US3542548A - Novel cyanine dyes for the sensitization of organic photoconductors - Google Patents

Description

United States Patent Ofice 3,542,548 Patented Nov. 24, 1970 US. Cl. 96--1.6 33 Claims ABSTRACT OF THE DISCLOSURE Organic photoconductors are spectrally sensitized with a cyanine dye having a pyrrolo[2,3-b]quinoxaline nucleus or a pyrrolo[2,3-b]pyrazine nucleus, joined at the 3-carbon atom thereof, to the methine linkage of the cyanine dye.

This invention relates to electrophotography, and more particularly to materials and elements useful in the electrophotographic process.

Elements useful in the electrophotographic process commonly comprise an electrically conductive support bearing a stratum including a photoconductive insulating layer which has a resistivity substantially greater in the dark than in light actinic thereto. Such elements can be used in electrophotographic processes, for example, by first adapting the element in the dark to obtain a uniformly high resistivity in the photoconductive insulating layer, and electrostatically charging the element in the dark to obtain a relatively high potential which may be either negative or positive in polarity. The element can then be exposed to a light pattern which lowers the resistivity and thereby the charge density of the illuminated areas imagewise in proportion to the intensity of illumination incident upon each point of the illuminated areas. A latent electrostatic image is obtained. Visible images can be formed from the latent electrostatic image in any convenient manner, such as by dusting with a finely divided, fusible pigment the particles of which bear an electrostatic charge opposite that remaining on the surface of the photoconductive insulating layer. Thereafter, the pigment particles can be fused to the surface to provide a permanent image.

Various photoconductive substances have been employed in photographic elements and processes of the type described above. Typical inorganic photoconductive materials include selenium and zinc oxide. Such inorganic photoconductive materials have irfiierent disadvantages, such as an inability to be readily adapted totreflex copying systems, or to produce images on transparent supports except by indirect means. Organic photoconductors avoid such disadvantages, but generally have relatively poor sensitivity to visible radiation. It has been proposed to increase the spectral sensitivity of organic photoconductors with certain cyanine or merocyanine dyes, for example, such as those listed in Table D hereinafter. The spectral sensitivity imparted by such dyes is weak. It, therefore appears highly desirable to provide effective spectral sensitizers for organic photoconductors.

One object of this invention is to provide novel sensi tized organic photoconductors.

Another object of this invention is to provide novel spectrally sensitized organic photoconductor materials.

Still another object of this invention is to provide novel compositions of matter comprising organic photoconductors and certain spectral sensitizers.

A further object of this invention is to provide novel compositions of matter comprising organic photoconductor, binder and certain spectral sensitizers for the organic photoconductor.

Still another object of this invention is to provide a novel electrophotographic material including a conductive support having coated thereon an insulating layer containing spectrally sensitized organic photoconductor.

A further object of this invention is to provide methods for spectrally sensitizing organic photoconductors.

Still other objects of this invention will be apparent from the following disclosure and the appended claims.

In accordance with one embodiment of this invention, novel compositons of matter are provided comprising organic photoconductors spectrally sensitized with the dyes defined more fully below. These compositions can be incorporated in a suitable binder and coated on a conductive support for use in electrophotography.

In another embodiment of this invention, compositions of matter are provided comprising organic photoconductors spectrally sensitized with the dyes described below, dispersed in an insulating binder. These compositions of matter can be coated on a conductive support and used in electrophotographic processes.

In still another embodiment of this invention, electrophotographic materials are provided comprising a conductive support having coated thereon a layer comprising an insulating binder, an organic photoconductor and a spectral sensitizing quantity of a dye defined more fully below.

In another embodiment of this invention, a method is provided for spectrally sensitizing organic photoconductors which comprises mixing a dye of the type described below with an organic photoconductor, in a concentration sufiicient to effectively spectrally sensitize the organic photoconductor. Preferably, the dye and organic photoconductor are mixed in a suitable solvent.

The spectral sensitizing dyes which are employed in this invention are certain cyanine dyes containing certain pyrazole nuclei which, when incorporated in a test negative gelatin silver bromoiodide emulsion consisting of 99.35 mole percent bromide and .65 mole percent iodide, at a concentration of 0.2 millimole of dye per mole of silver halide, desensitize the emulsion more than 0.4 log B when the test emulsion is coated on a support, exposed through a step wedge in a sensitometer (to obtain D to light having a wavelength of 3165 mm., processed for three minutes at 20 C. in Kodak Developer D-19, and is fixed, washed and dried. As used herein and in the appended claims, the test negative silver bromoiodide emulsions are prepared as follows:

In a container with temperature control is put a solution with the following composition:

G. Potassium bromide Potassium iodide 5 Gelatin 65 Water, 1700 cc.

And in another container is put a filtered solution consisting of:

G. Silver nitrate 200 Water, 2000 cc.

3 stirrer. The precipitation is conducted over a period of minutes.

The developer employed in the test referred to above is Kodak Developer D-l9 which has the following composition:

G. N-methyl-p-arninophenol sulfate 2.0 Sodium sulfite, desiccated 90.0 Hydroquinone 8.0 Sodium carbonate, monohydrated 52.5 Potassium bromide 5.0

Water to make 1.0 liter As indicated above, the cyanine dyes employed in this invention desensitize conventional negative silver halide emulsions. Such emulsions are inherently sensitive to blue radiation. The present dyes reduce that sensitivity. In addition, these dyes fail to provide practical spectral sensitization for such emulsions. Therefore, it was quite unexpected to find that they spectrally sensitized organic photoconductors.

Another characteristic of the cyanine dyes of this invention is that they are substantially non-photoconductive. The term substantially non-photoconductive as used herein means that no image is formed when a solution of 0.002 g. of the dye and 0.5 g. of polyester binder (described in Examples 1 to 2 below) are dissolved in 5.0 ml. of methylene chloride, and is coated and tested (in the absence of any photoconductor) as described in Examples 1 to 2 below.

The cyanine dyes of this invention increase the speed of organic photoconductors by extending or increasing the response of the photoconductor to visible radiation (i.e., radiation in the range of about 400 nm. to 2700 nm.) In the concentrations used, the dyes herein appear to function as spectral sensitizers when employed with efiicient organic photoconductors. When the organic photoconductor used is poor or inefficient, the dyes seem to function as speed increasing compounds as well as spectral sensitizers.

