EP0058839A1

EP0058839A1 - Sensitized organic electron donor compounds

Info

Publication number: EP0058839A1
Application number: EP82100686A
Authority: EP
Inventors: Louis M. Leichter; John J. Stofko, Jr.; Terry J. Sonnonstine; Paolo Beretta
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1981-02-23
Filing date: 1982-02-01
Publication date: 1982-09-01
Also published as: DE3270544D1; EP0058839B1

Abstract

Organic electron donor compounds for use in electrophotographic constructions must ordinarily be sensitized to desired regions of the electromagnetic spectrum. Dyes selected from the group of 1) highly fluorinated aliphatic sulfonyl, carbonyl, or caronyloxy dyes, 2) imidazo[4,5-b] quinoxaline cyanine dyes having phenyl- sulfonyl or benzoyl substituents and 3) indolenine dyes having phenylsulfonyl or benzoyl substituents thereon have been found to be efficient sensitizers for such organic donor compounds.

Description

TECHNICAL FIELD

The present invention relates to novel photoconductive layers which comprise organic electron donor compounds and sensitizer dyes selected from the group consisting of 1) phenylsulfonyl or benzoyl substituted imidazo-[4,5-b]-quinoxaline dyes, 2) phenylsulfonyl or benzoyl substituted indolenine dyes, and 3) highly fluorinated aliphatic sulfonyl sensitizer dyes. These layers are particularly useful in imaging systems such as electrophotography or electroradiography.

BACKGROUND OF THE ART

The technology of electrophotography is commercially well established. A wide variety of processes and apparatus are used, although they have many characteristics in common. One of the more common forms of this technology involves the use of a plate having a photoconductive insulating layer, generally coated on a conductive layer. Imaging is effected by first uniformly electrostatically charging the surface of the photoconductive layer and then exposing the charged layer to an image or pattern of activating electromagnetic radiation, usually visible light or ultraviolet radiation. This exposure selectively enables the charge in the irradiated areas of the photoconductive insulator to dissipate. The charge which remains in the non-irradiated areas forms a latent image which may be further processed to form a more permanent record of the exposing image or pattern. The most common form of additional processing involves the attraction of particles of material selectively to the charged areas and fusing them to the photoconductive layer or transferring the particles in their imagewise distribution to another surface to which they are more permanently bound by an adhesive or by fusion of the particles themselves. A common electrophotographic construction comprises, in sequence, a substrate, a conductive layer, and a photoconductive insulating layer.
Typical classes of photoconductive materials useful in electrophotography include 1) inorganic crystalline photoconductors such as cadmium sulfide, cadmium sulfoselenide, cadmium selenide, zinc sulfide, zinc oxide, and mixtures thereof, 2) inorganic photoconductive glasses such as amorphous selenium, selenium alloys, and selenium-arsenic, and 3) organic photoconductors such as phthalocyanine pigments and polyvinyl carbazole, with or without binders and additives which extend their range of spectral sensitivity. These systems are well known in the art. For example, U.S. Patent No. 3,877,935 discusses various problems associated with the crystalline and amorphous classes of photoconductors and shows the use of polynuclear quinone pigments in a binder as a photoconductive layer. U.S. Patent No. 3,824,099 shows the use of squaric acid methine sensitizing dyes and triaryl pyrazoline charge transport materials as an electrophotographic construction. Cadmium sulfoselenide plates are shown in U.S. Patent No. 3,764,315, and one of the original disclosures of the use of poly-N-vinylcarbazole as a photoconductive insulating layer is provided in U.S. Patent No. 3,037,861. A number of diverse organic photoconductors have been disclosed since the development of the carbazole class of photoconductors such as quinones and anthrones (e.g., Hayashi et al., Bull. Chem. Soc. Japan, vol. 39, (1966) pp. 1670-1673), but the carbazoles have continued to attract the greatest attention.
Problems particularly associated with the use of carbazoles as a positive charge transporting material which is capable of supporting the injection of photoexcited holes from a photoconductive layer and is capable of transporting the injected holes also exist in this area of technology. The carbazole condensates with aldehydes as shown in U.S. Patent No. 4,025,341 have a tendency to oligomerize. This oligomerization can cause a number of problems. The oligomers formed are not of a uniform molecular weight and carbazole content. This creates problems in purification and can create undesirable variations in photoconductive or charge transport properties. Triaryl methanes including a carbazole moiety (as shown in Xerox Disclosure Journal, Vol. 3, No. 1, Jan/Feb 1978, page 7) also tend to be sensitive to oxidation which converts them to an ionic species which will not act as a photoconductive insulator but rather will act as a conductor.
Japanese Patent Publication 52-34735 discloses carbazole organic photoconductor materials which may have substituents thereon which would inherently prevent oligomerization of the carbazoles. This is not recognized in the disclosure and the carbazoles would still be subject to oxidation problems.

