Sensitizing dye for photographic materials

Abstract: Sensitizing dyes for photographic materials are disclosed. The dyes have the formula: wherein Z₁ represents the atoms necessary to complete a benzoxazole nucleus, a benzothiazole nucleus, a benzoselenazole nucleus, a benzotellurazole nucleus, or a benzimidazole nucleus, which, in addition to being substituted by R₃, may be further substituted or unsubstituted, Z₂ represents the atoms necessary to complete a benzoxazole nucleus, a benzothiazole nucleus, a benzoselenazole nucleus, a benzotellurazole nucleus, or a benzimidazole nucleus, which, in addition to being substituted by F, may be further substituted or unsubstituted, R represents H or substituted or unsubstituted alkyl or aryl, R₁ and R₂ each independently represents substituted or unsubstituted alkyl or aryl, R₃ represents an aryl group that may be appended to or fused with Z₁, and X is a counterion as needed to balance the charge of the molecule.

Description: This invention relates to photography, and specifically to spectral sensitization of silver halide emulsions. Silver halide photography usually involves the exposure of silver halide with light in order to form a latent image that is developed during photographic processing to form a visible image. Silver halide is intrinsically sensitive only to light in the blue region of the spectrum. Thus, when silver halide is to be exposed to other wavelengths of radiation, such as green or red light in a multicolor element or infrared radiation in an infrared-sensitive element, a spectral sensitizing dye is required. Sensitizing dyes are chromophoric compounds (usually cyanine dye compounds) that are adsorbed to the silver halide. They absorb light or radiation of a particular wavelength and transfer the energy to the silver halide to form the latent image, thus effectively rendering the silver halide sensitive to radiation of a wavelength other than the blue intrinsic sensitivity. Silver halide is often spectrally sensitized with certain trimethine cyanine dyes, also called carbocyanines. In order to provide high sensitivity and also to provide sensitivity at the proper wavelength of radiation, it is often desirable for the sensitizing dye molecules to aggregate when used to sensitize silver halide emulsions. Carbocyanines that form such aggregates are well-known in the art. One such known dye has the formula: Dyes, such as the one shown above, although they form an aggregate such as a J-aggregate so as to provide high photographic sensitivity and good spectral absorbance characteristics, also suffer from the disadvantage that they tend to be retained in the layers of the photographic material after processing, leading to undesirable dye stain. The prior art has generally used stain-reducing agents, such as bis-triazine stilbene compounds known as optical brighteners, in order to reduce this retained dye stain. These compounds, however, are expensive and can be difficult to incorporate in the hydrophilic layers in photographic materials. On the other hand, dyes, such as: tend to have low stain, but do not aggregate to an extent sufficient to provide the desired spectral sensitivity to silver halide emulsions. It is thus an object of this invention to spectrally sensitize silver halide photographic compositions with a carbocyanine dye that provides high sensitivity, yet also provides low stain while avoiding the necessity of using stain-reducing agents. According to the invention, silver halide photographic compositions are spectrally sensitized with a dye according to the formula: wherein Z₁ represents the atoms necessary to complete a benzoxazole nucleus, a benzothiazole nucleus, a benzoselenazole nucleus, a benzotellurazole nucleus, or a benzimidazole nucleus, which, in addition to being substituted by R₃ and the substituent on the N atom, may be further substituted or unsubstituted, Z₂ represents the atoms necessary to complete a benzoxazole nucleus, a benzothiazole nucleus, a benzoselenazole nucleus, a benzotellurazole nucleus, or a benzimidazole nucleus, which, in addition to being substituted by F and the substituent on the N atom, nay be further substituted or unsubstituted, R represents H or substituted or unsubstituted alkyl or aryl, R₁ and R₂ each independently represents substituted or unsubstituted alkyl or aryl, R₃ represents an aryl group that may be appended to or fused with Z₁, and X