Desensitizing dyes for photographic emulsions

Novel cyanine dye salts having an alkoxyaryl function joined by a vinylene linkage to a heterocyclic nucleus are useful as desensitizers in fogged, direct positive type of silver halide emulsions.

TECHNICAL FIELD 
This invention relates to a new class of cyanine dye salts and their use as 
desensitizers in direct positive photographic emulsions. 
BACKGROUND ART 
Cyanine dyes useful as desensitizers in a fogged, direct positive type of 
silver halide emulsion are known. U.S. Pat. No. 3,431,111 discloses 
certain cyanine dyes which contain an imidazo[4,5-b]quinoxaline nucleus. 
U.S. Pat. No. 4,025,347 discloses certain cyanine dyes containing an 
indole or indolenine nucleus carrying in the phenyl ring thereof a 
substituent of the benzoyl or phenyl-sulfonyl type. 
DISCLOSURE OF THE INVENTION 
The new class of cyanine dye salts of the present invention comprises 
compounds in which an alkoxyaryl function is joined by a vinylene 
(--CH.dbd.CH--) linkage to a heterocyclic nucleus. These dye salts, used 
in a chemically effective desensitizing amount, are useful as 
desensitizers in fogged, direct positive silver halide emulsions. 
The desensitizing dyes of the present invention include compounds of the 
general formula 
##STR1## 
wherein L represents a carbocyclic ligand, said ligand comprising a 
monocyclic nucleus of up to 6 carbon atoms, or polycyclic fused nuclei 
(i.e., wherein the nuclei share at least 2 common ring atoms) having at 
least one 6-membered ring, the cyclic carbon atoms of said ligand having 
up to 5 alkoxy substituents, each substituent having up to 4 carbon atoms, 
Z represents a group of nonmetallic atoms required to complete a 
desensitizing heterocyclic nucleus containing five atoms in a heterocyclic 
ring which may contain a second hetero atom such as oxygen, sulfur, 
selenium, or nitrogen, and said ring is part of a fused ring system of up 
to 3 rings, which ring system may contain up to 4 hetero atoms, and with 
no individual ring having more than 6 ring atoms, 
R.sup.1 represents a phenylsulfonyl, hydrogen, alkyl of up to 4 carbon 
atoms, or a nitro group that occupies the 5-position in a double fused 
ring system or the 6-position in a triple fused ring system, and 
X.sup..crclbar. represents an acid anion. 
Z includes heterocyclic ring systems based on thiazole or benzothiazole 
(e.g., 5-chlorobenzothiazole, 5-nitrobenzothiazole, 
5-benzoylbenzothiazole); indolenine (e.g., 3,3-dimethyl-5-nitroindolenine, 
3,3-dimethyl-5-phenylsulfonylindolenine, 
3,3-dimethyl-5-benzoylindolenine); imidazo[4,5-b]quinoxaline (e.g., 
imidazo[4,5-b]quinoxaline, 6-methylimidazo[4,5-b]quinoxaline, 
6,7-dimethylimidazo[4,5-b]quinoxaline, 6-nitroimidazo[4,5-b]quinoxaline, 
6,7-dichloroimidazo[4,5-b]quinoxaline); 
imidazo[4,5-b]pyrido[2,3-b]pyrazine; and 3-ethyl thiazolo[4,5-b]quinoline. 
Preferably X.sup..crclbar. is an anion such as chloride, bromide, iodide, 
p-toluenesulfonate, methylsulfate, ethyl sulfate, and perchlorate. 
DETAILED DESCRIPTION 
In one embodiment, the new class of cyanine dye salts of the present 
invention comprise compounds in which the alkoxyaryl function is joined 
through a vinylene linkage to the 2-position of an imidazoquinoxalino 
nucleus. 
In a second embodiment of this invention, the alkoxyaryl function is joined 
through a vinylene linkage to the 2-position of a phenyl-sulfonyl indole 
nucleus. 
