US3492123A - Direct positive silver halide emulsions containing carbocyanine dyes having a carbazole nucleus - Google Patents

Description

United States Patent 3,492,123 DIRECT POSITIVE SILVER HALIDE EMULSIONS CONTAINING CARBOCYANINE DYES HAVING A CARBAZOLE NUCLEUS John D. Mee and Donald W. Heseltine, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey N0 Drawing. Filed Jan. 17, 1967, Ser. No. 609,740 Int. Cl. G03c 1/36, 1/10, 1/28 U.S. Cl. 96-106 18 Claims ABSTRACT OF THE DISCLOSURE Cyanine dyes containing a carbazole nucleus are incorporated in direct positive emulsions.

This application is a continuation-in-part of our U.S. patent application Ser. No. 571,695, filed Aug. 11, 1966,

. now abandoned.

This invention relates to novel direct positive photographic materials, and more particularly to new and improved fogged, direct positive photographic silver halide emulsions containing certain unsymmetrical syanine dyes containing a carbazole nucleus.

We have found that certain unsymmetrical cyanine dyes derived from N-substituted carbazole-3-carboxaldehydes are outstanding electron acceptors and spectral sensitizers in direct positive type photographic silver halide emulsions. They provide superior reversal systems especially with fogged silver halide emulsions that are characterized by both good speed and desired sensitivity to radiation in the green to red region of the visible spectrum, that is, up to a wavelength of about 620-680 m with maximum sensitivity occurring in most cases in the region of about 540-580 mg.

It is, accordingly, an object of this invention to provide a new class of improved and novel, direct positive photographic silver halide emulsions, and more particularly fogged emulsions of this type, containing at least one of the unsymmetrical cyanine dyes of the invention. Another object of this invention is to provide novel emulsions as above containing, in addition, a photographic color former. Another object of this invention is to provide novel light-sensitive photographic elements comprising a support material having thereon at least one layer of the novel emulsions of the invention. Other objects of this invention will be apparent from this disclosure and the appended claims.

In accordance with this invention, we prepare our new class of improved and novel, direct positive photographic silver halide emulsions by incorporating one or more of the unsymmetrical dyes of the invention into a suitable fogged silver halide emulsion. The emulsion can be fogged in any suitable manner, such as by light or with chemical fogging agents, e.g., stannous chloride, formaldehyde, thiourea dioxide and the like. 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, for example, potassium chloroaurate, as described in British Patent 723,019 (1955).

Typical reducing agents that are useful in providing such emulsions include stannous salts, e.g., stannous chloride, hydrazine, sulfur compounds such as thiourea dioxide, phosphonium salts as tetra (hydroxymethyl) phosphonium chloride, and the like. Typical useful metal ICC compounds that are more electropositive than silver include gold, rhodium, platinum, palladium, iridium, etc, preferably in the form of soluble salts thereof, e.g., potassium chloroaurate, auric chloride, (NH PdCl and the like.

Useful concentrations of reducing agent and metal compound (e.g., metal salt) can be varied over a considerable range. As a general guideline, good results are obtained using about .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 50 to 2000 mg. and preferably from about 400 to 800 mg. per mole of silver halide in the direct positive emulsions.

As used herein, and in the appended claims, fogged refers to emulsions containing silver halide grains which produce a density of at least 0.5 when developed, Without exposure, for 5 minutes at 68 F. in developer Kodak DK-SO having the composition set forth below, when the emulsion is coated at a silver coverage of 50 mg. to 500 mg. per square foot.

DEVELOPER G. N-methyl-p-aminophenol sulfate 2.5 Sodium sulfite (anhydrous) 30.0 Sodium metaborate 10.0 Potassium bromide 0.5

Water to make 1.01.