is a counterion as needed to balance the charge of the molecule. Dyes comprising a fluoro substituted benzimidazole nucleus and elements containing them are disclosed in US-A-4 789 626 and DE-B-11 80 241. The dye of formula (I) provides effective spectral sensitization of silver halide photographic compositions, imparting good photographic speed, but exhibiting significantly less post-processing dye stain compared to dyes such as dye (A) above. According to formula (I), Z₁ and Z₂ each independently represents the atoms necessary to complete a benzoxazole nucleus, a benzothiazole nucleus, a benzoselenazole nucleus, a benzotellurazole nucleus, or Z₁ is a benzimidazole nucleus, which, in addition to being substituted by R₃ or F and the substituent on the N atom may be further substituted or unsubstituted. Examples of nuclei useful as Z₁ and Z₂ include a benzothiazole nucleus, e.g., benzothiazole, 4-chlorobenzothiazole, 5-chlorobenzothiazole, 6-chlorobenzothiazole, 7-chlorobenzothiazole, 4-methyl-benzothiazole, 5-methylbenzothiazole, 6-methylbenzothiazole, 5-bromobenzothiazole, 6-bromobenzothiazole, 5-phenylbenzothiazole, 6-phenylbenzothiazole, 4-methoxybenzothiazole, 5-methoxybenzothiazole, 6-methoxybenzothiazole, 5-iodobenzothiazole, 6-iodobenzothiazole, 4-ethoxybenzothiazole, 5-ethoxybenzothiazole, 5-hydroxybenzothiazole, 6-hydroxybenzothiazole, or, when R₃ is fused with Z₁, a naphtho[2,1-d]thiazole, naptho[1,2-d]thiazole, 5-methoxynaphtho[2,3-d]thiazole, 5-ethoxynaphtho[2,3-d]thiazole, 8-methoxynaphtho[2,3-d]thiazole, 7-methoxy-naphtho[2,3-d]thiazole; a benzoxazole nucleus, e.g., benzoxazole, 5-chlorobenzoxazole,, a ethylbenzoxazole, 5-phenylbenzoxazole, 6-methylbenzoxazole, 4,6-dimethylbenzoxazole 5-ethoxybenzoxazole, 5-chlorobenzoxazole, 6-methoxybenzoxazole, 5-hydroxybenzoxazole, 6-hydroxybenzoxazole, or, when R₃ is fused with Z₁, a naphtho[2,1-d]oxazole, naphtho[1,2-d]oxazole, etc.; a benzoselenazole nucleus, e.g., benzoselenazole, 5-chlorobenzoselenazole, 5-methoxybenzoselenazole, 5-hydroxybenzoselenazole, or, when R₃ is fused with Z₁, a naphtho[2,1-d]selenazole, naphtho[1,2-d]selenazole, etc.; a benzotellurazole nucleus, e.g., benzotellurazole, naphtho[1,2-d]tellurazole 5,6-dimethoxytellurazole, 5-methoxytellurazole, 5-methyltellurazole. Examples of further nuclei useful as Z₁ are benzimidazole nucleus, e.g., 1-methylbenzimidazole, 1-ethyl-benzimidazole, 1-methyl-5-chlorobenzimidazole, 1-methyl-5-chlorobenzimidazole, 1-ethyl-5-fluorobenzimidazole, 1-allyl-5-chlorobenzimidazole, 1-phenylbenzimidazole, 1-phenyl-5-chlorobenzimidazole, 1-methyl-5-trifluorobenzimidazole, 1-ethyl-5-trifluoromethylbenzimidazole. Also according to formula (I), R₁ and R₂ may be substituted or unsubstituted aryl (preferably of 6 to 15 carbon atoms), or more preferably, substituted or unsubstituted alkyl (preferably of from 1 to 6 carbon atoms). Examples of aryl include phenyl, tolyl, p -chlorophenyl, and p -methoxyphenyl. Examples of alkyl include methyl, ethyl, propyl, isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., and substituted alkyl groups (preferably a substituted lower alkyl containing from 1 to 6 carbon atoms), such as a hydroxyalkyl group, e.g., β-hydroxyethyl, ω-hydroxybutyl, etc., an alkoxyalkyl group, e.g., β-methoxyethyl, ω-butoxybutyl, etc., a carboxyalkyl group, e.g., β-carboxyethyl, ω-carboxybutyl, etc.; a sulfoalkyl group, e.g., β-sulfoethyl, ω-sulfobutyl, etc., a sulfatoalkyl group, e.g., β-sulfatoethyl, ω-sulfatobutyl, etc., an acyloxyalkyl group, e.g., β-acetoxyethyl, γ-acetoxypropyl, ω-butyryloxbutyl, etc., an alkoxycarbonylalkyl group, e.g., β-methoxycarbonylethyl, ω-ethoxycarbonylbutyl, etc., or an aralkyl group, e.g., benzyl, phenethyl, etc. The alkyl or aryl group may be substituted by one or more of the substituents on the above-described substituted alkyl groups. In a preferred embodiment, at least one and preferably both of R₁ and R₂ are substituted with acid salt substituents (e.g., sulfo), as this tends to even further reduce post-processing retained dye stain. R represents H, substituted or unsubstituted alkyl (preferably lower alkyl of 1 to 6 carbon atoms, e.g., methyl, ethyl) or substituted or unsubstituted aryl (e.g., phenyl). In a preferred embodiment, R is ethyl. This is because one of the advantages provided by the dyes of formula (I) is that they can be chosen so as to J-aggregate, while providing lower retained dye stain than prior