In a third embodiment of this invention, the alkoxyaryl function is joined 
through a vinylene linkage to the 2-position of a benzothiazole nucleus. 
Aryl as used herein refers to the monovalent phenyl radical (C.sub.6 
H.sub.5 --) and the monovalent naphthyl radical (C.sub.10 H.sub.7 --). The 
phenyl function may be mono, di, tri, or tetraalkoxyl substituted and 
preferably it is a trimethoxy phenyl function. The alkoxy group is lower 
alkoxy containing up to four carbon atoms. 
This invention, in addition to disclosure of this class of novel cyanine 
dye salts, relates to methods for preparing these new dyes and to 
photographic emulsions containing desensitizing amounts of these new dyes. 
Briefly, the new dyes of the present invention include those represented by 
the following general formulae: 
##STR2## 
wherein: R represents an alkyl group of 1 to 4 carbon atoms, and 
preferably it is a --CH.sub.3 or --C.sub.2 H.sub.5 group, 
R.sup.1 represents an alkyl group of 1 to 4 carbon atoms, and preferably it 
is a --C.sub.2 H.sub.5 group, 
R.sup.2, R.sup.3, and R.sup.4 each independently represent a hydrogen atom 
or an alkoxy group of up to 4 carbon atoms which preferably is a 
--OCH.sub.3 or --OC.sub.2 H.sub.5 group, 
R.sup.5 and R.sup.6 each independently represent a hydrogen atom or an 
alkoxy group of up to 4 carbon atoms which preferably is a --OCH.sub.3 
group, or R.sup.5 and R.sup.6 may be the substituents necessary to form a 
fused benzene ring which may itself be further substituted by an alkoxy 
group of up to 4 carbon atoms, which preferably is a --OCH.sub.3 group, 
with the proviso that at least one of R.sup.2, R.sup.3, R.sup.4, R.sup.5, 
and R.sup.6 is selected from alkoxy groups, which preferably is a 
--OCH.sub.3 or --OC.sub.2 H.sub.5 group, 
R.sup.7 and R.sup.8 each independently represent a hydrogen atom or an 
alkyl group of up to 4 carbon atoms which preferably is a --CH.sub.3 
group, 
R.sup.9 represents a --NO.sub.2 group, 
Y represents a N, or S atom, and preferably is a S atom, and 
X represents an acid anion, for instance chloride, bromide, iodide, 
sulfonate, perchlorate, p-toluenesulfonate, methylsulfate, etc., and 
preferably is an iodide or p-toluene-sulfonate group. 
The cyanine dyes of the present invention may all be prepared by aldehyde 
condensation with the quaternary salt of the appropriate 
imidazoquinoxaline, phenylsulfonylindole, or benzothiazole compound. The 
appropriate aldehyde is heated with an active methylene group-containing 
compound in acetic anhydride for several hours. The desired product is 
separated by filtration. 
The present invention provides direct positive photographic silver halide 
emulsions which, as is known in the art, are prepared by incorporating one 
or more of the cyanine dyes of the invention into a suitable fogged silver 
halide emulsion. The emulsion can be fogged in any appropriate manner, 
such as by light or with chemical fogging agents, e.g., stannous chloride, 
formaldehyde, or thiourea dioxide. The emulsion may be fogged by the 
addition thereto of a reducing agent, such as thiourea dioxide, and a 
compound of a metal more electropositive than silver, such as a gold salt. 
Examples include potassium chloraurate, auric chloride, and 
(NH.sub.4).sub.2 PdCl.sub.6. 
Useful concentrations of reducing agent and metal compound can be varied 
over a considerable range. Good results are obtained using about 0.05 to 
40 mg. reducing agent per mole of silver halide and 0.5 to 15.0 mg. metal 
compound per mole of silver halide. Best results are obtained at lower 
concentration levels of both reducing agent and metal compound. 
The concentration of added dye can vary widely, e.g., from about 100 to 
1000 mg. and preferably from about 250 to 500 mg. per mole of silver 
halide in the direct positive emulsions. 