The dyes of this invention are also advantageously incorporated in direct positive emulsions of the type in which a silver halide grain has a water-insoluble silver salt center and an outer shell composed of a fogged water insoluble silver salt that develops to silver without exposure. The dyes of the invention are incorporated, preferably, in the outer shell of such emulsions. These emulsions can be prepared in various ways, such as those described in Berriman U.S. patent application Ser. No. 448,467, filed Apr. 15, 1965 now U.S. Patent No. 3,367,- 778. For example, the shell of the grains in such emulsions may be prepared by precipitating over the core grains a light-sensitive water-insoluble silver salt that can be fogged and which fogv is removable by bleaching. The shell is of suflicient thickness to prevent access of the developer used in processing the emulsions of the invention to the core. The silver salt shell is surface fogged to make developable to metallic silver with conventional surface image developing compositions. The silver salt of the shell is sufficiently fogged to produce a density of at least about 0.5 when developed for 6 minutes at 68 F. in Developer A below when the emulsion is coated at a silver coverage of mg. per square foot. Such fogging can be effected by chemically sensitizing to fog with the sensitizing agents described for chemically sensitizing the core emulsion, high intensity light and the like fogging means well known to those skilled in the art. While the more need not be sensitized to fog, the shell is fogged. Fogging by means of a reduction sensitizer, a noble metal salt such as gold salt plus a reduction sensitizer, a sulfur sensitizer, high pH and low pAg silver halide precipitating conditions, and the like can be suitably utilized. The shell portion of the subject grains can also be coated prior to fogging.

3 DEVELOPER A Grams N-methyl-p-aminophenol sulfate 2.5 Ascorbic acid 10.0 Potassium metaborate 35.0 Potassium bromide 1.0

Water to 1 liter. pH of 9.6.

Before the shell of water-insoluble silver salt is added to the silver salt core, the core emulsion is first chemically or physically treated by methods previously described in the prior art to produce centers which promote the deposition of photolytic silver, i.e., latent image nucleating centers. Such centers can be obtained by various techniques as described herein. Chemical sensitization techniques of the type described by Antoine Hautot and Henri Saubeneir in Science et Industries Photographiques, vol. XXVIII, January 1957, pages 1 to 23 and January 1957, pages 57 to 65 are particularly useful. Such chemical sensitization includes three major classes, namely, gold or noble metal sensitization, sulfur sensitization such as by a labile sulfur compound, and reduction sensitization, e.g., treatment of the silver halide with a strong reducing agent which introduces small specks of metallic silver into the silver salt crystal or grain.

The dyes of this invention are highly useful electron acceptors in high speed direct positive emulsions comprising fogged silver halide grains and a compound which accepts electrons, as described and claimed in Illingsworth U.S. patent application Ser. No. 609,794 filed Jan. 17, 1967, now abandoned and continuation-in-part 619,- 936, filed Mar. 2, 1967, and titled Photographic Reversal Materials III. The fogged silver halide grains of such emulsions are such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about one upon processing for six minutes at about 68 F. in Kodak DK-SO developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for six minutes at about 68 F. in Kodak DK-SO developer 4 after being bleached for about 10 minutes at about 68 F in a bleach composition of:

Water to 1 liter.

The grains of such emulsions will lose at least about and generally at least about of their fog when bleached for ten minutes at 68 F. in a potassium cyanide bleach composition as described herein. This fog loss can be illustrated by coating the silver halide grains as a photographic silver halide emulsion on a support to give a maximum density of at least 1.0 upon processing for six minutes at about 68 F. in Kodak DK-SO developer and comparing the density of such a coating with an identical coating which is processed for six minutes at 68 F. in Kodak DK- developer after being bleached for about 10 minutes at 68 F. in the potassium cyanide bleach composition. As already indicated, the maximum density of the unbleached coating will be at least 30% greater, generally at least greater, than the maxi mum density of the bleached coating.