The cyanine dyes that are useful in practicing the invention include those comprising first and second 5- to 6-membered nitrogen containing heterocyclic nuclei joined together by a methine linkage containing from 2 to 3 carbon atoms in the methine chain (including those link- 4 ages wherein a methine group is substituted by alkyl, aryl or heterocyclic substituents); the first of said nuclei being selected from a pyrrolo[2,3-b]quinoxaline nucleus or a pyrrolo[2,3-b1pyrazine nucleus joined in each case at the 3-carbon atom thereof to said linkage; and, said second nucleus being selected from (a) a heterocyclic nitrogen containing nucleus of the type used in the production of cyanine dyes, when said linkage is a dimethine linkage, and (b) when said linkage is a trimethine linkage, said second nucleus is selected from the group consisting of a Z-arylindole nucleus, a pyrrolo[2,3-b]quinoxaline nucleus and a pyrrolo[2,3-b1pyrazine nucleus, each of said nuclei being joined at the 3-carbon atom thereof to said trimethine linkage, to complete said cyanine dye. Preferably, the second nucleus is an electron-accepting nucleus.

The preferred cyanine dyes that are useful herein include those represented by the following general formula:

wherein n represents a positive integer of from 1 to 2; L represents a methine linkage, e.g., --Cl-I=, -C (CH -C(C H -C(3indolyl)=; C(2-pyridyl)=;

4 'C(2-thienyl)=; etc.; 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., fl-hydroxyethyl, w-hydroxybutyl, etc., an alkoxyalkyl group, e.g., p-methoxyethyl, w-butoxybutyl, etc., a carboxyalkyl group e.g., fi-carboxyethyl, w-carboxybutyl, etc., a sulfoalkyl group, e.g., [3- sulfoethyl, w-sulfobutyl, etc., a sulfatoalkyl group, e.g., B- sulfatoethyl, w-sulfatobutyl, etc., an acyloxyalkyl group, e.g., fl-acetoxyethyl, 'y-acetoxypropyl, w-butyryloxybutyl, etc., an alkoxycarbonylalkyl group, e.g., ,B-methoxycarbonylethyl, w-ethoxycarbonylbutyl, etc., or an aralkyl group, e.g., benzyl, phenethyl, etc.; an alkenyl group, e.g., allyl, l-prophenyl, Z-butenyl, etc.; or, an aryl group, e.g., phenyl, tolyl, naphthyl, methoxyphenyl, chlorophenyl, etc. R represents an alkyl group, e.g., methyl, ethyl, propyl, isopropyl, butyl, decyl, dodecyl, etc., or an aryl group, e.g., phenyl, tolyl, naphthyl, etc.; R and R each 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, cyclohexyl, decyl, dodecyl, etc., or an aryl group e.g., phenyl, tolyl, naphthyl, chlorophenyl, nitrophenyl, methoxyphenyl etc.; and, R and R taken together with the two fused nuclei to which they are attached, can represent the non-metallic atoms necessary to complete a pyrrolo[2,3-b]quinoxaline nucleus; R represents a hydrogen atom or an aryl group, e.g., phenyl, tolyl, naphthyl, chlorophenyl, nitrophenyl, methoxyphenyl, etc.; X represents an acid anion, e.g., chloride, bromide, iodide, thiocyanate, sulfamate, perchlorate, ptoluenesulfonate, methyl sulfate, ethyl sulfate, etc.; and Z represents the non-metallic atoms necessary to complete, a heterocyclic nucleus of the type used in cyanine dyes, and preferably an electron-accepting nucleus, containing from 5 to 6 atoms in the heterocyclic ring, 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, 5-phenylthiazole, 4,5-dimethylthiazole, 4,5-diphenylthiazole, 4-(2-thienyl)thiazole, benzothiazole, 4-chlorobenzothiazole, 4- or S-nitrobenzothiazole, 5-chlorobenzothiazole, 6-chlorobenzothiazole, 7-chlorobenzothiazole, 4-methylbenzothiazole, 5- methylbenzothiazole, 6-methylbenzothiazole, 6-nitrobenzothiazole, S-bromobenzothiazole, 6-bromobenzothiazole, S-chloro-6-nitrobenzothiazole, 4-phenylbenzothiazole, 4- rnethoxybenzothiazole, S-methoxybenzothiazole, 6-methoxybenzothiazole, 5-iodobenzothiazole, 6-iodobenzothiazole, 4-ethoxybenzothiazole, S-ethoxybenzothiazole, tetrahydrobenzothiazole, 5,6-dimethoxybenzothiazole, 5,6-dioxymethylenebenzothiazole, S-hydroxybenzothiazole, 6- hydroxybenzothiazole, naphtho[2,1-d]thiazole, naphtho [1,2-d]thiazole, naphtho[2,3-d]thiazole, S-methoxynaphtho[2,3-d]thiazole, 5-ethoxynaphtho[l,2-d]thiazole, 8- methoxynaphtho [2,1-d]thiazole, 7-methoxynaphtho [2, ldJthiazole, 4'-methoxythianaphtheno-7,6'4,5-thiazole, nitro group substituted naphthothiazoles, etc.; an oxazole nucleus, e.g., 4-methyloxazole, 4-nitro-oxazole, S-methyloxazole, 4-phenyloxazole, 4,5-diphenyloxazole, 4-ethyloxazole, 4,5-dimethoxazole, S-phenyloxazole, benzoxazole, S-chlorobenzoxazole, S-methylbenoxazole, 5-phenylbenzoxazole, 5- or 6-nitrobenzoxazo1e, 5-chloro-6-nitrobenz oxazole, 6-methylbenzoxazole, 5,6-dimethylbenzoxazole, 4,6-dimethylbenzoxazole, S-methoxybenzoxazole, S-ethoxybenzoxazole, 5 -chlorobenzoxazole, 6-methoxybenzoxazole, S-hydroxybenzoazole, 6-hydroxybenzoxazole, naphth [2,1-d]oxazole, naphth[1,2-d]oxazole, nitro substituted naphthoxazoles, etc.; a selenazole nucleus, e.g., 4-methylselenazole, 4-nitroselenazole, 4-phenylselenazole, benzo selenazole, S-chlorobenzoselenazole, S-methoxybenzoselenazole, S-hydroxybenzoselenazole, 5- or 6-nitrobenzoselenazole, 5-chloro-6-nitrobenzoselenazole, tetrahydrobenzoselenazole, naphtho[2,1-d]selenazole, naphtho[1,2- d]selenazole, nitro substituted naphthoselenazoles, etc.; a thiazoline nucleus, e.g., thiazoline, 4-methylthiazoline, 4- nitrothiazoline, etc.; a pyridine nucleus, e.g., 2-pyridine, S-methyl-Z-pyridine, 4-pyridine, 3-methyl-4-pyridine, nitro group substituted pyridines, etc.; a quinoline nucleus, e.g., 2-quinoline, 3-methyl-2-quinoline, 5-ethyl-2-quinoline, 6- chloro 2 quinoline, 6 nitro 2 quinoline, 8 chloro- 2 quinoline, 6 methoxy 2 quinoline, 8 ethoxy- 2 quinoline, 8 hydroxy 2 quinoline, 4 quinoline, 6- methoxy-4-quinoline, 6-nitro-4-quinoline, 7-methyl-4- quinoline, 8-chloro-4-quinoline, l-isoquinoline, 6-nitro-1- 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-alkylimidazole, lalkyl-4-phenylimidazole, l-alkyl 4,5-dimethylimidazole, benzimidazole, l-alkylbenzimidazole, 1-aryl-5,6-dichlorobenzimidazole, l-alkyl-lH-naphthimidazole, 1-aryl-3H- naphth[1,2-d]imidazole, 1 alkyl S-methoxy-lH-naphth- [1,2 d]imidazole or an imidazo[4,5 b]quinoxaline nucleus, e.g., 1,3-dialkylimidazo[4,5-b]quinoxaline such as 1,3 diethylimidazo [4,5-b] quinoxaline, 6 chloro 1,3-diethylimidazo[4,5-b] quinoxaline, etc., 1,3-dialkenylirnidazo [4,5-b1quinoxaliue such as 1,3-diallylimidazo [4,5-b]quinoxaline, 6 chloro-1,3 diallylimidazo[4,5-b]quinoxaline, etc., 1,3-diarylimidazo[4,5-b]quinoxaline such as 1,3-diphenylimidazo [4,5 -b] quinoxaline, 6-ch1orol ,S-diphenylimidazo[4,5-b]quinoxaline etc.; a 1,3,3-trialkyl-3H-pyrrolo[2,3-b]pyridine nucleus, e.g., 1,3,3-trimethyl-3H-pyrrolo [2,3 -b] pyridine, 1,3 ,3 -triethyl-3H-pyrrolo [2,3 -b] pyridine, etc.; a thiazole [4,5-b1quinoline nucleus; and the like. Nuclei wherein Z in above Formula I represents an imidazo[4,5-b]quinoxaline nucleus, a 1,3,3-trialkyl-3H pyrrolo[2,3-b]pyridine nucleus, a thiazolo [4,5-b]quinoline nucleus, a nitro substituted thiazole, oxazole, selenazole, thiazoline, pyridine, quinoline, 1,3,3-trialkylindolenine, or imidazole nucleus are electron-accepting nuclei. Dyes such as defined above containing such nuclei are the preferred spectral sensitizing dyes for photoconductor compositions and elements of this invention.

