US3579346A - Silver halide emulsions with dyes containing a pyrylium nucleus joined to a pyrazole nucleus - Google Patents

Abstract

NOVEL PHOTOGRAPHIC METHINE DYES ARE PROVIDED WHICH FEATURE A PYRYLIUM NUCLEUS JOINED, BY A METHINE CHAIN, TO A PYRAZOLE NUCLEUS OR A NITRO SUBSTITUTED NUCLEUS OF THE TYPE USED IN CYANINE DYES. LIGHT SENSITIVE SILVER HALIDE EMULSIONS ARE ALSO PROVIDED COMPRISING THE NOVEL DYES OF THIS INVENTION.

Description

United States Patent ()ffice 3,579,346 SILVER HALIDE EMULSIONS WITH DYES CON- TAINING A PYRYLIUM NUCLEUS JOINED TO A PYRAZOLE NUCLEUS Leslie G. S. Brooker, Donald W. Heseltine, and Daniel S. Daniel, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y. No Drawing. Filed Mar. 25, 1968, Ser. No. 715,530 Int. Cl. G03c 1/10; C09b 23/10 US. Cl. 96-406 32 Claims ABSTRACT OF THE DISCLOSURE Novel photographic methine dyes are provided which feature a pyrylium nucleus joined, by a methine chain, to a pyrazole nucleus or a nitro substituted nucleus of the type used in cyanine dyes. Light sensitive silver halide emulsions are also provided comprising the novel dyes of this invention.

This invention relates to novel photographic materials, and more particularly to a new class of dyes. It also relates to light-sensitive silver halide emulsions containing these dyes. The dyes of this invention are especially useful as electron acceptors and spectral sensitizers for direct positive photographic silver halide emulsions.

It is known that direct positive images can be obtained with certain types of photographic silver halide emulsions. For example, photographic emulsions have been proposed for this purpose comprising an electron acceptor and silver halide grains that have been fogged with a combination of a reducing agent and a compound of a metal more electropositive than silver. One of the advantages of such direct positive emulsions is that the high-light areas of the images obtained with these materials are substantially free from fog. However, known materials of this type, for example, British Pat. 723,019, have not exhibited the high speed required for many applications of photography. Also, such known materials have not shown the desired selective sensitivity, especially to radiation in the green to red region of the spectrum. It is evident, therefore, that there is need in the art for improved direct positive photographic materials having both good speed and desirable sensitivity to longer wavelength radiations.

It is, accordingly, an object of this invention to provide new and improved direct positive photographic silver halide emulsions, and more particularly, fogged emulsions of this type, containing one or more of the polymethine dyes of the invention. 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 direct positive photographic emulsions of this invention. Other objects will become apparent from this disclosure and the appended claims.

We have now found certain novel dyes which 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 spectrum with maximum sensitivity occurring in most cases in the region of about 530-650 nm. The images produced with these new direct positive emulsions are clear and sharp.

The new class of methine dyes of the invention include those comprising first and second heterocyclic nuclei joined together by a methine linkage containing from 1 to 3 carbon atoms in the chain, e.g., monomethine, dimethine and trimethine linkages; the first of said nuclei being a pyrylium or a thiapyrylium nucleus, and the second nucleus being: (a) a 5 to 6 membered nitrogen contain- 3,579,346 Patented May 18, 1971 ing heterocyclic nucleus of the type used in cyanine dyes, said nucleus containing a nitro group and being joined to the methine linkage at a carbon atom thereof; or, (b) a pyrazole nucleus, joined at the 4-carbon atom thereof to the methine linkage. As used herein and in the appended claims, the terms pyrylium and thiapyrylium are used broadly to include oxonium and thioniurn salts which have an aromatic system and contain six atoms in the heterocyclic ring (which ring may have one or more rings or nuclei fused thereto). The pyrylium or thiapyrylium nucleus is preferably joined at a carbon atom thereof, which is ortho or para to the heterooxygen or sulfur atom, to the methine linkage. Typical useful pyrylium and thiapyrylium nuclei include pyrylium; benzopyrylium; naphthopyrylium; thiapyrylium; benzothiapyrylium; naphthothiapyrylium; a 6,7-dihydro-5H-cyclopenta [b] pyrylium nucleus; a 6,7 dihydro 5H-cyclopenta[b]thiapyrylium nucleus; a 5,6,7,8 tetrahydrocyclohexa[b]pyrylium nucleus; a 5,6,7,8 tetrahydrocyclohexa[bJthiapyrylium nucleus, an 8,9,10,11 tetrahydrobenzo[a]xanthylium nucleus; and, an 8,9,10,ll-tetrahydrobenzo[a] thiaxanthylium nucleus.