In the preparation of the above photographic emulsions, the dyes of the 
invention are advantageously incorporated in the washed, finished silver 
halide emulsion and should be uniformly distributed throughout the 
emulsion. The methods of incorporating dyes and other addenda in emulsions 
are well known to those skilled in the art of emulsion making. For 
example, it is convenient to add them from solutions in appropriate 
solvents; the solvent selected should be completely free from any 
deleterious effect on the ultimate light-sensitive materials. Satisfactory 
solvents for this purpose include methanol, isopropanol, pyridine, and 
water, alone or in admixtures. The type of silver halide emulsions that 
can be sensitized with the new dyes include any of those prepared with 
hydrophilic colloids that are known to be useful for dispersing silver 
halides, for example, emulsions comprising natural materials such as 
gelatin, albumin, gum arabic, and hydrophilic synthetic resins such as 
polyvinyl alcohol and polyvinyl pyrrolidone. 
The binding agents for the emulsion layer of the photographic element can 
also contain dispersed polymerized vinyl compounds such as water insoluble 
polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl 
acrylates or methacrylates. 
The dyes, reducing agents and metal compounds of the invention can be used 
with emulsions prepared with any of the light-sensitive silver halide 
salts including silver chloride, silver bromide, silver chlorobromide, 
silver bromoiodide, silver chlorobromoiodide, etc. 
The novel emulsions of this invention may be coated on any suitable 
photographic support, such as glass, polymeric films such as cellulose 
acetate, polystyrenes, polyesters such as poly(ethylene terephthalate), 
paper and coated paper. 
The compounds of the present invention provide new and improved light 
sensitive photographic emulsions, such as fogged, direct, positive 
emulsions typically used in graphic arts films and color photographic 
films.

Objects and advantages of this invention are further illustrated by the 
following examples, but the particular materials and amounts thereof 
recited in these examples, as well as other conditions and details, should 
not be construed to unduly limit this invention. 
EXAMPLE 1 
1,3-diethyl-2-[(2',4',6'-trimethoxyphenyl)vinyl]imidazo[4,5-b]quinoxalinium 
-p-toluenesulfonate 
##STR3## 
A mixture of (0.82 g, 0.0020 mole) 
1,3-diethyl-2-methylimidazo[4,5-b]quinoxalinium-p-toluenesulfonate, having 
the formula, 
##STR4## 
prepared as described in U.S. Pat. No. 3,431,111 or U.S. Pat. No. 
3,632,808, and 2,4,6-trimethoxybenzaldehyde (0.40 g, 0.0020 mole) was 
boiled in 1.5 ml acetic anhydride for 10 min. Upon cooling the red 
solution gave a yellow precipitate which was collected and then washed 
with ethyl acetate and ether to give 0.63 g of product, m.p. 
241.degree.-242.degree. C. Spectral analysis confirmed the product to be 
1,3-diethyl-2-[(2',4',6'-trimethoxyphenyl)vinyl]imidazo[4,5-b]quinoxaliniu 
m-p-toluenesulfonate. 
EXAMPLE 2 
1,3-diethyl-6,7-dimethyl-2-[(2',4',6'-trimethoxyphenyl)vinyl]imidazo[4,5-b] 
quinoxalinium-p-toluenesulfonate 
##STR5## 
Using the same general methods as in Example 1, except that 
1,3-diethyl-2,6,7-trimethylimidazo[4,5-b]quinoxalinium-p-toluenesulfonate, 
prepared by the method described in U.S. Pat. No. 3,431,111, and 
2,4,6-trimethoxybenzaldehyde were used as starting materials and ethyl 
acetate was added to precipitate the product from the reaction mixture, 
m.p. 235.degree.-236.degree. C. Spectral analysis confirmed the compound 
to be 
1,3-diethyl-6,7-dimethyl-2-[(2',4',6'-trimethoxyphenyl)vinyl]imidazo[4,5-b 
]quinoxalinium-p-toluenesulfonate. 