As used herein and in the appended claims, electron accepting 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 grams 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 D-19 at 20 C., the composition of which is given above. Preferably, the electron-accepting nuclei are those which, when converted to a symmetrical carbocyanine dye and tested as just described above, essentially completely desensitize the test emulsion to blue radiation. Substantially complete desensitization as used herein, results in at least at 90 percent, and preferably a 95 percent loss of speed to blue radiation.

Another highly useful class of cyanine dyes that function as spectral sensitizers in this invention include those represented by the following general formula:

wherein R R R R R and X are as previously defined, R represents an alkyl group (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl,

ethyl, propyl, isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl etc., or an aryl group, e.g., phenyl, tolyl, naphthyl, chlorophenyl, nitrophenyl, methoxyphenyl, etc., or a heterocyclic radical containing from 5 to 6 atoms in the heterocyclic ring and having a hetero nitrogen, oxygen or sulfur atom, preferably a heterocyclic radical selected from pyridyl (e.g., 2-, 3- or 4-pyridyl), 3-indolyl, of 2-thienyl; R represents a hydrogen atom or an aryl group, e.g., phenyl, tolyl, naphthyl, chlorophenyl, nitrophenyl, methoxyphenyl, etc.; and D repersents the non-metallic atoms necessary to complete a 2-arylindole nucleus (e.g., a 1-a1kyl (or aryl)-2-phenylindole, a l-alkyl (or aryl)-5 nitro-Z-phenylindole, etc.) a pyrrolo[2,3-b]quinoxaline nucleus (e.g., 1-butyl-7-chloropyrrolo[2,3-b]quinoxaline, 1-methyl2-p-tolylpyrrolo[2,3-b1quinoxaline, etc.) or a pyrrolo[2,3b]pyrazine nucleus (e.g., 1-methylpyrrolo[2, 3-b]pyrazine, etc.).

The cyanine dyes defined by Formula I above are conveniently prepared, for example, by heating a mixture of wherein R R R and R are as previously defined, in approximately equimolar proportions, in a solvent medium such as acetic anhydride. The crude dyes are separated from the reaction mixtures and purified by one or more recrystallizations from appropriate solvents such as methanol alone or acidified with an acid such as p-toluenesulfonic acid, perchloric acid, etc.

The intermediates defined by Formul IV above may be prepared by means of the Vilsmeier reaction. For example by reacting (1) a compound of the formula:

or a compound of the formula:

wherein R R R R and X are as previously defined, with (2) a complex of phosphoryl chloride, phosgene, oxalyl chloride, etc., and dimethyl formamide, in excess dimethylformamide as solvent, in approximate proportions of 1 mole of (1) to 3 or more moles of (2). The reaction mixtures are cooled, diluted with an ice-water mixture, and then made alkaline by addition of aqueous allgali metal hydroxide solution such as aqueous sodium hydroxide. The product is then separated by conventional methods, for example, by extraction of the mixture with a water-insoluble solvent such as chloroform, the residue being purified, if desired, by one or more re- '7 crystallizations from appropriate solvents such as dimethyl formamide.

The cyanine dyes defined for Formula II above are conveniently prepared, for example, by heating a mixture of (l) a compound of Formula IV above and (2) a compound of the formula:

(VII) wherein D, R R and R are as previously defined, in approximately equimolar proportions, in a solvent medium such as acetic anhydrides containing a strong mineral acid such as perchloric acid. After cooling and diluting with ether, the solid which separates is recrystallized.