Typical useful dyes of the invention include those represented by the following general formulas:

I Ilig Rs rule, A X

and the other of A and A represents a hydrogen atom, an alkyl group (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, decyl, etc., or an aryl group, e.g., phenyl, tolyl, naphthyl, chlorophenyl, ethoxyphenyl, nitrophenyl, etc.; n and m each represents a positive integer of from 1 to 2; R represents an alkyl group, including substituted alkyl (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., and substituted alkyl groups (preferably a substituted lower alkyl containing from 1 to 4 carbon atoms), such as a hydroxyalkyl group, e.g., B-hydroxyethyl, w-hydroxybutyl, etc., an alkoxyalkyl group, e.g., fi-methoxyethyl, w-but0xybutyl,

etc., a carboxyalkyl group, e.g., fl-carboxyethyl, w-carboxybutyl, etc., a sulfoalkyl group, e.g., fi-sulfoethyl, w-sulfobutyl, etc., a sulfatoalkyl group, e.g., B-sulfatoethyl, wsulfatobutyl, etc., an acyloxyalkyl group, e.g., B-acetoxyethyl, 'y-acetoxypropyl, w-butyryloxybutyl, etc., an alkoxycarbonylalkyl group, e.g., fi-methoxycarbonylethyl, wethoxycarbonylbutyl, etc., an aralkyl group, e.g., benzyl, phenethyl, etc.; or any aryl group, e.g., phenyl, tolyl, naphthyl, methoxyphenyl, chlorophenyl, etc.; R through R each individually represents a hydrogen atom, an alkyl group (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, decyl, etc., or an aryl group, e.g., phenyl, tolyl, naphthyl, chlorophenyl, ethoxyphenyl, nitrophenyl, etc.; R and R taken together represent the atoms required to complete a fused phenyl or naphthyl ring; D represents oxygen or sulfur; X represents an acid anion, e.g., chloride, bromide, iodide, sulfamate, perchlorate, p-toluenesulfonate, methyl sulfate, etc.; Q represents an ethylene or trimethylene bridge group; and, Z represents the non-metallic atoms necessary to complete a desensitizing nitro group substituted heterocyclic nucleus of the type used in cyanine dyes which contains from 5 to 6 atoms in the ring including: a nitrobenzothiazole nucleus, e.g., S-nitrobenzothiazole, 6 nitrobenzothiazole, 5 chloro 6-nitrobenzothiazole, etc.; a nitrobenzoxazole nucleus, e.g., 5-nitrobenzoxazole. 6-nitrobenzoxazole. 5-chloro-6-nitrobenzoxazole. etc.; a nitrobenzoselenazole nucleus, e.g., S-nit obenzoselenazole, N-nitrobenzoselenazole, 5-chloro-6-nitrobenzoselenazole, a nitroindolenine nucleus, e.g., 1,3,3-trimethyl-S-nitroindolenine, etc.; a nitropyridine nucleus, e.g., S-nitropyridine, etc.; a nitroquinoline nucleus, e.g., 6- nitroquinoline, etc.; and the like.

The dyes of the invention defined above are powerful electron acceptors and spectral sensitizers for direct positive photographic silver halide emulsions. In addition, they are also useful desensitizers in emulsions used in the process described in Stewart and Reeves, US. Pat. No. 3,250,618, issued May 10, 1966.

As used herein desensitizing nucleus refers to those nuclei which, when converted to a symmetrical carbocyanine dye and added to 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 80 percent loss in the blue speed of the emulsion when sensitometrically exposed and developed three minutes in Kodak developer D19 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 more than about 90 to 95 percent loss of speed to blue radiation).

The dyes defined by Formula I above are conveniently prepared for example, by heating a mixture of 1) a compound of the formula:

wherein R through R D, X and Q are as previously defined, in approximately equimolar proportions, in a solvent medium such as acetic anhydride. Dyes having Formula Ia. can be prepared in a similar manner, by reacting a compound of Formula III above with a compound of Formulas VI or VIa below. The crude dye is then separated from the reaction mixture, washed, and purified by one or more recrystallizations from appropriate solvents such as acetonitrile, mixtures of methanol and acetic acid, etc.