The silver halides employed in the preparation of the photographic emulsions useful herein include any of the photographic silver halides as exemplified by silver bromide, silver iodide, silver chloride, silver chlorobromide, silver bromoiodide, and the like. Silver halide grains having an average grain size less than about one micron, preferably less than about 0.5 micron, gives particularly good results. The silver halide grains can be regular and can be any suitable shape such as cubic or octahedral, as described and claimed in Illingsworth US. patent application Ser. No. 609,778 filed Jan. 17, 1967 now abandoned, and continuation-in-part Ser. No. 619,909 filed Mar. 2, 1967, and titled Direct Positive Photographic Emulsions I. Such grains advantageously have a rather unrform diameter frequency distribution, as described and claimed in Illingsworth US. patent application Ser. No. 609,790 filed Jan. 17, 1967, now abandoned, and continuation-in-part Ser. No. 619,948 filed Mar. 2, 1967, and titled Photographic Reversal Emulsions II. For example, at least by weight, of the photographic silver halide grains can have a diameter which is within about 40%, preferably within about 30% of the mean grain diameter. Mean grain diameter, i.e., average grain size, can be determined using conventional methods, e.g., as shown in an article by Trivelli and Smith entitled Empirical Relations Between Sensitometric and Size-Frequency Characteristics in Photographic Emulsion Series in The Photographic Journal, vol. LXXIX, 1949, pages 330-338. The fogged silver halide grains in these directpositive photographic emulsions of this invention produce a density of at least 0.5 when developed without exposure for five minutes at 68 F. in Kodak DK-SO developer when such an emulsion is coated at a coverage of 50 to about 500 mg. of silver per square foot of support. The preferred photographic silver halide emulsions comprise at least 50 mole percent bromide, the most preferred emulsions being silver bromoiodide emulsions, particularly those containing less than about ten mole percent iodide. The photographic silver halides can be coated at silver coverages in the range of about 50 to about 500 milligrams of silver per square foot of support.

In the preparation of the above photographic emulsions, the dyes, reducing agents and metal compounds of the invention are advantageously incorporated in the washed, finished silver halide emulsion and should, of course, be uniformly distributed throughout the emulsion. The methods of incorporating dyes and other addenda in emulsions are relatively simple and well known to those skilled in the art of emulsion making. For example, it is convenient to add them from solutions in appropriate solvents, in which case the solvent selected should be completely free from any deleterious elfect on the ultimate light-sensitive materials. Methanol, isopropanol, pyridine, water, etc., alone or in admixtures, have proven satisfactory as solvents for this purpose. 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 satisfactory for dispersing silver halides, for example, emulsions comprising natural materials such as gelatin, albumin, agar-agar, gum arabic, alginic acid, etc., and hydrophilic synthetic resins such as polyvinyl alcohol, polyvinyl pyrrolidone, cellulose ethers, partially hydrolyzed cellulose acetate, and the like.

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. Particularly useful for direct positive fogged emulsions in which the silver salt is a silver bromohalide comprising more than 50 mole percent bromide. As indicated previously, certain dyes of this invention are also useful in emulsions which contain color formers. This is unexpected since related prior art dyes cannot be used in emulsions containing a color former.

The novel emulsions of this invention may be coated on any suitable photographic support, such as glass, film base such as cellulose acetate, cellulose acetate butyrate, polyesters such as polyethylene terephthalate, paper, baryta coated paper, polyolefin coated paper, e.g., polyethylene or polypropylene coated paper, which may be electron bombarded to promote emulsion adhesion, to produce the novel photographic elements of the invention.

Suitable unsymmetrical cyanine dyes for practicing our invention include those represented by the following general formula:

wherein n represents a positive integer of from 1 to 2, R represents a substituent selected from the group consisting of an alkyl radical, an aryl radical, an acyl radical and an organic sulfonyl radical, e.g., an alkyl substituent (including substituted alkyl) and preferably containing from about 1 to 8 carbon atoms, such as methyl, ethyl, propyl, butyl, octyl, sulfoalkyl such as sulfopropyl or sulfobutyl, sulfatoalkyl such as sulfatopropyl or sulfatobutyl, or carboxyalkyl such as carboxyethyl or carboxybutyl, or an aryl group, e.g., phenyl, sulfophenyl, carboxyphenyl, tolyl, etc., or an acyl group containing from about 1 to 10 carbon atoms, e.g., acetyl, propionyl, butyryl, benzoyl, etc., or an organic sulfonyl group from about 1 to 10 carbon atoms, e.g., an alkanesulfonyl group such as methanesulfonyl, ethanesulfonyl, butanesulfonyl, etc., or an aryl sulfonyl group such as benzenesulfonyl, etc., R represents an alkyl radical (including substituted alkyl) and preferably containing from about 1 to 10 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, octyl, decyl, sulfoalkyl such as sulfopropyl, sulfobutyl, etc., sulfatoalkyl such as sulfatopropyl, sulfatobutyl, etc., or carboxyalkyl such as carboxyethyl, carboxybutyl, etc., R and R ea ch represents H, an alkyl radical containing from 1 to 4 carbon atoms, e.g., methyl, ethyl, propyl, isopropyl, butyl, etc., or an aryl radical, e.g., phenyl, tolyl, chlorophenyl, methoxyphenyl, 3,4-dichlorophenyl, nitrophenyl, etc., or a carboxyl group, a sulfo group, a nitro group, a cyano group, or a halogen such as chlorine or bromine, X represents an acid anion, e.g., chloride, bromide, iodide, p-toluenesulfonate, thiocyanate, sulfamate, methyl sulfate, ethyl sulfate, perchlorate, etc., and Z represents the nonmetallic atoms required to complete a 5- to 6-membered heterocyclic nucleus, which nucleus may contain a second hetero atom such as oxygen, sulfur, selenium, or nitrogen, such as the following nuclei: a thiazole nucleus, e.g., thiazole, 4-methylthiazole, 4-phenylthiazole, S-methylthiazole, S-phenylthiazole, 4,5-dimethylthiazole, 4,5-diphenylthiazole, 4-(2- thienyl)thiazole, benzothiazole, 4-chlorobenzothiazole, 5- chlorobenzothiazole, 6-chlorobenzothiazole, 7-chlorobenzothiazole, 4-methylbenzothiazole, S-methylbenzothiazole, 6-methylbenzothiazole, S-bromobenzothiazole, 6- bromobenzothiazole, S-phenylbenzothiazole, S-phenylbenzothiazole, 4-methoxybenzothiazole, S-methoxybenzothiazole, 6-methoxybenzothiazole, 5-iodobenzothiazole, fi-iodobenzothiazole, 4-ethoxybenzothiazole, S-ethoxybenzothiazole, tetrahydrobenzothiazole, 5,6-dimethoxybenzothiazole, 5,6-dioxymethylenebenzothiazole, S-hydroxybenzothiazole, -hydroxybenzothiazole, a-naphthothiazole, B-naphthothiazole, 5-methoxy-,B,fl-naphthothiazole, S-ethoxy-fl-naphthothiazole, 8-methoxy-a-naphthothiazole, 7-methoxy-a-naphthothiazole, 4-methoxythianaphtheno-7,6,4,5-thiazole, etc.; an oxazole nucleus e.g., 4-methyloxazole, S-methyloxazole, 4-phenyloxazole, 4,5- diphenyloxazole, 4-ethyloxazole, 4,5-dimethyloxazole, 5- phenyloxazole, benzoxazole, 5 chlorobenzoxazole, 5- methylbenzoxazole, S-phenylbenzoxazole, 6-methylbenzoxazole, 5,6-dimethylbenzoxazole, 4,6-dimethylbenzoxazole, S-methoxybenzoxazole, S-ethoxybenzoxazole, 5- chlorobenzoxazole, 6-methoxybenzoxazole, S-hydroxybenzoxazole, 6-hydroxybenzoxazole, a-naphthoxazole, finaphthoxazole, etc.; a selenazole nucleus, e.g., 4-methylselenazole, 4-phenylselenazole, benzoselenazole, S-chlorobenzoselenazole, S-methoxybenzoselenazole, S-hydroxybenzoselenazole, tetrahydrobenzoselenazole, a-naphthoselenazole, ,B-naphthoselenazole, etc.; a thiazoline nucleus, e.g., thiazoline, 4-methylthiazoline, etc.; a pyridine nucleus, e.g., Z-pyridine, S-methyl-Z-pyridine, 4-pyridine, 3- methyl-4-pyridine, etc.; a quinoline nucleus, e.g., 2-quinoline, 3-methyl-2-quinoline, S-ethyl-Z-quinoline, 6-ch1oro- 2-quinoline, 8-chloro-2-quinoline, 6-methoxy-2-quinoline, 8-ethoxy-2-quinoline, 8-hydroxy-2-quinoline, 4-quinoline, 6-methoxy-4-quinoline, 7-methyl-4-quinoline, 8-chloro-4- quinoline, l-isoquinoline, 3,4-dihydro-l-isoquinoline, 3- isoquinoline, etc.; a 3,3-dialkylindolenine nucleus, preferably having a nitro or cyano substituent, e.g., 3,3-dimethyl-5 or 6-nitroindolenine, 3,3-dimethyl-5 or 6-cyanoindolenine, etc.; and, an imidazole nucleus, e.g., imidazole, l-alkylirnidazole, l-alkyl-4-phenylimidazo1e, 1-alkyl-4,5- dimethylimidazole, benzimidazole, l-alkylbenzimidazole, l-aryl-5,6-dichlorobenzimidazole, l-alkyl-a-naphthimidazole, 1-aryl-fi-naphthimidazole, 1-alkyl-5-methoxy-unaphthimidazole, and, 1,3-diethylimidazo[4,5-b1quinoxaline, etc. Dyes wherein Z represents the atoms required to complete an imidazo[4,5-b]quinoxaline nucleus are especially useful. A preferred class of dyes are those wherein Z represents the atoms necessary to complete a desensitizing nucleus. As used herein and in the appended claims, desensitizing nucleus refers to those nuclei which, when converted to a symmetrical carbocyanine dye and added to a gelatin silver chlorobromide emulsion containing 40 mole percent chloride and 60 mole percent bromide, at a concentration of from 0.01 to 0.2 gram dye per mole of silver, cause by electron trapping at least about an percent loss in the blue speed of the emulsion when sensitometrically exposed and developed three minutes in Kodak developer D-l9 at room temperature. Advantageously, the desensitizing nuclei are those which, when converted to a symmetrical carbocyanine dye and tested as just described, essentially completely desensitize the test emulsion to blue radiation (i.e., cause a loss of more than about to loss of speed to blue radiation).