Further details for the preparation of the dyes herein can be had by reference to our copending application Ser. No. 705,595, filed Feb. 15, 1968, wherein such dyes and their preparations are described.

Included among the dyes defined above are the following typical dye compounds. The method for preparing Dye No. I is included in Table A below to illustrate, in general, how the dyes herein are prepared.

pyrrolo[2,3 b]quinoxalinoearboeyanine bromide.

(VIII). 1-buty1-7-ehloro-1,3-trimethyl5-nitroindo-3-pyrrolo [2,3-b]quinoxalinocarboeyanine bromide.

(IX) 3-ethyl-1-methyl-6 -nitro-2-p-tolyl-3-pyrr0l0-[2,3 b]- quinoxalinothiacarbocyanine p-toluenesuli'onate.

(X) 1,3-diallyl-1-methyl-Zp-tolylimidaz0[4,5 b]quin0xalino-3- pyrrolo[2,3-b]quinoxalinocarbocyanine p-toluenesulfonate.

(XI) 6-ehloro-1-methyl-1,3-di henyl-2-p-tolylimidazo-[4,5-b]

quinoxalino-3-pyrrolo 2,3-b]quinoxalino-earbocyannine p-toluenesulfonate.

(XII) 1,1,3,3-tetramethyl-5-nitro-2-p-t0lylindo-3-pyrr0l0[2,3b]-

quinox alinocarbocyanine p-toluenesulfonate.

(XIII)- 1,1',3,3-tetramethyl-2-p-tolylpyrrolo[2,3-b] pyrido-3-pyrrolo 2,3-b1quinoxacarbocyannine perchlorate.

(XIV) 1,1-dimethyl-2,8-diphenyl-W-ptolyl-Zt-indolo 3-pyrrolo [2,3-b]quinoxaliuoearbocyanine perchlorate.

Dye N0.

mide. (XXVIII) S-ethyl-l,1-dimethyl-5,6-diphenyl-3-pyrrol0[2,3-b]pyrazino- 3'-pyrrolo[2,dbl-quinoxalinocarbocyanine bromide. (XXIX) Zethyl-I,1-dimethyl-S-(Z-naphthyl)-3,3-pyrrolo[2,3-b]

pyrazinoearbocyanine bromide.

Compound 1 l-ethyl 3 forlnylpyrrolo[2,3-b1quinoxaline (0.56 g., 1 mol.) and 3-ethy1'2-methy1-6-nitrobenz0thiazolium p-toluenesulfonate (0.99 g., 1 mol.) in acetic anhydride (10 ml.) are heated at reflux for 1 minute. The cooled solution is slowly diluted with excess ether and the solid which is precipitated is collected and washed with ether. After one recrystallization from methanol, the yield of purified dye is 0.77 g. (51%), M.P. 2Sl282 C., dec.

Dyes such as illustrated above can be used alone, or a combination of one or more of the above described dyes can be used to impart the desired spectral sensitivity. All of them are spectral sensitizers for organic photoconductors. Suitable organic photoconductors which are effectively spectrally sensitized by such dyes include both monomeric and polymeric organic photoconductors. The invention is particularly useful in increasing the speed of organic photoconductors which are substantially insensitive, or which have low sensitivity (e.g., a speed less than but generally less than 10 when treated as described in Examples 1 to 6 below) to radiation in 400 to 700 nm.

An especially useful class of organic photoconductors is referred to herein as organic amine photoconductors. Such organic photoconductors have as a common structural feature at least one amino group. Useful organic photoconductors which can be spectrally sensitized in accordance with this invention include, therefore, arylamine compounds comprising (1) diarylamines such as diphenylamine, dinaphthylamine, N,N'-diphenylbenzidine, N-phenyl-l-naphthylamine; N-phenyl-Z-naphthylamine; N,N-diphenyl-pphenylenediamine; 2-carboxy 5 chloro-4'-methoxydiphenylamine; p-anilinophenol; N,N'-di-2-naphthylp-phenylene diamine; 4,4 benzylidene bis(N,N-diethylm-toluidine), those described in Fox U.S. Pat. No. 3,240,- 597 issued Mar 15, 1966, and the like, and (2) triarylamines including (a) non-polymeric triarylamines, such as triphenylamine, N,N,N,N'-tetraphenyl rn phenylenediamine; 4-acetyltriphenylamine, 4-hexanoyltriphenylamine; 4 lauroyltriphenylamine; 4-hexyltriphenylamine, 4 dodecyltriphenylamine, 4,4 bis(diphenylamino)-benzil, 4,

4'-bis(diphenylamino)-benzophenone, and the like, and (b) polymeric triarylamines such as poly[N,4- (N,N',N' triphenylbenzidine)]; polyadipyltriphenylamine, polysebacyltriphenylamine; polydecamethylenetriphenylamine; poly N (4-vinylphenyl)-diphenylamine, poly N (vinylphenyl)-u,a'-dinaphthylamine and the like. Other useful amine-type photoconductors are disclosed in U.S. Pat. No. 3,180,730, issued Apr. 27, 1965.

Other very useful photoconductive substances capable of being spectrally sensitized in accordance with this in vention are disclosed in Fox U.S. Pat. No. 3,265,496, is-

sued Aug. 9, 1966, and include those represented by the following general formula:

wherein A represents a mononuclear or polynuclear divalent aromatic radical, either fused or linear (e.g., phenylene, naphthylene, biphenylene, binaphthylene, etc.), or a substituted divalent aromatic radical of these types wherein said substituent can comprise a member such as an acyl group having from 1 to about 6 carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from 1 to about 6 carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from 1 to about 6 carbon atoms (e.g., methoxy, ethoxy, propoxy, pentoxy, etc.), or a nitro group; A represents a mononuclear or polynuclear monovalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.); or a substituted monovalent aromatic radical wherein said substituent can comprise a member, such as an acyl group having from 1 to about 6 carbon atoms (e.g., acetyl, pro pionyl, butyryl, etc.), an alkyl group having from 1 to about 6 carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from 1 to about 6 carbon atoms (e.g., methoxy, propoxy, pentoxy, etc.), or a nitro group; Q can represent a hydrogen atom, a halogen atom or an aromatic amino group, such as A'NH-; b represents an integer from 1 to about 12, and G represents a hydrogen atom, a mononuclear or polynuclear aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biph enyl, etc.), a substituted aromatic radical wherein said substituent comprises an alkyl group, an alkoxy group, an acyl group, or a nitro group, or a poly(4-vinylphenyl) group which is bonded to the nitrogen atom by a carbon atom of the phenyl group. Certain nitrogen heterocyclic compounds are also useful photoconductors in the invention such as, for example, 1,3,5-triphenyl-2-pyrazo1ine, 2,3, 1,5- tetraphenylpyrrole, etc.