art J-aggregating dyes such as 5-chloro-substituted dyes. Dyes according to formula (I) where R is ethyl tend to J-aggregate, and thus, R is preferably ethyl. R₃ represents a substituted or unsubstituted aromatic ring that is fused with or appended to Z₁. Examples of aromatic rings that may be appended to Z₁ include substituted or unsubstituted phenyl, substituted or unsubstituted pyridyl, thienyl, pyrrole, furanyl, or styryl. Substituents for these R₃ groups include hydroxy, alkoxy, aryloxy, alkyl, halogen, cyano, and the like. In a preferred embodiment, R₃ is appended to the 5-position of the Z₁ ring structure or fused with the 4,5-positions of the Z₁ ring structure. X represents a counterion as necessary to balance the charge of the dye molecule. The counterion may be ionically complexed to the molecule or it may be part of the dye molecule itself to form an intramolecular salt. Such counterions are well-known in the art. For example, when X is an anion (e.g., when R₁ and R₂ are unsubstituted alkyl), examples of X include chloride, bromide, iodide, p -toluene sulfonate, methane sulfonate, methyl sulfate, ethyl sulfate, perchlorate, and the like. When X is a cation (e.g., when R₁ and R₂ are both sulfoalkyl or carboxyalkyl), examples of X include sodium, potassium, triethylammonium, and the like. Examples of dyes according to formula (I) are set forth below. The amount of sensitizing dye of formula (I) that is useful in the invention is preferably in the range of 0.1 to 1.0 millimoles per mole of silver halide and more preferably from 0.2 to 0.7 millimoles per mole of silver halide. Optimum dye concentrations can be determined by methods known in the art. The dyes of formula (I) can be synthesized by techniques known in the art, such as described in Hamer, Cyanine Dyes and Related Compounds , 1964 and James, The Theory of the Photographic Process 4th, 1977. The synthesis of a representative dyes of formula (I) is set forth in the Examples below. The silver halide that can be sensitized by the dye of formula (I) can be of any known type, such as silver bromoiodide, silver bromide, silver chloride, silver chlorobromide, and the like. In a preferred embodiment, the dye is used to sensitize silver halide emulsions that are high in chloride, preferably above about 80 mole percent and more preferably above about 95 mole percent. Such high-chloride emulsions are often subjected to rapid processing, which further increases the need for low-staining dyes. The type of silver halide grain used in the invention is not critical and essentially any type of silver halide grains can be used in the practice of the invention, although since the dye is lower stain than prior art aggregating dyes, it may be advantageously used in combination with tabular grain emulsions, which have greater surface area, allowing for greater amounts of dye to be used. The grain size of the silver halide may have any distribution known to be useful in photographic compositions, and may be either polydisperse or monodisperse. The mean grain diameter is preferably from 0.05 µm to 1.5 µm. The silver halide grains to be used in the invention may be prepared according to methods known in the art, such as those described in Research Disclosure , Item 308119, December, 1989 [hereinafter referred to as Research Disclosure I ] and Mees, The Theory of the Photographic Process . These include methods such as ammoniacal emulsion making, neutral or acid emulsion making, and others known in the art. These methods generally involve mixing a water soluble silver salt with a water soluble halide salt in the presence of a protective colloid, and controlling the temperature, pAg, pH values, etc, at suitable values during formation of the silver halide by precipitation. The silver halide to be used in the invention may be advantageously subjected to chemical sensitization with compounds such as gold sensitizers (e.g., aurous sulfide) and others known in the art. Compounds and techniques useful for chemical sensitization of silver halide are known in the art and described in Research Disclosure I and the references cited therein. The silver halide may be sensitized by the dye of formula (I) by any method known in the art, such as described in Research Disclosure I . The dye may added to an emulsion of the silver halide grains and a hydrophilic colloid at any time prior to (e.g., during or after chemical sensitization) or