The above defined unsymmetrical cyanine dyes of the invention can be conveniently prepared by condensing the appropriate carbazole-3-carboxaldehyde, preferably having the general formula:

CHO R l III.

wherein n, R X and Z are as previously defined, in an inert dehydrating medium such as, for example, acetic anhydride, at elevated temperatures and preferably at refluxing temperatures of the reaction mixtures. On chilling, the dye compounds separate from the mixture and are purified by one or more recrystallizations from suitable solvents such as an alkanol alone or in admixture with a phenol, for example, from methanol or mixture of methanol and cresol. The reactants can be employed with a small excess of one or the other, i.e., greater than the stoichiometrically calculated equivalents, but preferably in the approximately equimolar proportions for the best results. Intermediate carbazole-B-aldehyde represented by Formula II above can be prepared as described in The Chemistry of Heterocyclic Compounds With Indole and Carbazole Systems, Chapter II, W. C. Sumpter and F. M. Miller, Interscience Publishers, Inc., New York 1954. The intermediate heterocyclic compounds represented by Formula III above are all known substances, and methods for preparing these compounds are well known to the art. The invention is further illustrated by the following examples. Example 1.1,3-diethyl-2-p-(9-methyl-3 carbazoly1)vinylimidazo 4,5-b] -quinoxalinium iodide I N CE=CHO/ T 9-methylcarbazole-3-carboxaldehyde (1.05 g. 1 mol.) and 1,3-diethyl 2 methylimidazo[4,5-b] quinoxalinium iodide (1.85 g. 1 mol.) in acetic anhydride (10 ml.) are refluxed for 5 minutes, during which time some solid separated. The mixture is transferred to a beaker with the aid of a little acetic acid and chilled. The solid is collected and Washed with ether. After two recrystallizations from methanol, the yield of purified dye is 0.48., (17%), M.P. 270-3 C. dec.