Polyarylalkane photoconductors are particularly useful in producing the present invention. Such photoconductors are described in US. Pat. No. 3,274,000; French Pat. No. 1,383,461 and in a copending application of Seus et al., Ser. No. 624,233, Photoconductive Elements Containing Organic Photoconductors filed Mar. 20, 1967. These photoconductors include lcucobases of diaryl or triaryl methane dye salts, 1,1,l-triarylalkanes wherein the alkane moiety has at least two carbon atoms and tetraarylmethanes, there being substituted an amine group on at least one of the aryl groups attached to the alkane and methane moieties of the latter two classes of photoconductors which are non-leuco base materials.

Preferred polyaryl alkane photoconductors can be represented by the formula:

wherein each of D, E and G is an aryl group and J is a hydrogen atom, an alkyl group, or an aryl group, at least one of D, E and G containing an amino substituent. The aryl groups attached to the central carbon atom are preferably phenyl groups, although naphthyl groups can also be used. The aryl groups can contain substituents such as alkyl and alkoxy, typically having 1 to 8 carbon atoms, hydroxy, halogen etc. in the ortho, meta or para positions, ortho-substituted phenyl being preferred. The aryl groups can also be joined together or cyclized to form a fluorene moiety, for example. The amino substituent can be represented by the formula wherein each R can be an alkyl group typically having 1 to 8 carbon atoms, a hydrogen atom, an aryl group, or together the necessary atoms to form a heterocyclic amino group typically having 5 to 6 atoms in the ring such as morpholino, pyridyl, pyrryl, etc. At least one of D, E and G is preferably p-dialkylaminophenyl group. When I is an alkyl group, such an alkyl group more generally has 1 to 7 carbon atoms.

Representative useful polyarylallkane photoconductors include the compounds listed below:

.. 4,4-bis(dimethylamino)-1,1,1-triphenylethanc.

(14) 1-(4-N,N-dimethylaminophenyl)-1,l-diphenylethane. (15) 4-dimethylaminotetraphenylmethane. (13) 4-diethylaminotetraphenyhnethane.

As described herein a wide variety of photoconductor compounds can be spectrally sensitized with the dyes referred to above. Some organic photoconductors will, of course, be preferred to others; but in general useful results may be obtained from substantially all of the presently known organic photoconductors.

The following Table C comprises a partial listing of US. patents describing such organic photoconductors and compositions which can be used in place of those more particularly described herein.

TABLE 0 Patent Inventor Issued Numbers Noe et a1 Feb. 25, 1964 3,122, 435 Sus et a1. Mar. 31, 1964 3,127, 266 Schlesinger Apr. 21, 1964 3,130, 046 Cassiers Apr. 28, 1964 3, 131,060 Schlesinger June 30, 1964 3, 139, 338 Do. June 30, 1964 3, 139, 339 Cassiers July 14, 1964 3, 140, 946 Davis et a1 3, 141, 770 Ghys 3,148,982 Oassiers. 3, 155, 503 Do 3,158,475 Tomanek. 3, 161, 505 Schlesinger 3, 163, 530 Do 3, 163,531 Do. 3, 163, 532 Hoegl. 3, 169, 060 Stumpf 3,174, 854 Kluplel et al Apr. 27, 1965.. 3, 180, 729 Do Apr. 27, 1965 3, 180, 730 Neugebauer- June 15, 1965. 3, 189, 447 0 Sept. 14, 1965 3, 206, 306 July 21, 1964 3, 141, 770 June 5, 1962 3, 037, 861 June 26,1962 3,041,165 Schlesinger 3, 066, 023 he 3, 072, 476 Klupfel et al 3, 047, 095 Neugebauer at a 3, 112, 197 Cassiers et al 3, 113, 022 Schlesinger 3, 114, 633 Kosche et a 3, 265, 497 3, 274, 000

The quantity of the above-described dye required to spectrally sensitize an organic photoconductor varies with the results desired, the particular dye used, and the particular organic photoconductor used. Best results are obtained with about .01 to parts by weight dye and about 1 to 75 parts by Weight of the organic photoconductor based on the photoconductive composition. Binder can be employed in such compositions, when desired, at preferred ranges of 25 to 99 parts by Weight. In addition, the composition can contain other sensitizers, either spectral sensitizers or speed increasing compounds, or both.

As used herein and in the appended claims, the terms insulating and electrically conductive have reference to materials the surface resistivities of which are greater than 10 ohms per square unit (e.g., per square foot) and less than 10 ohms per square unit (e.g., per square foot) respectively.

Coating thicknesses of the photoconductive compositions of the invention on a support can vary widely. As a general guide, a dry coating in the range from about 1 to 200 microns is useful for the invention. The preferred range of dry coating thickness is in the range from about 3 to 50 microns.

To produce a reproduction of an image utilizing the electrophotographic elements of our invention, the photoconductive layer is preferably dark adapted, and then is charged either negatively or positively by means of, for example, a corona discharge device maintained at a potential of from 60007000 volts. The charged element is then exposed to light through a master, or by reflex in contact with a master, to obtain an electrostatic image corresponding to the master. This invisible image may then be rendered visible by being developed by contact with a developer including a carrier and toner. The carrier can be, for example, small glass or plastic balls, or iron powder. The toner can be, for example, a pigmented thermoplastic resin having a grain size of from about 1100,u which may be fused to render the image permanent. Alternatively, the developer may contain a pigment or pigmented resin suspended in an insulating liquid which optionally may contain a resin in solution. If the polarity of the charge on the toner particles is opposite to that of the electrostatic latent image on the photoconductive element, a reproduction corresponding to the original is obtained. If, however, the polarity of the toner charge is the same as that of the electrostatic latent image, a reversal or negative of the original is obtained.

Although the development techniques described hereinabove produce a visible image directly on the electrophotographic element, it is also possible to transfer either the electrostatic latent image, or the developed image to a second support which may then be processed to obtain the final print. All of these development techniques are well known in the art and have been described in a number of U.S. and foreign patents.