The dyes of Formula II(b) above are advantageously prepared, for example, by heating a mixture of (1) a compound of the formula:

and (2) a compound of Formula IV above, wherein R R D and X are as previously defined; and at least one of B and B represents a methyl group and the other of said B and B represents a hydrogen atom or an alkyl group or an aryl group, e.g., methyl, butyl, decyl, phenyl, tolyl, naphthyl, chlorophenyl, ethoxyphenyl, nitrophenyl, etc., in approximately equimolar proportions in a solvent medium such as acetic anhydride. The crude dye is separated from the reaction mixture and purified by one or more recrystallizations from appropriate solvents such as a mixture of methanol and acetic acid.

To prepare the dyes of Formula II(a) above, a mixture comprising (1) a compound of Formula V above and (2) a compound having one of the formulas:

VI I --z VIa. ;Z- R1I I =oH oH)..-1=o'W or R1I\'I =oncno I i (CH C1'I)n1 wherein n, R X and Z are as previously defined, and W represents the group SR (for the dyes where m is 1) wherein R represents an alkyl or aryl group, e.g., methyl, phenyl, etc., or the group CH=CHN(COCH )C H (for dyes where m is 2), is reacted under reflux in a suitable solvent, and in approximately equimolar proportions, the pure dye being obtained in the general manner previously described.

In accordance with the invention, novel and improved photographic silver halide emulsions are prepared by incorporating one or more of the cyanine dyes of the invention therein. The emulsion can be a direct positive emulsion, such as a 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 Pat. 723,019 (1955).

Typical reducing agents that are useful in proving such emulsions include stannous salts, e.g., stannous chloride, hydrazine, sulfur compounds such as thiourea dioxide, phosphonium salts such as tetra(hydroxymethyl) phosphonium chloride, and the like. Typical useful metal 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 (NHQ PdCI 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 minutes at 68 F. in developer Kodak DK-50 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 Hydroquinone 2.5 Sodium metaborate 10.0

Potassium bromide 0.5

Water to make 1.0 1.

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 waterinsoluble 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. Pat. 3,367,778, issued Feb. 6, 1968. 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 fog is removable by bleaching. The shell is of sufiicient 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 100 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 core 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.

DEVELOPER A G. N-methyl-paminophenol 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 emulsions are 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. XXVVIII, 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. 619,936, filed Mar. 2, 1967, now U.S. Pat. 3,501,307, issued Mar. 17, 1970. 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-50 developer, has a maximum density which is at least about 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 after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

potassium cyanide50 mg. acetic acid (glacial)3.47 cc.

. sodium acetate1l.49 g.

potassium bromide1 19 mg. water to 1 liter The grains of such emulsions will lose at least about 25% and generally at least about 40% 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-SO 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 60% greater, than the maximum 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, silver chlorobromide, and the like. Silver halide grains having an average grain size less than about one micron, preferably less than about 0.5 micron, give 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 U.S. patent application Ser. No. 619,909, filed Mar. 2, 1967, now U.S. Pat. 3,501,306, issued Mar. 17, 1970. Such grains advantageously have a rather uniform diameter frequency distribution, as described and claimed in Illingsworth U.S. patent application Ser. No. 619,948, filed Mar. 2, 1967, now U.S. Pat. 3,501,305, issued Mar. 17, 1970. 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 direct positive 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,

7 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 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 dye 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 effect on the ultimate light-sensitive materials. Methanol, isopropanol, pyridine, water, etc., alone or in admixture, 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, polyvinylpyrrolidone, cellulose ethers, partially hydrolyzed cellulose acetate, and the like.

The binding agents for the emulsion layer of the photographic element can also contain dispersed polymerized vinyl compounds. Such compounds are disclosed, for example, in U.S. Pats. 3,142,568; 3,193,386; 3,062,674; and 3,220,844 and include the water-insoluble polymers of alkayl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates, 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. Certain dyes of this invention are also useful in emulsions which contain color formers.

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.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 2-[2-(3,S-dimethyl-1-phenyl-4-pyrazolyl)vinyl] -4,6- di-(4-ethoxyphenyl)-pyrylium fiuoroborate A mixture of 1.46 g. (1 mol.) of 4,6-di-(4-ethoxyphenyl)-2-methylpyrylium fiuoroborate, 0.7 g. (1 mol.) of 3,5-dimethyl-1-phenyl-4-pyrazole aldehyde and acetic anhydride ml.) is heated under reflux for 10 minutes. The mixture is allowed to cool and ether is then added to precipitate the dye product. The crude dye is collected on a filter and washed several times with ether. After two recrystallizations from a mixture of methanol and acetic acid, the yield of pure dye crystals is 0.54 g. (27% M.P. 238-239" C.

