; this was removed by filtration and the solid washed with DCM. The organic filtrate was concentrated to dryness and re-dissolved in DCM, washed with NaHCO 3  followed by H 2 O and then dried. Concentration under vacuum afforded a dark brown oil which was purified by column chromatography. 
     Example 20: Synthesis of Compound 23 
     
       
         
         
             
             
         
       
     
     To a suspension of indigo (1.0 g, 3.8 mmol) in anhydrous ethyl acetate (50 mL) containing sodium acetate (0.8 g, 9.5 mmol) and zinc (2.49 g, 38 mmol) was added chlorosulfonic acid (2.2 g, 19 mmol). The reaction mixture was allowed to stir for 30 mins at 40° C. The suspension was allowed to cool to room temperature and then filtered to remove zinc. The yellow brown filtrate was concentrated to dryness to give dark yellow oil. 
     Example 21: Synthesis of Compound 24A 
     
       
         
         
             
             
         
       
     
     To a suspension of indigo (1.31 g, 5 mmol) in anhydrous ethyl acetate (50 mL) containing sodium acetate (1.03 g, 12.5 mmol) and zinc (3.25 g, 50 mmol) is added ethyl malonyl chloride (8.3 g, 50 mmol). The reaction mixture is allowed to stir at 40° C. for at least 1 hour. The suspension is allowed to cool to room temperature and then concentrates to dryness. The residue is extracted with hot acetone. The crude material is purified using flash column chromatography eluting with 20% ethyl acetate:pet ether. 
     Example 22: Synthesis of Compound 38 
     
       
         
         
             
             
         
       
     
     This compound is prepared using the procedure for Compound 18 in Example 6 using the corresponding free base. 
     Example 23: Synthesis of Compound 39 
     
       
         
         
             
             
         
       
     
     This compound is prepared using the procedure for Compound 37 in Example 12 using the corresponding free base. 
     Example 24: Synthesis of Compound 43 
     
       
         
         
             
             
         
       
     
     This compound is prepared by dissolving Compound 6 in DCM, followed by addition of chloroethane gas in dichloromethane/ethanol, dichloromethane/Bu 4 N + Br − , ethanol, ethanol/pyridine, or isopropanol in a sealed pressure tube at 100° C. The compound was then purified and isolated. 
     Example 25 
     White 100% polyester pants were sprayed using a 6% Compound 8 aqueous solution containing 5% thickener. The formulation contain 6% (w/v) compound 8, 2% Ecosurf EH-9 surfactant, and 5% polyacrylic acid. Sprayer: 3-30 psi was used, Central Pneumatic Air Sprayer, 20 oz high volume, low pressure, gravity feed spray gun, ½″-18 NPS Air inlet. Hydrolyzed in 1 M NaOH by dip for 4 minutes, then rinse. Air dried. Template that was used for pattern:acetate. 
       FIG. 1  demonstrates successful patterning on polyester using modified indigo by spray. 
     Example 26 
     A white 100% cotton jacket was sprayed using a 6% Compound 8 aqueous solution containing 5% thickener. A resist was used to maintain the pattern and mask deposition of Compound 8. Formulation: 6% (w/v) compound 8, 2% Ecosurf EH-9 surfactant, 5% hydroxypropylcellulose. Sprayer: 3-30 psi was used, Central Pneumatic Air Sprayer, 20 oz high volume, low pressure, gravity feed spray gun, ¼″-18 NPS Air inlet. Hydrolyzed in 1 M NaOH by dip for 4 minutes, then rinse. Air dried.  FIG. 2  demonstrates successful patterning using modified indigo by spray using a resist. 
     Example 27 
     Denim pants were sprayed using a 6% Compound 8 aqueous solution containing 5% thickener. Formulation: 6% (w/v) compound 8, 2% Ecosurf EH-9 surfactant, 5% hydroxypropylcellulose. Sprayer: 3-30 psi was used, Central Pneumatic Air Sprayer, 20 oz high volume, low pressure, gravity feed spray gun, ¼″-18 NPS Air inlet. Hydrolyzed in 1 M NaOH by dip for 4 minutes, then rinse. Air dried.  FIG. 3  demonstrates successful patterning on denim using modified indigo by spray. 
     Example 28 
     A denim jacket was sprayed using a 6% Compound 8 aqueous solution containing 5% thickener. Formulation: 6% (w/v) compound 8, 2% Ecosurf EH-9 surfactant, 5% hydroxypropylcellulose. Sprayer: 3-30 psi was used, Central Pneumatic Air Sprayer, 20 oz high volume, low pressure, gravity feed spray gun, ¼″-18 NPS Air inlet. Hydrolyzed in 1 M NaOH by dip for 4 minutes, then rinse. Air dried. Template that was used for pattern:acetate.  FIG. 4  demonstrates successful patterning on denim using modified indigo by spray using a template. 
     Example 29 
     A sheet of yarn is contacted with a foam generated using a 6% Compound 8 aqueous solution containing 0.1% Steol CS270 and 0.5% Alfol 810. 
     Example 30 
     A sheet of yarn is yarn is sprayed with a foam generated using a 10% Compound 8 aqueous solution containing 1% Tergitol NP-9. 
     It is to be understood that while the invention has been described in conjunction with the preferred specific embodiments thereof, that the foregoing description and the examples that follow are intended to illustrate and not limit the scope of the invention. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention, and further that other aspects, advantages and modifications will be apparent to those skilled in the art to which the invention pertains. In addition to the embodiments described herein, the present invention contemplates and claims those inventions resulting from the combination of features of the invention cited herein and those of the cited prior art references which complement the features of the present invention. Similarly, it will be appreciated that any described material, feature, or article may be used in combination with any other material, feature, or article, and such combinations are considered within the scope of this invention. 
     The disclosures of each patent, patent application, and publication cited or described in this document are hereby incorporated herein by reference, each in its entirety, for all purposes.