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

EXAMPLES 1-2 These examples show the great increase in speed of organic photoconductors when the dyes employed in this invention are added thereto. This increase in speed is due to the spectral sensitivity imparted to the photoconductor by the dyes described herein. The examples also show that the maximum sensitivity peaks (Abs. max) occur in most cases at radiations in the region of the spectrum from about 480 to 510 nm. A number of the dyes also impart more than one maximum sensitivity peak as illustrated by Example 1 in Table 1 hereinafter.

A series of solutions are prepared consisting of 5.0 ml. methylene chloride (solvent); 0.15 g. 4,4 bis(diethylamino) 2,2-dimethyltriphenylmethane (organic photoconductor); 0.50 g. polyester composed of terephthalic acid and a glycol mixture comprising a 9:1 weight ratio of 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane and ethylene glycol (binder) and 0.0065 g. of the spectral sensitizing dye indicated by identifying number from above Table A. Each solution is coated on an aluminum surface maintained at 25 C., and dried. All operations are carried out in a darkened room. A sample of each coating is uniformly charged by means of a corona to a potential of about 600 volts and exposed through a transparent member bearing a pattern of varying optical density to a 3000 K. tungsten source. The resultant electrostatic image pattern is then rendered visible by cascading a developer composition comprising finely divided, colored, thermoplastic, electrostatically responsive toner particles carried on glass beads over the surface of the element. The image is then-developed by deposition of the toner in an imagewise manner on the element. (Other development techniques such as those described in U.S. 2,786,- 439; 2,786,440; 2,786,441; 2,811,465; 2,874,063; 2,984,- 163; 3,040,704; 3,117,884; Re. 25,779; 2,297,691; 2,551,- 582; and in RCA Review, vol. 15 (1954) pp. 469-484, can be used with similar results.) An image is formed on each sample, as indicated in Table I. Another sample of each coating is tested to determine its electrical speed and maximum sensitivity peak. This is accomplished by giving each element a positive or negative charge (as indicated in Table I) with a corona source until the surface potential, as measured by an electrometer probe, reaches 600 volts. It is then exposed to light from a 3000 K. tungsten source of 20-foot candles at the exposure surface. The exposure is made through a stepped density gray scale. The exposure causes reduction of the surface potential of the element under each step of the gray scale from its initial potential, V0, to some lower potential, V, whose exact value depends on the actual amount of exposure in metercandle-seconds received by the area. The results of these measurements are plotted on a graph of surface potential V vs. log exposure for each step. The actual speed of each element is expressed in terms of the reciprocal of the exposure required to reduce the surface potential by volts. Hence, the speeds given in Table I are the numerical expression of 10 divided by the exposure in metercandle-seconds required to reduce the 600 volts charged surface potential by 100 volts. The results are shown in Table I below.

Referring to the above Table I, it Will be seen that the control example containing the same photoconductor but no dye shows speeds of only 8 and 7 for the positively and negatively charged surfaces, respectively, whereas, the corresponding values for those of the invention represented by Examples 1 to 2, are clearly of a diiferent order of magnitude. For example, the speed shown by Example 2 (Dye No. (II)) is 310 and 460 for the positively and negatively charged surfaces, respectively, with maximum sensitivity peak at 510 nm., thus indicating a speed increase over that of the control by a factor of about 38 for the positively charged and about 65 for the negatively charged. Also of great significance is the extension of the absolute sensitivity to the region of 500 nm. In the case of Example 1 (Dye No. (1)) the improvement in speed is also impressive in comparison with that of the control by factors of about 25 and 28 for the positively charged and negatively charged surfaces, respectively. Similar results are obtained when Dye (I) or Dye (II) is replaced with any one of Dyes ('III) through (XX), or any dye in the list following Table A.

Similar results to those shown in above Table I are obtained, when, for example, the organic photoconductor 4,4 bis(diethylamino)-2,2'-dimethyltriphenylmethane is replaced with 0.15 g. of triphenylamine (using the p toluenesulfonate salt of each dye), or 1,3,5-triphenyl-2- pyrazoline, or 2,3,4,5-tetraphenylpyrrole, or 4,4'-bis-diethylaminobenzophenone or when other dyes of the invention embraced by Formula I above are used. These results show that the dyes of this invention effectively spectrally sensitize a wide variety of organic photoconductors. The dyes of this invention are not in themselves photoconductive. Also, it should be noted that the above mentioned photoconductors when used alone have very low photoconductive speed to visible light. However, as shown by the tests, the combination of the dyes of the invention with the photoconductors of the invention provide compositions and elements of outstanding speed and excellent quality of image.

This invention is highly unexpected because dyes previously suggested for spectral sensitizers impart weak spectral sensitization to organic photoconductors. Typical dyes proposed by the prior art as spectral sensitizers, which produce weak spectral sensitization in these systems, are shown in Table D below.

TABLE D Dye identification: Name A) Pinacyanol.

(B) Kryptocyanine.

(C) Anhydro-3-ethyl-9 methyl-3'-(3- sulfobutyl thiacarbocyanine hydroxide.

(D) .3,3'-diethyl-9-methy1thiacarbocyanine bromide.

(E) 3-carboxymethyl-5-[(3-methyl-2- thiazolidinylidene) -1-methylethylidene]rhodanine.

(F) Anhydro-S,5'-dichloro-3,9 diethyl- 3'-( 3-sulfobutyl thiacarbocyanine hydroxide.

(G) 1-ethy1-3-methylthia-2'-cyanine chloride.

(H) l,1-diethyl-2,2'-cyanine chloride.

In contrast, the dyes of this invention are desensitizing for conventional negative type photographic silver halide emulsions because they strongly desensitize such emulsions.

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 elfected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

We claim:

1. A composition of matter comprising an organic photoconductor spectrally sensitized with a cyanine dye comprising first and second 5- to 6-membered nitrogen containing heterocyclic nuclei joined together by a methine linkage selected from the group consisting of a dimethine linkage and a trimethine linkage; the first of said nuclei being selected from the group consisting of a pyrrolo [2,3-b]pyrazine nucleus and a pyrrolo[2,3-b1quinoxaline nucleus joined at the 3-carbon atom thereof to said linkage; and said second nucleus being selected from the group consisting of (a) a heterocyclic nitrogen containing nucleus of the type used in cyanine dyes when said linkage is a dimethine linkage; and, (b) when said linkage is a trimethine linkage, said second nucleus is selected from the group consisting of a 2-arylindole nucleus, a pyrrolo [2,3-b1quinoxaline nucleus and a pyrrolo[2,3-b1pyrazine nucleus, each of said nuclei being joined at the 3-carbon atom thereof to said trimethine linkage, to complete said dye.