The above prepared dye containing the desensitizing 3,S-dimethyl-l-phenylpyrazole nucleus is photographically tested for its usefulness as an electron acceptor and spectral sensitizer for fogged direct positive photographic silver halide emulsions by the following procedure.

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 potassium iodide, and an aqueous solution of silver nitrate, simultaneously to a rapidly agitated aqueous gelatin tolusion at a temperature of 70 C., over a period of about 35 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 dye of the above example is then added to the above fogged emulsion in an amount sufficient to .give a concentration of 0.20 gram of the dye per mole of silver. The resulting emulsion is coated on a cellulose acetate film support at a coverage of 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:

N-methyl-n-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 maximum density in the unexposed areas of 1.80 and a minimum density in exposed areas of 0.28, a maximum sensitivity of 550 nm. and a relative speed of 347. It will be noted that the control containing no dye has a relative speed of 1 and shows no reversal. This result indicates that the dye compound of the above example is 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 l-(2,4,6-trichlorophenyl)-3,3'-(2",4"-dit-amylphenoxyacetamido -benzimidazo-S-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. U.S. Pat. 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.

In place of the 4,6-di-(4-ethoxyphenyl)-2-methyl-pyrylium fiuoroborate or the 3,S-dimethyl-l-phenyl-4-pyrazole aldehyde in Example 2, there can be substituted an equivalent amount of any other of the related intermediates defined by Formula III or IV above to give other dyes embraced by Formula I above having generally similar properties as electron acceptors and spectral sensitizers for direct positive silver halide emulsions, for example, dyes such as 2 [2-(3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl]- 4,6 di (4-ethoxyphenyl)thiapyrylium salt, e.g., fluoroborate; 2-[2-(3,5-dimcthyl-l-phenyl 4 pyrazolyl)vinyl]- 4,6 diphenylpyrylium salt, e.g., perchlorate; 2-[2-(3,5- dimethyl 1 phenyl-4-pyrazolyl)vinyl]-4,6-diethylpyrylium salt, e.g., perchlorate; 4-[2-( 3,5 dimethyl-l-phenyl-4- pyrazolyl)vinyl] 2 phenyl-l-benzopyrylium salt, e.g., perchlorate; 2 [2 (l phenyl 4 pyrazolyl)vinyl]-4- phenylpyrylium salt; 4-[2-( 1,3,5-trimethyl 4 pyrazolyl) 9 vinyl] 2 phenyl-l-benzopyrylium salt and the like dyes. Dyes having Formula Ia above can be prepared by reacting an intermediate having Formula III above, such as 7-ethoxymethylene 6,7 dihydro-2,4-diphenyl-H-cyclopenta[b]py-ry-lium salt, (e.g. perchlorate) with a suitable intermediate, such as 3-ethyl-2-methyl 6 nitrobenzothiazoliurn salt (e.g., p-toluenesulfonate) or 1,2,3,3-tetramethyl-S-nitroindoliniurn salt, (e.g. perchlorate), to obtain the dye 3-ethyl-3,7-ethylene-6'-n.itro-4,6-diphenyl-2- pyrylo-thiacarbocyanine salt (e.g., perchlorate), 1,3,3-trimethyl-3',10-trirnethylene 5 nitro-4',6-diphenylindo- 2-pyrylocarbocyanine salt (e.g., perchlorate), 3,7-ethylene-3'-methyl-6-nitro 4,6 diphenyl-4,5'-benzopyrylocarbocyanine salt, (eg perchlorate) and 3-methyl-3',10-

vtrimethylene 5 nitro-4',-6'-diphenyl-oxa-2'pyrylocarbocyanine salt (e.g., perchlorate).

EXAMPLE 2 8-[(3,5 dimethyl-l-phenyl 4 pyrazoly1)methylene]- 8,9, 1 0,1 l-tetrahydrobenzo a] xanthylium perchlorate A mixture of 0.84 g. -(1 mol.) of 8,9,10,11-tetrahydrobenzo[a]xanthylium perchlorate, 0.60 g. of 3,5-dimethyl- 1-phenyl-4-pyrazole aldehyde and acetic anhydride (10 ml.) is heated under reflux for 10 minutes. The mixture is allowed to cool, and the dye crystals are filtered out, washed with ethyl acetate and ethanol. The yield of pure dye obtained by recrystallization from acetonitrile is 0 .32 g. (25%), MP. 223-224 C.