simultaneous with the coating of the emulsion on a photographic element. The dye/silver halide emulsion may be mixed with a dispersion of color image-forming coupler immediately before coating or in advance of coating (e.g., 2 hours). The dye of formula (I) may be used by itself to sensitize silver halide, or it may be used in combination with other sensitizing dyes to provide the silver halide with sensitivity to broader or different ranges of wavelengths of light than silver halide sensitized with a single dye, or to in a supersensitizing combination with other sensitizing dyes. In a preferred embodiment of the invention, the dye of formula (I) is used to sensitize silver halide in photographic emulsions, which can be coated as layers on photographic elements. Essentially any type of emulsion can be used (e.g., negative-working emulsions such as surface-sensitive emulsions or unfogged internal latent image-forming emulsions, direct-positive emulsions such as surface fogged emulsions, or others described in, for example, Research Disclosure I . Photographic emulsions generally include a vehicle for coating the emulsion as a layer of a photographic element. Useful vehicles include both naturally occurring substances such as proteins, protein derivatives, cellulose derivatives (e.g., cellulose esters), gelatin (e.g., alkali-treated gelatin such as cattle bone or hide gelatin, or acid treated gelatin such as pigskin gelatin), gelatin derivatives (e.g., acetylated gelatin, phthalated gelatin, and the like), and others as described in Research Disclosure I . Also useful as vehicles or vehicle extenders are hydrophilic water-permeable colloids. These include synthetic polymeric peptizers, carriers, and/or binders such as poly(vinyl alcohol), poly(vinyl lactams), acrylamide polymers, polyvinyl acetals, polymers of alkyl and sulfoalkyl acrylates and methacrylates, hydrolyzed polyvinyl acetates, polyamides, polyvinyl pyridine, methacrylamide copolymers, and the like, as described in Research Disclosure I . The vehicle can be present in the emulsion in any amount known to be useful in photographic emulsions. The emulsion can also include any of the addenda known to be useful in photographic emulsions. These include chemical sensitizers, such as active gelatin, sulfur, selenium, tellurium, gold, platinum, palladium, iridium, osmium, rhenium, phosphorous, or combinations thereof. Chemical sensitization is generally carried out at pAg levels of from 5 to 10, pH levels of from 5 to 8, and temperatures of from 30 to 80°C, as illustrated in Research Disclosure, June, 1975, item 13452 and U.S. Patent 3,772,031. Other addenda include antifoggants, stabilizers, filter dyes, light absorbing or reflecting pigments, vehicle hardeners such as gelatin hardeners, coating aids, dye-forming couplers, and development modifiers such as development inhibitor releasing couplers, timed development inhibitor releasing couplers, and bleach accelerators. These addenda and methods of their inclusion in emulsion and other photographic layers are well-known in the art and are disclosed in Research Disclosure I and the references cited therein. The emulsion may also include brighteners, such as stilbene brighteners. Alternatively, such brighteners may be contained in processing solutions. Such brighteners are well-known in the art and are used to counteract dye stain, although the dyes of formula (I) offer reduced dye stain even if no brightener is used. The emulsion layer containing silver halide sensitized with the dye of formula (I) can be coated simultaneously or sequentially with other emulsion layers, subbing layers, filter dye layers, interlayers, or overcoat layers, all of which may contain various addenda known to be included in photographic elements. These include antifoggants, oxidized developer scavengers, DIR couplers, antistatic agents, optical brighteners, light-absorbing or light-scattering pigments, and the like. The layers of the photographic element can be coated onto a support using techniques well-known in the art. These techniques include immersion or dip coating, roller coating, reverse roll coating, air knife coating, doctor blade coating, stretch-flow coating, and curtain coating, to name a few. The coated layers of the element may be chill-set or dried, or both. Drying may be accelerated by known techniques such as conduction, convection, radiation heating, or a