2. A composition as defined by claim 1 wherein said second nucleus of said dye is an electron-accepting nucleus.

3. A composition as defined by claim 1 wherein said second nucleus of said dye is selected from the group consisting of: a nitro substituted nucleus; an imidazo 1 4 [4,5-b1quinoxaline nucleus; a 1,3,3-trialkyl-3H-pyrro1o [2,3-b1pyridine nucleus; and a 2-arylindole nucleus.

4. A composition as defined by claim 1 wherein said organic photoconductor is selected from the group consisting of: a triarylamine; a 1,3,5--triphenyl-2-pyrazoline; a 4,4'-bis(dialkylamino)-2,2'-dialkyltriarylamine; a 2,3, 4,5-tetraarylpyrrole; and a 4,4'bis-dialkylaminobenzophenone.

5. A composition as defined by claim 1 which comprises from 1 to parts by weight of said photoconductor, said conductor being spectrally sensitized with from 0.1 to 10 parts by weight of said cyanine dye.

6. A composition of matter comprising an organic photoconductor spectrally sensitized with a cyanine dye wherein n represents a positive integer of from 1 to 2; L represents a methine linkage; R represents a member selected from the group consisting of an alkyl group, an alkenyl group and an aryl group; R represents a member selected from the group consisting of an alkyl group and an aryl group; R and R each represents a member selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, and together the nonmetallic atoms necessary to complete a pyrrolo[2,3-b] quinoxaline nucleus; R and R represent a member se lected from the group consisting of a hydrogen atom and an aryl group; R represents a member selected from the group consisting of an alkyl group, an aryl group and a heterocyclic radical containing from S to 6 atoms in the heterocyclic ring and having a hetero nitrogen, oxygen or sulfur atom; X represents an acid anion; D represents the non-metallic atoms necessary to complete a nucleus selected from the group consisting of a 2- arylindole nucleus, a pyrrolo[2,3-b1pyrazine nucleus, and a pyrrolo[2,3-b]quinoxaline nucleus; and Z represents the non-metallic atoms necessary to complete a nitrogen containing heterocyclic nucleus of the type used in cyanine dyes containing from 5 to 6 atoms in the heterocyclic ring.

7. A composition as defined by claim 6 wherein said Z of said dye represents the non-metallic atoms necessary to complete an electron-accepting nucleus.

8. A composition as defined by claim 6 wherein said Z of said dye represents the non-metallic atoms necessary to complete an electron-accepting nucleus selected from the group consisting of a nitrobenzothiazole nucleus, a nitrobenzoxazole nucleus, a nitrobenzoselenazole nucleus, a nitroindole nucleus, an irnidazo[4,5-b]nucleus, and a 1,3,3-trialkyl-3H-pyrrolo-[2,3-b]pyrridine nucleus.

9. A composition as defined by claim 6 wherein said R and R of said dye each represents a hydrogen atom.

10. A composition as defined by claim 6 wherein said R and R of said dye taken together represent the nonmetallic atoms necessary to complete a pyrrolo[2,3-b] quinoxaline nucleus.

15 11. A composition as defined by claim 6 wherein said organic photoconductor has the following formula:

wherein each of D, E and G is an aryl group and J is selected from the group consisting of a hydrogen atom, an alkyl group and an aryl group, at least one of D. E and G containing an amino substituent selected from the group consisting of a secondary amino group and a tertiary amino group.

12. A composition as defined by claim .6 wherein said organic photoconductor is selected from the group consisting of: triphenylamine; 1,3,5-triphenyl-2-pyrazoline; 4,4 bis(diethylamino) 2,2 dimethyltriphenylamine; 2,3,4,5 tetraphenylpyrrole; and, 4,4 bis-diethylaminobenzophenone.

13. A composition as defined by claim 6 which comprises from 1 to 75 parts by weight of said photoconductor, said photoconductor being spectrally sensitized with from .01 to 10 parts by weight of said cyanine dye.

14. A composition as defined by claim 13 wherein said organic photoconductor and said dye are incorporated in an insulating binder.

15. A composition as defined by claim 13 wherein said organic photoconductor and said dye are dispersed is from 25 to 99 parts by weight of a polyester of terephthalic acid and a glycol mixture consisting of a 9:1 weight ratio of 2,2'-bis [4-(2-hydroxyethoxy)phenyl] propane and ethylene glycol as insulating binder.

16. A composition of matter comprising from 1 to 75 parts by weight of an organic photoconductor selected from the group consisting of: triphenylamine; 1,3,5-triphenyl 2 pyrazoline; 4,4 bis diethylamino 2,2- dimethyltriphenylmethane; 2,3,4,5 tetraphenylpyrrole; 4,4 bis diethylaminobenzophenone; said organic photoconductor being spectrally sensitized with from .01 to 10 parts by weight of a dye selected from the group consisting of 1,3 diethyl 6 nitro 3 pyrrolo[2,3-b] quinoxalinothiacarbocyanine salt and 1,3 diallyl 1'- ethylimidazo [4,5-b1quinoxalino 3 pyrrolo[2,3-b] quinoxalinocarbocyanine salt.

17. A composition of matter as defined in claim 16 wherein said organic photoconductor and said dye are dispersed in from 25 to 99 parts by weight of a polyester of terephthalic acid and a glycol mixture consisting of a 9:1 weight ratio of 2,2 bis [4-(2-hydroxyethoxy) phenyl]propane and ethylene glycol as insulating binder.

18. An electrophotographic element comprising a conductive support having thereon a layer comprising an organic photoconductor in an insulating binder, said organic photoconductor being spectrally sensitized with a cyanine dye selected from those comprising first and second 5- to 6-membered nitrogen containing heterocyclic nuclei joined together by a methine linkage selected from the group consisting of a dimethine linkage and a trimethine linkage; the first of said nulei being selected from the group consisting of a pyrrolo[2,3-b]-pyrazine nucleus and a pyrrolo[2,3-b]quinoxaline nucleus joined at the 3-carbon atom thereof to said linkage; and said second nucleus being selected from the group consisting of (a) a heterocyclic nitrogen containing nucleus of the type used in cyanine dyes when said linkage is a dimethine linkage; and (b) when said linkage is a trimethine linkage, said second nucleus is selected from the group consisting of a 2-arylindole nucleus, a pyrrolo[2,3-b1quinoxaline nucleus and a pyrrole[2,3-b]pyrazine nucleus, each of said nuclei being joined at the 3-carbon atom thereof to said trimethine linkage, to complete said dye.