The above prepared dye is photographically tested by the exact procedure described in above Example 1. The results are recorded in Table I hereinafter. Referring to the table, the densities are 1.32 and 0.16 for the unexposed and exposed areas, respectively, with maximum sensitivity 600 nm. and a relative speed of 501. In contrast, the control containing no dye has a relative speed 1 and shows no reversal. Accordingly, the above dye is an excellent electron acceptor and spectral sensitizer for fogged direct positive photographic silver halide emulsions.

It will be apparent that the 3,5-dimethyl-1-phenyl-4- pyrazole aldehyde in the above Example 2 can be replaced with an equivalent amount of any other of the intermediates defined by Formula V above to give related dyes having generally similar properties as electron acceptors and spectral sensitizers for direct positive silver halide emulsions, for example, dyes such as 8-[(1,3,5-triphenyl-4- pyrazolyl)methylene] 8,9,10,11 tetrahydrobenzo[a] xanthylium salts (e.g., the bromide, perchlorate, p-toluenesulfonate, fluoroborate, etc. salt); and the like dyes.

Also, the 8,9,10,1l-tetrahydrobenzo[a]xanthylium perchlorate in the above Example 2 can be replaced with the corresponding thiaxanthylium salt to give the corresponding dye compound, for example, the 8-[(3,5-dimethyl-1- phenyl 4 pyrazolyDmethylene] 8,9,10,11-tetrahydrobenzo [a] thiaxanthylium salt (e.g., the bromide, perchlorate, p-toluenesulfonate, fluoroborate, etc. salt); and the like dyes.

10 EXAMPLE 3 CaHa A mixture of 1.60 g. (1 mol.) of 4-methyl-2-phenyl-1- benzopyrylium perchlorate, 2.38 g. of 3-methyl-6-nitro- 2-phenylthiobenzothiazolium p-toluenesulfonate, acetonitrile (20 ml.) and acetic anhydride (20 ml.) is heated under reflux for 10 minutes. The mixture is allowed to cool, and the dye crystals are filtered out and washed with ethanol. The yield of pure dye obtained by recrystallization from a mixtire of m-cresol and ethanol is 0.86 g. (65%), MP. 300 C.

The above prepared dye containing the desensitizing nitrobenzothiazole nucleus is photographically tested by the exact procedure described in above Example 1. The results are recorded in Table I hereinafter. Referring thereto, it will be noted that the densities are 1.96 and .07 for the unexposed and exposed areas, respectively, with maximum sensitivity at 566 nm., and a relative speed of 479. The control containing no dye has a relative speed of 1 and shows no reversal. The above dye is, accordingly, an excellent electron acceptor and spectral sensitizer for fogged direct positive photographic emulsions.

In place of the 3-methyl-6-nitro-2-phenylthiobenzothiazolium p-toluenesulfonate in above Example 3, there can be substituted an equivalent amount of any other of the intermediates defined by Formula VI above to give the corresponding related dye embraced by Formula H above having generally similar properties as electron acceptors and spectral sensitizers for direct positive silver halide emulsions, for example, dyes such as 3-methyl-6'-nitro-2- phenyl-4-(1 benzopyrylo) 2 oxacyanine salt (e.g., the bromide, perchlorate, p-toluenesulfonate, fluoroborate, etc. salt); 3'-methyl-6nitro-2-phenyl-4-(1-benzopyrylo)- 2'-selenacarbocyanine salt (e.g., the bromide, perchlorate, p-toluensulfonate, fluoroborate, etc. salt); and the like dyes.

Also, in place of the 4-methyl-2-phenyl-l-benzopyrylium perchlorate in above Example 3, there can be substituted other related intermediates defined by Formula V above to give still other dyes embraced by Formula II above having generally similar properties as electron acceptors and spectral sensitizers for direct positive silver halide emulsions, for example, dyes such as 3'-methyl-6- nitro-2-phenyl-4-(1 benzothiapyrylo)-2-thiacyanine salt (e.g., the bromide, perchlorate, p-toluenesulfonate, fluoroborate, etc. salt); 3-ethyl-6'-nitr0-4,6-diphenyl-2-pyrylo- 2'-thiacyanine salt (e.g., the bromide, perchlorate, p-toluensulfonate, fluoroborate, etc. salt); and the like dyes.