combination thereof. Photographic elements comprising the composition of the invention can be black and white or color. A color photographic element generally contains three silver emulsion layers or sets of layers: a blue-sensitive layer having a yellow color coupler associated therewith, a green-sensitive layer having a magenta color coupler associated therewith, and a red-sensitive layer having a cyan color coupler associated therewith. The dye of formula (I) is advantageously utilized in a green-sensitive layer of a color photographic element having a magenta dye-forming color coupler associated therewith. Any of the known magenta couplers, such as the one shown in the example below(or, alternatively the coupler shown in the example, but having a substituent other than hydrogen at the coupling-off position of the pyrazolone ring) may be used. Alternatively, the dyes of formula (I) may be red sensitizing dyes utilized in a red-sensitive layer of a color photographic element having a cyan dye-forming coupler associated therewith. These color image-forming couplers along with other element configurations are well-known in the art and are disclosed, for example, in Research Disclosure I . Photographic elements comprising the composition of the invention can be processed in any of a number of well-known photographic processes utilizing any of a number of well-known processing compositions, described, for example, in Research Disclosure I or in James, The Theory of the Photographic Process 4th, 1977. Elements having high chloride silver halide photographic compositions are especially advantageously processed by fast processes utilizing a so-called rapid access developer, as described in the Photographic Examples below. The invention is described further in the following Examples. Synthesis Example 1 - Preparation of Dye 2 1 g of a compound having the formula: and 1 g of a compound having the formula: were mixed in 5 ml m-cresol and heated to 120°C. Triethylamine (5ml) was added with stirring. After 5 minutes, the mixture was cooled and poured into ether. The mixture was washed three times with ether, and the oil was dissolved in 20 ml CH₃CN. Water (3 ml) containing 0.4 g potassium acetate was added, causing the dye to precipitate. The mixture was heated to reflux, and then chilled. The precipitate was collected and purified with an HPLC column using a mixture of H₂O and CH₃CN. λ-max (methanol) = 506 nm, ε-max = 12.7 X 10⁴. Photographic Examples Dye 1 and a comparison dye having the structure: were used to sensitize a silver halide emulsion. The emulsion was an aurous sulfide sensitized 0.31 µm silver chloride emulsion having the following coverages on a polyester support. silver 280 mg/m² gelatin 1.66 g/m² 1-(3-acetamidophenyl)-5-mercaptotetrazole 380 mg/mole Ag KBr 63.6 mg/mole Ag KCl 8.1 g/mole Ag magenta coupler 448 mg/m² The magenta coupler had the structure: The coupler dispersion was added to the dye/silver chloride emulsion immediately before coating. The elements also included a gelatin overcoat layer (1.08 g/m²) and a gelatin undercoat layer (1.08 g/m²) above and below the emulsion layer. To evaluate photographic sensitivity, the elements were exposed to a 3000°K tungsten light source with ultraviolet and heat-absorbing filters, and processed as described below. For retained dye stain evaluation, identical but unexposed elements were subjected to the same processing, and the optical density at 510 nm was measured. Process: 40 sec in developer 5 sec drain 45 sec Kodak Ektaprint2® blix 3 min wash dry Developer composition: p-phenylenediamine developing agent 5.0 g sulfonated polystyrene 0.25 ml triethanolamine 11.0 ml diethylhydroxylamine (85%) 6 0 ml lithium sulfate 2.7 g anti-calcium agent 0.8 ml potassium chloride 1.6 g potassium bromide 10.0 mg potassium carbonate 25.0 g water to make 1.0 l adjust pH to 10.0 The photographic speeds and retained dye stain measurements are presented in Table I below. The dye level is presented as a fraction times the base level of 4.75 X 10⁻⁴ mmole/mole Ag. Dye Level White Light Speed Dye Stain (density) A 0.7X 175 0.023 A 0.85X 185 0.028 A 1.0X 182 0 029 A 1.15X 190 0.033 1 0.7X 174 0.012 1 0.85X 179 0.013 1 1.0X 181 0.017 1 1.15X 183 0.018 The data presented in Table I demonstrate that the dye of formula (I) provided comparable photographic speed as the comparison dye, but with significantly less retained dye stain.