19. An electrophotographic element as defined in claim 18 wherein said second nucleus of said dye is selected from the group consisting of: a nitro substituted nucleus; an imidazo[4,5-b]quinoxa1ine nucleus; a 1,3,3-

16 trialkyl-S'H-pyrrolo[2,3-b1pyridine nucleus; and, a 2-arylindole nucleus.

20. An electrophotographic element as defined in claim 18 wherein said Organic photoconductor is selected from the group consisting of: a triphenylamine; a 1,3,5-triaryl-2-pyrazoline; a 4,4'-bis-(dialkylamino)-2,2'-dialkyltriarylamine; a 2,3,4,5-tetraarylpyrrole; and a 4,4'-bisdialkylaminobenzophenone.

21. An electrophotographic element as defined in claim 18 wherein said layer comprises from 1 to parts by weight of said photoconductor, said photoconductor being spectrally sensitized with from .01 to 10 parts by weight of said cyanine dye.

22. An electrophotographic element comprising a con ductive support having thereon a layer comprising an organic photoconductor spectrally sensitized with a dye selected from those represented by the following formulas:

wherein n represents a positive integer of from 1 to 2; L represents a methine linkage; R represents a member selected from the group consisting of an alkyl group, an alkenyl group and an aryl group; -R represents a member selected from the group consisting of an alkyl group and an aryl group; R and R each represent a member selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, and together the nonmetallic atoms necessary to complete a pyrrolo[2,3-b] quinoxaline nucleus; R and R represent a member se lected from the group consisting of a hydrogen atom and an aryl group; R represents a member selected from the group consisting of an alkyl group, an aryl group and a heterocyclic radical containing from 5 to 6 atoms in the heterocyclic ring and having a heteronitrogen, oxygen or sulfur atom; X represents an acid anion; D represents the non-metallic atoms necessary to complete a nucleus selected from the group consisting of a 2-arylindole nucleus, a pyrrolo[2,3-b]pyrazine nucleus and a pyrro1o[2,3-b]quinoxaline nucleus; and Z represents the non-metallic atoms necessary to complete a nitrogen containing heterocyclic nucleus of the type used in cyanine dyes containing from 5 to 6 atoms in the heterocyclic ring.

23. An electrophotographic element as defined in claim 22 wherein said Z of said dye represents the non-metallic atoms required to complete an electron-accepting nucleus.

24. An electrophotographic element as defined in claim 22 wherein said Z represents the non-metallic atoms required to complete an electron-accepting nucleus selected from the group consisting of a nitrobenzothiazole nucleus, a nitrobenzoxazole nucleus, a nitrobenzoselenazole nucleus, a nitroindole nucleus, an imidaz0[4,5-b]quinox aline nucleus, and a 1,3,3-trialkyl-3H-pyrrolo[2,3-b] pyridine nucleus.

25. An electrophotographic element as defined in claim 22 wherein said R and R of said dye each represents a hydrogen atom.

26. An electrophotographic element as defined in claim 22 wherein said R and R of said dye taken together represent the non-metallic atoms necessary to complete a pyrrolo[2,3-b]quinoxaline nucleus.

27. An electrophotographic element as defined in claim 22 wherein said organic photoconductor has the following formula:

wherein each of D, E and G is an aryl group and J is selected from the group consisting of a hydrogen atom, an alkyl group and an aryl group, at least one of D, E and G containing an amino substituent selected from the group consisting of a secondary amino group and a tertiary amino group.

28. An electrophotographic element as defined in claim 22 wherein said organic photoconductor is selected from the group consisting of: triphenylamine; 1,3,5-triphenyl- 2 pyrazoline; 4,4'-bis-(diethylamino)-2,2-dimethyltriphenylarnine; 2,3,4-5-tetraphenylpyrrole; and 4,4'-bis-diethylaminobenzophenone.

29. An electrophotographie element as defined in claim 22 wherein said layer comprises from 1 to 75 parts by weight of said photoconductor, said photoconductor being spectrally sensitized with from .01 to parts by weight of said cyanine dye.

30. An electrophotographic element as defined in claim 29 wherein said organic photoconductor and said dye are incorporated in an insulating binder.

31. An electrophotographic element as defined in claim 30 wherein said organic photoconductor and said dye are dispersed in from 25 to 99 parts by weight of a polyester of terephthalic acid and a glycol mixture consisting of 9:1 weight ratio of 2,2-bis-[4-(2-hydroxyethoxy)- phenyl]-propane and ethylene glycol as insulating binder.

32. An electrophotographic element comprising a conductive support having thereon a. layer comprising from 1 to parts by weight of an organic photoconductor selected from the group consisting of: triphenylamine; 1,3,5-triphenyl-2-pyrazoline; 4,4-FDis-diethylamino-2,2'-dimethyltriphenylmethane; 2,3,4,5-tetraphenylpyrrole; 4,4- bis-diethylaminobenzophenone; said organic photoconductor being spectrally sensitized with from .01 to 10 parts by weight of a dye selected from the group consisting of 1,3 diethyl-6'-nitro3-pyrrolo[2,3-b]quinoxalinothiacarbocyanine salt and 1,3-diallyl-1-ethylimidazo- [3,4-b]quinoxalino 3 pyrrolo [2,3-b]quinoxalinocarbocyanine salt.

33. An electrophotographic element as defined in claim 32 wherein said organic photoconductor and said dye are dispersed in from 25 to 99 parts by Weight of a polyester of terephthalic acid and a glycol mixture consisting of a 9:1 weight ratio of 2,2-bis-[4-(2-hydroxyethoxy)-phenyl]-propane and ethylene glycol as insulating binder.

References Cited UNITED STATES PATENTS 2,927,026 3/ 1960 Heseltine et al. 96105 3,132,942 5/1964 Stewart 961 3,143,544 8/1964 Van Dormael 260-240 3,314,796 4/1967 Gotze et al. 96101 3,326,688 6/1967 Jenkins et al. 96102 3,455,684 7/1969 Depoorter et al. 961.7 3,468,661 9/ 1969 Libeer et al. 96-1.7

GEORGE F. LESMES, Primary Examiner M. B. WITTENBERG, Assistant Examiner US. Cl. X.R.