The efl ectiveness of the dyes of the invention as electron acceptors and spectral sensitizers as determined by the testing procedure described in above Example 1, is recorded in the following Table I.

The following examples further illustrate the preparation of fogged, direct positive photographic emulsions and elements with the cyanine dyes of the invention.

1 1 EXAMPLE 4 G. 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.

The light fogged material can be exposed to an image with light modulated by a Wratten No. 15 filter to give a direct positive image. Generally, similar results are obtained when the dyes of Examples 2 and 3 are used in place of the above dye.

EXAMPLE 5 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 the dye of Example 3 is added. The emulsion is coated on a support, and provides good direct positive images. Generally similar results are obtained when the dyes of Examples 1 and 2 are substituted for the above dye.

It was highly surprising to find that the dyes of this invention are effective electron acceptors and spectral sensitizers for photographic direct positive silver halide emulsions. Closely related pyrylium cyanine dyes, such as those pyrylium cyanine dyes containing a desensitizing carbazole nucleus or an imidazo[4,5-b]quinoline nucleus, produce too high minimum densities (in exposed areas) to be practical electron acceptors for direct positive emulsions. The dyes of this invention unexpectedly result in low minimum densities while providing effective spectral sensitization.

By substituting other dye compounds of the invention as defined in Formulas I and II above into the procedure of the above examples, similar fogged, direct positive photographic silver halide emulsion and photographic elements may be prepared.

The following Examples A through G illustrate the preparation of some of the intermediates employed in the preparation of the dye compounds of the invention.

EXAMPLE A 4,6-di-(4-ethoxyphenyl)-2-methylpyrylium fluoroborate O CH:

C2H50 B1349 To a mixture of 4-ethoxyacetophenone (82.1 g.) and acetic anhydride (150 ml.) boron trifiuoride ethyl etherate (150 ml.) is added and the mixture heated at 50 C. for 24 hours, after which it is allowed to cool, diluted with ether and chilled. The product is collected on the filter. The yield is 42 g. (39%). The brownish orange crystals melt at 226-228 C. with decomposition.

EXAMPLE B 6,7-dihydro-2,4-diphenyl-SH-cyclopenta[b]pyrylium perchlorate H2 (not 69 CuHs H2 To a solution of chalcone (69 g.) in ether (275 ml.) perchloric acid (70%, 50 ml.) is added slowly and the mixture chilled. To the chilled mixture, acetic anhydride (220 ml.) is added dropwise during two hours; the mixture is allowed to reach room temperature and cyclopentanone (30 g.) is added and the mixture stirred for two hours. The product is collected on the filter and washed with acetic acid and then with ether. The yield is 39 g. (31% the brownish orange crystals melt at 240- 241 C. with decomposition.

EXAMPLE C 4-methyl-2,6-diphenylpyrylium perchlorate Calls EXAMPLE D 1,2,3,4-tetrahydroxyanthylium perchlorate To a cooled mixture of perchloric acid (70%, 30 ml.) and acetic acid (300 ml.), a mixture of salicylaldehyde (24.4 g.) and cyclohexanone (20 g.) is slowly added. The product is collected on the filter and washed with ether. The yield is 18 g. (31% The brown crystals melt at 168169 C. with decomposition.

8,9,10,11 tetrahydro-benzo[a]xanthylium perchlorate is similarly prepared from 2-hydroxy-1-naphthaldehyde. The yield is 21%; the pale greenish crystals melt at 221- 222 C. with decomposition.

EXAMPLE E 4-methyl-2-phenyl-l-benzopyrylium perchlorate 0104 Cam To a stirred suspension of ferric chloride (108 g.) in acetic acid ml.) a mixture of acetophenone (60 g.) and 2'-hydroxyacetophenone (68 g.) is added: hydrochloric acid (100 ml.) is then added and the mixture heated under reflux for 3 hours. The product is collected on the filter and washed with ether. The yield is 54 g. (28%); the pale green crystals melt at l69l70 C. with decomposition.