Claims: A photographic element comprising a support having thereon at least one silver halide emulsion layer comprising silver halide spectrally sensitized with a dye, characterized in that the dye has the formula: wherein Z₁ represents the atoms necessary to complete a benzoxazole nucleus, a benzothiazole nucleus, a benzoselenazole nucleus, a benzotellurazole nucleus, or a benzimidazole nucleus, which, in addition to being substituted by R₃ and the substituent on the N atom, may be further substituted or unsubstituted, Z₂ represents the atoms necessary to complete a benzoxazole nucleus, a benzothiazole nucleus, a benzoselenazole nucleus, or a benzotellurazole nucleus, which, in addition to being substituted by F and the substituent on the N atom, may be further substituted or unsubstituted, R represents H or substituted or unsubstituted alkyl or aryl, R₁ and R₂ each independently represents substituted or unsubstituted alkyl or aryl, R₃ represents an aryl group that may be appended to or fused with Z₁, and X is a counterion as needed to balance the charge of the molecule, A photographic element according to claim 1 further characterized in that R₃ represents an aryl group fused with the Z₁ nucleus to form a substituted or unsubstituted: naphtho[1,2-d]oxazole nucleus, naphtho[1,2-d]thiazole nucleus, naphtho[1,2-d]-selenazole nucleus, or naphtho[1,2-d]benzimidazole nucleus. A photographic element according to claims 1 or 2 further characterized in that F is appended to the 5-position of the Z₂ nucleus. A photographic element according to claims 1 or 2 further characterized in that at least one of R₁ and R₂ are alkyl substituted with an acid or acid salt group. A photographic element according to claims 1 or 2 further characterized in that both of R₁ and R₂ are alkyl substituted with an acid or acid salt group. A photographic element according to claim 3 further characterized in that both of R₁ and R₂ are alkyl substituted with an acid or acid salt group. A photographic element according to claim 1 further characterized in that the dye has the formula: wherein Y and Y' each independently represents O, S, or Se, R₄ and R₅ each independently represents alkyl substituted with an acid or acid salt group, R₆ represents an aryl group that may be appended to or fused with the ring to which it is attached, and X is a counterion as needed to balance the charge of the molecule. A compound characterized in having the formula: wherein Z₁ represents the atoms necessary to complete a benzoxazole nucleus, a benzothiazole nucleus, a benzoselenazole nucleus, a benzotellurazole nucleus, or a benzimidazole nucleus, which, in addition to being substituted by R₃ and the substituent on the N atom, may be further substituted or unsubstituted, Z₂ represents the atoms necessary to complete a benzoxazole nucleus, a benzothiazole nucleus, a benzoselenazole nucleus, or a benzotellurazole nucleus, which, in addition to being substituted by F and the substituent on the N atom, may be further substituted or unsubstituted, R represents H or substituted or unsubstituted alkyl or aryl, R₁ and R₂ each independently represents substituted or unsubstituted alkyl or aryl, R₃ represents an aryl group that may be appended to or fused with Z₁, and X is a counterion as needed to balance the charge of the molecule. A compound according to claim 8 further characterized in that the compound has the formula: wherein Y and Y' each independently represents O, S, or Se, R₄ and R₅ each independently represents alkyl substituted with an acid or acid salt group, R₆ represents an aryl group that may be appended to or fused with the ring to which it is attached, and X is a counterion as needed to balance the charge of the molecule.

Inventors: MACINTYRE GLADYS L C O EASTMAN, PARTON RICHARD LEE C O EASTMAN, WEBER WAYNE WOODROW C O EASTMA, MACINTYRE, GLADYS L., C/O EASTMAN KODAK COMPANY, PARTON, RICHARD LEE, C/O EASTMAN KODAK COMPANY, WEBER, WAYNE WOODROW, C/O EASTMAN KODAK COMPANY
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1991
Main classification: G03C1
IPC codes: G03C1, C09B23