A gelatin silver bromoiodide emulsion (2.5 mole percent of the halide being iodide) and having an average grain size of about 0.2 micron is prepared by adding an aqueous solution of potassium bromide and potassiume iodide, and an aqueous solution of silver nitrate, simultaneously to a rapidly agitated aqueous gelatin solution at a temperature of 70 C. over a period of about minutes. The emulsion is chill-set, shredded and washed by leaching with cold water in the conventional manner. The emulsion is reduction-gold fogged by first adding 0.2 mg. of thiourea dioxide per mole of silver and heating for 60 minutes at 65 C. and then adding 4.0 mg. of potassium chloroaurate per mole of silver and heating for 60 minutes at 65 C. The above prepared dye, 1,3-diethyl-2-B-(9-methyl-3-carbazolyl)vinylimidazo[4,4-b]quinoxalinium iodide is then added to the above fogged emulsion in amount sufiicient to give a concentration of 0.176 gram of the dye per mole 4 of silver. The resulting emulsion is then coated on a cellulose acetate film support at a coverage of 100 mg. of silver and 400 mg. of gelatin per square foot of support.

A sample of the coated support is then exposed on an Eastman Ib sensitometer using a tungsten light source and processed for 6 minutes at room temperature in Kodak D-19 developer which has the following composition:

G. N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite (anhydrous) 90.0 Hydroquinone 8.0 Sodium carbonate (monohydrate) 52.5 Potassium bromide 5.0

Water to make 1.0 liter.

then fixed, washed and dried. The results are listed in Table I hereinafter. Referring thereto, it will be seen that the dye of this example has a minimum density in exposed areas of only 0.05, a sensitivity range up to 650 m and a maximum sensitivity at 575 m Whereas the control sample similarly prepared and tested but containing no spectral sensitizing dye increases in density with expo sure. This result indicates that the dye compound of the above example is especially well suited to function as both an electron acceptor and spectral sensitizer. It thus provides excellent quality direct positive photographic silver halide emulsions. Excellent magenta images are obtained when the color former 1-(2,4,6-trichlorophenyl)-3,3'-(2", 4-di-t-amylphenoxyacetamido)benzimidazo 5 pyrazolone is incorporated in the emulsion of this example, the emulsion is coated on a support, exposed to a tungsten source through Wratten filter No. 61 and No. 16, and reversal processed as described in Graham et al. US. Patent 3,046,129, issued July 24, 1962, in Example (a), col. 27, lines 27 et seq. except that black-and-white (MQ) development is omitted, the color development is reduced to one minute and is conducted in total darkness until after fixing.

Example 2.3-methyl-2-,B-(9-methyl-3-carbazolyl)vinyl- 6-nitro-benzothiazoliump-toluenesulfonate 9-methylcarbazole-3-carboxaldehyde (1.05 g., 1 mol.) and 2,3-dirnethyl 6 nitrobenzothiazolium p toluenesulfonate (1.90 g., 1 mol.) in acetic anhydride (25 ml.) are refluxed for five minutes, during which time much dye separates. The mixture is transferred to a beaker with the aid of a little acetic acid and cooled. The solid is collected and washed with ether. After two recrystallizations from cresol/methanol, the yield of purified dye is 1.67 g. (59%), M.P. 300. In the above formula, pts stands for the p-toluene sulfonate radical.

The above prepared dye compound is photographically tested by the exact procedure of Example I. Referring to Table I, it will be seen that the dye of this example has a minimum density in the exposed areas of only 0.04, a sensitivity range up to 630 Ill/L, and a maximum sensitivity at 550 my, whereas the control sample similarly prepared and tested, but containing no spectral sensitizing dye, increases in density with exposure. Accordingly, the dye of this example provides especially useful direct positive materials.

Example 3.5-chloro-3-methyl-2-B-(9-methylcarbazolyl) vinyl-6-nitrobenzothiazolium p-toluenesulfonate N02 CH=CHC\\ 01 N (I: C pts 9-methylcarbazole-carboxaldehyde (1.05 g., 1 mol) and 5 chloro-Z,3-dimethyl-6-nitrobenzothiazolium p-toluenesulfonate (2.08 g., 1 mol) in acetic anhydride (20 ml.) are refluxed for 5 minutes, as much dye separated. The cooled mixture is diluted with ether and the solid collected and washed with ether. After two recrystallizations from cresol/methanol, the yield of purified dye is 1.40 g. (46%), M.P. 297 C. dec.