EXAMPLE F 7 -ethoxymethylene-6,7-dihydro-2,4-diphenyl-H-cyclopenta [b] pyrylium perchlorate II 0110mm A mixture of 6,7 dihydro 2,4 diphenyl 5H cyclopenta[b]pyryl.ium perchlorate (19 g.), ethylorthoacetate ml.) and acetic anhydride (100 ml.) is heated under reflux for 1 0 minutes. The mixture is allowed to cool and the product collected on the filter and washed with acetic acid and then with ether. The yield is 11.8 g. (55%). The dark brown crystals melt at 173-174 C. with decomposition.

EXAMPLE G 6-ethoxy-2-phenyl-1=benzothiapyrylium fluoroborate 9 S, CaHs To l-thioflavone (8 g.) in methylene chloride (150 ml.) is added triethyl oxonium fluoroborate (6 g.) and the mixture is stirred and left overnight in an ice box. Then 50 ml. of methylene chloride is added to the mixture and the product is filtered out and washed with ether. The yield of the above compound is 6.5 g. (55%) of yellow crystals, M.P. 126-128 C.

The intermediate l-thioflavone for above Example G is prepared by heating a mixture of benzene thiol (10.5 g.), ethylbenzoyl acetate (25.0 g.) and polyphosphoric acid, (350 g.) with occasional stirring, on a steam bath for a period of about one hour. The mixture is heated for another 3 hours at 90-100 C. and then poured over 500 g. of ice, stirred, the product filtered out and washed. The yield of l-thiaflavone is 22 g. (92% M.P. 5557 C.

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 oxy 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 colorforming 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 Jelley et a1. U.S. Pat. 2,322,027, issued June 15, 1943, Fierke et a1. U.S. Pat. 2,801,171, issued July 30, 1957, Fisher U.S. Pats. 1,055,155 and 1,102,028, issued Mar. 4, 1913 and June 30, 1914, respectively, and Wilmanns U.S. Pat. 2,186,849, issued J an. 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 variations and modifications can be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

We claim:

1. A fogged direct positive photographic silver halide emulsion containing a methine \dye selected from those 'nitroindolenine, nitropyridine and nitroquinoline; and (b) a pyrazole nucleus, joined at the 4-carbon atom thereof to the methine linkage.

2. A direct positive emulsion as defined by claim 1 wherein the first nucleus of said dye is a pyrylium nucleus; said second nucleus is a pyrazole nucleus; and, said linkage is a dimethine linkage.

3. A direct positive emulsion as defined by claim 1 wherein the first nucleus of said dye is a pyrylium nucleus; said second nucleus is said nitro-containing nucleus; and, said linkage is a monomethine linkage.

4. A direct positive emulsion as defined by claim 1 wherein the first nucleus of said dye is an 8,9,10,11- tetrahydrobenzo [a]thiaxanthylium nucleus, and said second nucleus is said pyrazole nucleus.

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

6. A direct positive emulsion in accordance with claim 1 in which the said silver halide is present in the form of reduction and gold fogged silver halide grains.

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

8. 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 DK-SO developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

potassium cyanide-50 mg. acetic acid (glacial)-3.47 cc. sodium acetate-41.49 g. potassium bromide1 19 mg. water to 1 liter 9. A direct positive, photographic emulsion in accordance with claim 1 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 size.

10. A fogged direct positive photographic silver halide 15 emulsion containing a methine dye selected from those represented by one of the following general formulas:

wherein one and only one of A and A represents a member selected from the group consisting of (a) a group of the formula:

and (b) a group of the formula CNR7 --CH=CH-C and the other of said A and A represents a member selected from the group consisting of a hydrogen atom, an alkyl group and an aryl group; n and In each represents a positive integer of from 1 to 2; R represents a member selected from the group consisting of an alkyl group, and an aryl group; R through R, each represents a member selected from the group consisting of a hydrogen atom, an alkyl group and an aryl group; and, R and R when taken together, represent the atoms to complete a fused ring selected from a fused phenyl ring and a fused naphthyl ring; D represents a member selected from the group consisting of an oxygen atom and a sulfur atom, X represents an acid anion, Q represents a member selected from the group consisting of an ethylene and a trimethylene group; and Z represents the non-metallic atoms necessary to complete a nucleus selected from the group consisting of nitrobenzothiazole, nitrobenzoxazole, nitrobenzoselenazole, nitroindolenine, nitropyridine and nitroquinoline.