EXAMPLE 3 
1-ethyl-3,3-dimethyl-5-phenylsulfonyl-2-[(2',4',6'-trimethoxyphenyl)vinyl]i 
ndoleninium iodide 
##STR6## 
Using the same general method as in Example 2, except that 
1-ethyl-2,3,3-trimethyl-5-phenylsulfonylindoleninium iodide, prepared as 
disclosed in Example 22 of U.S. Pat. No. 4,025,347, was used as a starting 
material, a solid compound (m.p. 178.degree.-180.degree. C.) was collected 
from the reaction mixture. Spectral analysis confirmed the compound to be 
1-ethyl-3,3-dimethyl-5-phenylsulfonyl-2-[(2',4',6'-trimethoxyphenyl)vinyl] 
indoleninium iodide. 
EXAMPLE 4 
1-ethyl-5-nitro-2-[(2',4',6'-trimethoxyphenyl)vinyl]benzothiazolium iodide 
##STR7## 
Using the same general method as in Example 1, except that 
1-ethyl-2-methyl-5-nitrobenzothiazolium iodide, 
##STR8## 
prepared as described in J. Am. Chem. Soc., 64, 207 (1942), was used as 
starting materials, a solid compound (m.p. 271.degree.-272.degree. C.) was 
collected from the mixture. Spectral analysis confirmed the compound to be 
1-ethyl-5-nitro-2-[(2',4',6'-trimethoxyphenyl)vinyl]benzothiazolium 
iodide. 
EXAMPLE 5 
In a similar manner as in Examples 1 and 2, the sample compounds of Table I 
were prepared. Spectral analysis was used to confirm the structures. 
The mono, di, and trimethoxybenzaldehydes and methoxynaphthaldehydes were 
all obtained from Aldrich Chemical Co. 
The 2,3,4,6-tetramethoxybenzaldehyde was prepared from tetramethoxybenzene 
as described in J. Chem. Soc., 1974, 1353. 
Tetramethoxybenzene was prepared as described in J. Chem. Soc., 1941, 665. 
The 2,4,5-triethoxybenzaldehyde was obtained from the Alfred Bader Library 
of Rare Chemicals, Aldrich Chemical Co. 
The 2,4,6-triethoxybenzaldehyde was obtained from the Chemicals Procurement 
Laboratories. 
TABLE I 
__________________________________________________________________________ 
SAM- 
PLE 
NO. STRUCTURE NAME M.P. 
__________________________________________________________________________ 
##STR9## 1,3-diethyl-2-[(2',3',4',6'-tetr 
a- methoxyphenyl)vinyl]imidazo- 
[4,5-b]quinoxalinium-p-toluene- 
ulfonate 204-206.degree. 
C. 
6 
##STR10## 1-ethyl-3,3-dimethyl-5-phenyl- 
sulfonyl-2-[(2',3',4',6'-tetra- 
ethoxyphenyl)vinyl] indoleninium 
iodide 195.degree. C. 
7 
##STR11## 1-ethyl-5-nitro-2-[(2',3',4',6'- 
tetramethoxyphenyl)vinyl]- 
benzothiazolium 
231-233.degree. 
C. 
8 
##STR12## 1-ethyl-3,3,-dimethyl-4-phenyl- 
ulfonyl-2-[(2',4'-dimethoxy- 
phenyl)vinyl]indoleninium 
iodide 232-234.degree. 
C. 
9 
##STR13## 1-ethyl-3,3-dimethyl-5-phenyl- 
sulfonyl-2-[(2',5'-dimethoxy- 
phenyl)vinyl]indoleninium 
iodide 191-192.degree. 
C. 
10 
##STR14## 1-ethyl-3,3-dimethyl-5-phenyl- 
sulfonyl-2-[(4'-methoxy-1'-naph- 
thyl)vinyl]indoleninium 
165-168.degree. 
C. 
11 
##STR15## 1-ethyl-3,3-dimethyl-5-phenyl- 
sufonyl-2-[(2'-methoxy-1'naph- 
thyl)vinyl]indoleninium 
207-208.degree. 