The above prepared dye compound is photographically tested by the exact procedure of Example 1. The results as shown in Table I indicate that the dye of this example provides excellent direct positive materials.

taining an equivalent of grams of silver nitrate is added 0.017 gram of 1,3 diethyl 2 ,B-(9-methyl-3-carbazolyl)vinylimidazo [4,5-b] quinoxalinium iodide. The emulsion is coated on a non-glossy paper support, and is flashed with white light to give a density of 1.2 when developed in the following developer, diluted 1 part to 2 parts of water:

Grams N-methyl-p-aminophenol sulfate 3.1 Sodium sulfite, des 45 Hydroquinone 12 Sodium carbonate, des 67.5 Potassium bromide 1.9

Water to 1 liter.

Seven pounds of a silver chloride gelatin emulsion containing the equivalent of 100 g. of silver nitrate is heated to 40 C. and the pH is adjusted to 7.8. Eight cc. of full strength (40%) Formalin solution is added and the emulsion is held at 40 C. for minutes. At the end of the holding period, the pH is adjusted to 6.0 and 0.125 g. of 3 methyl- 2 p (9-methyl-3-carbazolyl)vinyl-6-nitrobenzothiazolium p toluenesulfonate. The emulsion is coated on a support, and provides good direct positive images. Similar results are obtained when the dye of Example 1 is substituted for 3-methyl-2-j3-(9-methyl-3- carbazolyl)vinyl 6 nitrobenzothiazolium p toluenesulfonate.

By substituting other dye compounds of the invention, as defined in Formula I above, into the procedure of the above examples generally similar fogged, direct positive photographic silver halide emulsions and photographic elements may be prepared. For example, eifective dye compounds of the invention include 3-methyl-2-fl-(9-methyl-7-nitro-3-carbazolyl)vinyl-S- chlorobenzothiazolium p-toluenesulfonate, 3-ethyl-2-fl-(9-ethyl-3-carbazolyl)vinyl-6-nitrobenzothiazolium p-toluenesulfate, 3-butyl-2-B-(9-butyl-3-carbazolyl)vinyl-6-chlorobenzothiazolium perchlorate, 3-methyl-2-p-(9-methyl-3-carbazolyl)vinyl-6-nitrobenzoxazolium p-toluenesulfonate, 3-ethyl-2- 3-(9-ethyl-3-carbazolyl)vinyl-S-chlorobenzoxazolium p-toluenesulfonate, 1,3,3-trimethyl-2-B-(9-methyl-3-carbazolyl)vinyl-S-nitro- 3H-indolium perchlorate, and the like.

The photographic silver halide emulsion and other layers present in the photographic elements made according to the invention can be hardened with any suitable hardener, including aldehyde hardeners such as formaldehyde, and mucochloric acid, aziridine hardeners, hardeners which are derivatives of dioxane, oxypolysaccharides such as oxy starch or my plant gums, and the like. The emulsion layers can also contain additional additives, particularly those known to be beneficial in photographic emulsions, including, for example, lubricating materials, stabilizers, speed increasing materials, absorbing dyes, plasticizers, and the like. These photographic emulsions can also contain in some cases additional spectral sensitizing dyes. Furthermore, these emulsions can contain color forming couplers or can be developed in solutions containing couplers or other color generating materials. Among the useful color formers are the monomeric and polymeric color formers, e.g. pyrazolone color formers, as well as phenolic, heterocyclic and open chain couplers having a reactive methylene group. The color forming couplers can be incorporated into the direct positive photographic silver halide emulsion using any suitable technique, e.g., techniques of the type shown in Ielley et al. US. Patent 2,322,027, issued Jan. 15, 1943, Fierke et al. US. Patent 2,801,171, issued July 30, 1957, Fisher 10' US. Patents 1,055,155 and 1,102,028, issued Mar. 4, 1913 and June 30, 1914, respectively, and Wilmanns US. Patent 2,186,849 issued Jan. 9, 1940. They can also be developed using incorporated developers such as polyhydroxybenzenes, aminophenols, 3-pyrazolidones, and the like.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, it will be understood that the variations and modifications can be efiected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

We claim:

1. A foggcd direct positive photographic silver halide emulsion containing at least one unsymmetrical cyanine dye compound selected from those represented by the following general formula:

oH=oH- (=CH-CH) =1 IR l; I l

wherein n represents a positive integer of from 1 to 2, R represents a substituent selected from the group consisting of an alkyl radical, an aryl radical, an acyl radical and an organic sulfonyl radical; R represents an alkyl radical; R and R each represents a member selected from the group consisting of hydrogen, an alkyl radical, an aryl radical, a carboxyl group, a sulfo group, a nitro group, a cyano group and a halogen atom, X represents an acid anion, and Z represents the nonmetallic atoms required to complete a 5- to 6-membered heterocyclic nucleus.