11. A direct positive emulsion as defined by claim wherein said D of said dye represents an atom of oxygen.

12. A direct positive emulsion as defined by claim 10 wherein said Q of said dye represents a trimethylene group.

13. A direct positive emulsion as defined by claim 10 wherein said A of said dye represents said (b) group.

14. A direct positive emulsion as defined by claim 10 wherein said A of said dye represents said (a) group.

15. A direct positive emulsion as defined by claim 10 wherein said R and R of said dye taken together 16 represent the atoms to complete a fused ring selected from a fused phenyl ring and a fused naphthyl ring.

16. A direct positive emulsion as defined by claim 10 wherein said Z of said dye represents a nucleus selected from the group consisting of a nitrobenzothiazole nucleus, a nitrobenzoxazole nucleus and a nitrobenzoselenazole nucleus.

17. A direct positive emulsion as defined by claim 10 wherein said dye is selected from the group consisting of 2- [2- 3,5 -dimethyl-1-phenyl-4-pyrazolyl) vinyl] -4,6-

di- 4-ethoxyphenyl pyrylium salt;

8-[ (3,5 -dimethyll -phenyl-4-pyrazolyl methylene] 8 ,9, l 0,1 l-tetrahydrobenzo [a] xanthylium salt; and

3 '-methyl-6-nitro-2-phenyl-4-( l-benzopyrylo -2- thiacyanine salt.

18. A direct positive emulsion in accordance with claim 10 in which the said silver halide is present in the form of chemically fogged silver halide grains.

19. A direct positive emulsion in accordance 'With claim 10 in which the said silver halide is present in the form of reduction and gold fogged silver halide grains.

20. A direct positive emulsion in accordance with claim 10 containing a photographic color coupler.

21. A direct positive photographic emulsion in accordance with claim 10 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 in Kodak DK-5O developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

potassium cyanide-50 mg. acetic acid (glacial)3.47 cc. sodium acetate1l.49 g. potassium bromide119 mg. water to 1 liter 22. A direct positive photographic emulsion in accordance with claim 10 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 size.

23. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 1.

24. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 8.

25. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 9.

'26. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 10.

27. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 21.

28. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 22.

29. A photographic silver halide emulsion containing a methine dye comprising first and second heterocyclic nuclei joined by a methine linkage selected from the group consisting of monomethine, dimethine and trimethine; the first of said nuclei being selected from the group consisting of a pyrylium and a thiapyrylium nucleus, and said second nucleus being selected from the group consisting of (a) a nucleus selected from the group consisting of nitrobenzothiazole, nitrobenzoxazole, nitrobenzoselenazole, nitroindolenine, nitropyridine and nitroquinoline; and, (b) a pyrazole nucleus, joined at the 4-carbon atom thereof to the methine linkage.

1 7 30. A photographic silver halide emulsion containing a methine dye selected from those represented by one of the following general formulas:

Rs I mlolA X and the other of said A and A represents a member selected from the group consisting of a hydrogen atom,

an alkyl group and an aryl group; n and m each represents a positive integer of from 1 to 2; R represents a member selected from the group consisting of an alkyl group, and an aryl group; R through R; each represents a member selected from the group consisting of a hydrogen atom, an alkyl group and an aryl group, and, R and R when taken together, represent the atoms to complete a fused ring selected from a fused phenyl ring and a fused naphthyl ring; -D represents a member selected from the group consisting of an oxygen atom and a sulfur atom, X represents an acid anion; Q represents a member selected from the group consisting of an ethylene and a trimethylene group; and Z represents the non-metallic atoms necessary to complete a nucleus selected from the group consisting of nitrobenzothiazole, nitrobenzoxazole, nitrobenzoselenazole, nitroindolenine, nitropyridine and nitroquinoline.

31. A photographic silver halide emulsion containing a methine dye selected from the group consisting of 2- [2- (3 ,5 -dimethyll-phenyl-A-pyrazolyl) vinyl] -4,6-

di- (4-ethoxyphenyl)pyrylium salt; 8-[ (3,5-dimethyl-1-phenyl-4-pyrazolyl) methylene] 8,9,10,ll-tetrahydrobenzo [a]xanthylium salt; and 3 '-methyl-6'-nitro-2-phenyl-4-( l-benzopyrylo) -2- thiacyanine salt.

32. A photographic element comprising a support having thereon at least one layer containing a. photographic emulsion of claim 31.

References Cited UNITED STATES PATENTS 3,148,067 '9/1964 Reynolds 96109 3,250,615 5/ 1966 Van Allen et a1 96-88 NORMAN G. TORCHIN, Primary Examiner 'R. E. FIGHTER, Assistant Examiner U.S. Cl. X.R.