C. 
12 
##STR16## 1,3-diethyl-2-[(2',4',5'-trimeth 
- oxyphenyl)vinyl]imidazo[4,5-b] 
quinoxalinium-p-toluene- 
sulfonate 205-206.degree. 
C. 
13 
##STR17## 1-ethyl-3,3-dimethyl-5-phenyl- 
sulfonyl-2-[(2',4',5'-trimethoxy 
- phenyl)vinyl]indoleninium 
iodide 158-160.degree. 
C. 
14 
##STR18## 1,3-diethyl-2-[(2',4',5'-trietho 
xy- phenyl)vinyl]imidazo[4,5-b]- 
quinoxalinium-p-toluene- 
sulfonate 189-191.degree. 
C. 
15 
##STR19## 1-ethyl-3.3-dimethyl-5-phenyl- 
sulfonyl-2-[(2',4',5'-triethoxy- 
phenyl)vinyl]indoleninium 
iodide 230-231.degree. 
C. 
16 
##STR20## 1,3-diethyl-2-[(2',4',6'-trietho 
xy- phenyl)vinyl]imidazo[4,5-b]- 
quinoxalinium-p-toluene- 
sulfonate 215-217.degree. 
C. 
17 
##STR21## 1-ethyl-3,3-dimethyl-5-phenyl- 
sulfonyl-2-[(2',4',6'-triethoxy- 
phwnyl)vinyl]indoleninium 
iodide 230-231.degree. 
C. 
18 
##STR22## 1,3-diethyl-2-(phenylvinyl)- 
imidazo[4,5-b]quinoxalinium-p- 
toluenesulfonate 
224.degree. C. 
19 
##STR23## 1-ethyl-3,3-dimethyl-5-phenyl- 
sulfonyl-2-(phenylvinyl)- 
indoleninium iodide 
170-171.degree. 
C. 
__________________________________________________________________________ 
EXAMPLE 6 
Coating and emulsion testing data 
A monodisperse cubic Ag(I)Br emulsion containing 3% iodide was prepared by 
the balanced double jet precipitation technique, maintaining a pAg of 3.5. 
After completion of physical ripening the emulsion was coagulated with 
acetic anhydride and the excess halide salts were removed by decanting. 
The washed emulsion was redispersed in gelatin; the pH was adjusted to 8 
and the pAg to 8. The emulsion was fogged by adding formamidinesulfinic 
acid and gold chloride stabilized with hydrochloric acid. After digesting 
at 60.degree. C. for 1 hour the emulsion was cooled to 35.degree. C. and a 
coating aid such as Alkanol B was added. This emulsion was split into 
portions, the dye solutions were added at a level of 500 mg dye per mole 
of silver, and the emulsion was coated on polyester photographic base by 
methods well known in the art. The coatings were exposed in a sensitometer 
(Eastman Kodak, Model 101) using a 0.2 density wedge, 40 sec. exposure, 
with a 0.7 neutral density filter and processed in a lith developer (RAP 
20 processor Log-Etronics) for 18 seconds. 
The processed film showed the following sensitometric responses. The sample 
compounds used are in Table I above. Coating and emulsion testing data are 
in Table II. 
TABLE II 
______________________________________ 
Speed at 0.2 optical density 
SAMPLE over D.sub.min, log e units 
D.sub.max 
______________________________________ 
18 -1.33 4.70 
16 -0.67 3.85 
14 -1.04 4.75 
19 -2.12 4.86 
17 -0.77 3.75 
15 -1.14 4.64 
13 -1.16 4.52 
______________________________________ 
The table shows that great speed increases are obtained with the compounds 
containing --OR groups and particularly with tri-alkoxy substitution in 
the 2,4,6 positions. 
Various modifications and alterations of this invention will become 
apparent to those skilled in the art without departing from the scope and 
spirit of this invention, and it should be understood that this invention 
is not to be unduly limited to the illustrative embodiments set forth 
herein.