2. A direct positive photographic silver halide emulsion in accordance with claim 1 wherein Z represents the atoms necessary to complete a nucleus selected from the class consisting of a thiazole nucleus, an oxazole nucleus, a selenazole nucleus, a thiazoline nucleus, a pyridine nucleus, a quinoline nucleus and an imidazole nucleus; and, R represents a member selected from the group consisting of an alkyl group, an aryl group, an acyl group, and an alkane-sulfonyl group and an arylsulfonyl group.

3. A direct positive emulsion in accordance with claim 1 wherein Z represents the atoms required to complete a desensitizing nucleus.

4. A direct positive emulsion in accordance with claim 2 wherein Z represents the atoms required to complete a desensitizing nucleus.

5. A direct positive photographic emulsion of claim 1 in which the said silver halide is present in the form of light fogged silver halide grains.

6. A direct positive photographic emulsion of claim 1 in which the said silver halide is present in the form of chemically fogged silver halide grains.

7. A direct positive photographic emulsion of claim 6 containing the dye compound l,3-diethyl-2-fi-(9methyl- 3-carbazolyl) vinylimidazo [4,5 -b] quinoxalinium iodide.

'8. A direct positive photographic emulsion of claim 6 containing the dye compound 3-methyl-2-fl-(9-methyl-3- carbazolyl)vinyl 6 nitrobenzothiazolium p-toluenesulfonate.

9. A direct positive photographic emulsion of claim 6 containing the dye compound 5-chloro-3-methyl-2-B- (9-methyl-3-carbazolyl)vinyl 6 nitrobenzothiazolium ptoluenesulfonate.

10. A direct positive photographic emulsion of claim 6 containing the dye compound 1,3,3-trimethyl-2-fl-(9- methyl-B-carbazolyl)vinyl 5 nitro-SH-indolium perchlorate.

11. A direct positive photographic emulsion of claim 6 containing the dye compound 3-methyl-2-fl-(9-methyl- 3 carbazolyl)vinyl-6-nitrobenzoxazolium p-toluenesulfonate.

12. A photographic element comprising a support coated with at least one layer containing a direct positive photographic silver halide emulsion of claim 1.

13. A photographic element comprising a support coated with at least one layer containing a direct positive photographic silver halide emulsion of claim 6.

14. A direct positive emulsion in accordance with claim 1 containing a photographic color former.

15. A direct positive, photographic emulsion in accordance with claim 1 which comprises fogged silver halide grains, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68 F. in Kodak DK-SO developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak DK50 developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

Potassium cyanide mg 50 Acetic acid (glacial) cc 3.47 Sodium acetate g 11.49 Potassium bromide mg 119- Water to 1 liter.

16. A direct positive, photographic emulsion in accordance with claim 1 which comprises fogged silver halide grains, at least 95%, by weight, of said grains having a size which is within about 40% of the average grain.

17. A direct positive, photographic emulsion in accordance with claim 2 which comprises fogged silver halide grains, said grains being such that a test portion thereof,

when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68 F. in Kodak DK-SO developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak DK- developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

Potassium cyanide mg 50 Acetic acid (glacial) cc 3.47 Sodium acetate g 11.49 Potassium bromide mg 119 Water to 1 liter.

18. A direct positive, photographic emulsion in accordance with claim 2 which comprises fogged silver halide grains, at least by weight, of said grains having a size which is within about 40% of the average grain.

References Cited UNITED STATES PATENTS 6/1967 Jenkins 96-102 FOREIGN PATENTS 760,739 11/ 1956 Great Britain.

NORMAN G. TORCHIN, Primary Examiner RICHARD E. FICHTER, Assistant Examiner US. (:1. X.R. 96--101, 107