SUMMARY OF THE INVENTION

Electronically active organic donor compounds have been found to be sensitized by phenylsulfonyl or benzoyl substituted imidazo-[4,5-b]-quinoxaline cyanine dyes.
A novel class of electronically active organic donor compounds particularly useful in the present invention has the formula:
where X is
wherein R is an aliphatic, aromatic, or mixed aliphatic-aromatic group and Y is an aliphatic, aromatic, heterocyclic, or mixed aliphatic-aromatic group. For example, R and Y may be independently selected from alkyl groups, benzyl groups, phenyl groups, naphthyl groups, anthracyl groups, etc., with such various substituents as alkoxy groups, amine groups, alkyl groups, hydroxyl groups, and halogen atoms thereon.
These compounds have been found to be electron donor compounds and are useful in forming photoconductive layers when sensitized with cyanine dyes having an imidazo-[4,5-b]quinoxaline nucleus. They may be combined with polymeric binder materials to form photoconductive layers which are solid state molecular solution charge transport layers. The electron donor compounds have a reduced sensitivity to oxidation and oligomerization.

DETAILED DESCRIPTION OF THE INVENTION

All electronically active organic donor compounds, as they are known in the art, may be sensitized to various portions of the electromagnetic spectrum by sensitizing dyes selected from the group consisting of 1) imidazo-[4,5-b]-quinoxaline cyanine dyes, 2) phenyl- sulfonyl or benzoyl substituted indolenine dyes and 3) highly fluorinated aliphatic sulfonyl sensitizer dyes. Typical electronically active organic electron donor compounds are poly-N-vinylcarbazole, polyanthracene, oxadiazoles, pyrazolines, poly(vinyl acenaphthalene), poly-2,9-methylene fluorene, polyvinyl ferrocene, polybenzocarbazole, polybenzoanthracene, and the like.
Novel electronically active organic donor compounds useful in the practice of the present invention are bis (benzocarbazoles)trisubstitutedmethanes which may be represented by the formula
wherein X is
wherein R is an aliphatic, aromatic or mixed aliphatic-aromatic group and
Y is an aliphatic, aromatic, heterocyclic or mixed aliphatic-aromatic group.
All of the compounds of the present invention may be synthesized by reactkng the appropriate N-substituted benzo[a]carbazole or benzo[b]carbazole:
with the correspondingly appropriate aldehyde:
This process can be carried out in a solvent (e.g., ethanol) in the presence of an acid (e.g., HC1) catalyst. The reaction product may be isolated by simple filtration and washing. For example, in the reaction of 11-ethylbenzo[a]carbazole with benzaldehyde in ethanol in the presence of HC1 as a catalyst, the preferential reaction of the aldehyde at the 5-position of the 11-benzo[a]carbazole and the insolubility of the reaction product:
in ethanol, no oligomeric species are formed such as occur in a similar reaction with N-ethyl-carbazole. The reaction product is also stabilized against oxidation of the methine group by the rings ortho to point at which the methine group is bonded to the benzocarbazole nucleus.
R may, as previously stated, be selected from aliphatic, aromatic and mixed aliphatic-aromatic groups. These groups may or may not be substituted. If they are substituted, it would be preferred that they be electron donating substituents although election withdrawing substituents may be tolerated. Preferably R is selected from alkyl groups of 1 to 20 carbon atoms, preferably n-alkyl groups of 2 to 20 carbon atoms, aryl groups such as phenyl or naphthyl groups, with phenyl groups preferred, alkaryl groups, for example benzyl groups, and allyl groups. Where the term 'group' is used anywhere in the practice of the present invention, as opposed to the term 'radical', the possibility of substitution is specifically intended to be included within the definition of that term. For example, n-alkyl radical may be only.of the formula -(CH₂)_n-CH₃ while n-alkyl group may have hydrogen atoms on the n-alkyl radical substituted with other moieties such as halogen atoms, hydroxyl radicals, alkoxy radicals, alkyl radicals, amine radicals, cyano radicals, etc. Specific examples of useful R moieties are ethyl, n-butyl, n-propyl, 4-methoxybutyl, 3-chloropropyl, 8-hydroxyoctyl, phenyl, benzyl, allyl, p-ethylphenyl, m-tert-butylnaphthyl, p-diethylaminophenyl, stearyl, dodecyl, etc. R preferably has fewer than 20 carbon atoms, but may have up to 30 or more carbon atoms. The main influence of this group, except where electronic induction occurs because of a change of the nature of this group, is in the solubility of the compound.
Y may, as previously-stated, be selected from aliphatic, aromatic, and mixed aliphatic-aromatic groups. These groups may or may not be substituted. Examples of useful moieties are methyl, ethyl, n-pentyl, nonyl, stearyl, tolyl, anisyl (m-, p-, and o-), p-chlorobenzyl, o-bromobenzyl, p-hydroxybenzyl, veratryl, isobutyl, terphthalyl, p-octyloxybenzyl, p-dimethylaminophenyl, t-butyl, etc. Preferred Y moieties are phenyl, tolyl, anisyl, and benzyl groups because of their availability. As with group R, the main influence of this group; except with regard to electron induction effects, is on the solubility of the compounds. Preferably Y has 20 or fewer carbon atoms, but up to 30 may be readily tolerated.
The imidazo-[4,5-b]quinoxaline cyanine sensitizers which are a part of the present invention are disclosed in British Patent No. 1,555,053. This reference teaches cyanine dyes in silver halide emulsions or photoconductive binders as sensitizer dyes.
The dyes may be represented by the formulae described in British Patent 1,555,053 which reference is incorporated herein in its entirety, and preferred dyes by the formulae:
wherein W represents:

(this formula being a particular case of formula I)

wherein g represents a positive integer of from 1 to 3 (preferably 1 to 2), and r represents a positive integer of from 1 to 2, R and R₁ each represents a substituent independently selected from the group consisting of an acyclic hydrocarbon substituent, such as an alkyl group (including substituted alkyl), preferably containing from 1 to 13 carbon atoms, e.g. methyl, ethyl,. propyl, isopropyl, butyl, sec-butyl, hexyl, cyclohexyl, dodecyl, octadecyl, hydroxyalkyl (e.g. ω-hydroxyethyl, ω-hydroxypropyl, etc.), and alkenyl substituents, such as allyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl and 3-butenyl, etc.; alkaryl substituents such as benzyl and ω-phenylethyl; and aryl substituents, e.g., phenyl, p-tolyl, o-tolyl, 3,4-dichlorophenyl, etc., groups; R₂ represents a 6- or 7-position substituent selected from phenylsulfonyl or benzoyl; X- represents an acid anion such as for example, in order of general preference perchlorate, tetrafluoroborate, p-toluenesulfonate, methylsulfate, sulfamate, iodide, bromide, and chloride; R₃ represents a substituted or non-substituted aliphatic group such as an alkyl group of from 1-12 carbon atoms, e.g., methyl, Y-sulfopropyl, isopropyl, butyl, sec-butyl, w-sulfobutyl, dodecyl, β-hydroxyethyl, γ-hydroxypropyl, β-methoxyethyl, a-ethoxy-ethyl, allyl, benzyl, β-phenylethyl, β-carboxyethyl, carboxymethyl, γ-carboxypropyl, S-acetoxyethyl, γ-acetoxypropyi, carbomethoxymethyl, carboxyethoxyethyl, etc., groups; R₄ and R₅ each represents the same or different alkyl group of from 1-6 carbon atoms, e.g., methyl, ethyl, 2-cyanoethyl, propyl, isopropyl, butyl, hexyl, etc., groups, X represents any anion such as an acid ion, e.g., chloride, bromide, iodide, thiocyanate, sulfamate, methyl sulfate, ethyl sulfate, perchlorate, p-toluenesulfonate, etc., Z represents the non-metallic atoms required to complete a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, which may also include, in addition to the hetero nitrogen atom, a second hetero atom such as an oxygen atom, a sulfur atom, a selenium atom, or a second nitrogen atom, such as the atoms required to complete a thiazole nucleus; a benzothiazole nucleus; a naphthothiazole nucleus; a thianaphtheno-7',6', 4,5-thiazole nucleus; an oxazole nucleus; a benzoxazole nucleus; a naphthoxazole nucleus; a selenazole nucleus; a benzoselenazole nucleus; a naphthoselenazole nucleus; a thiazoline nucleus; a 2-quinoline nucleus; a 4-quinoline nucleus; a 1-isoquinoline nucleus; a 3-isoquinoline nucleus; a 3,3-dialkylindolenine nucleus; a 2-pyridine nucleus; a 4-pyridine nucleus; a 1-alkylimidazole nucleus; a 1-alkylbenzimidazole nucleus; and a 1-alkylnaphthimidazole nucleus; and, Q represents the non-metallic atoms required to complete a 5 to 6 membered heterocyclic nucleus, typically containing a hetero atom selected from nitrogen, sulfur, selenium, and oxygen, such as a 2-pyrazolin-5-one nucleus; an isoxazolone nucleus; an oxindole nucleus; a pyrimidine nucleus; a rhodanine nucleus; a 2(3H)-imidazo-[l,2-a]-pyridone nucleus; a 5,7-dioxo-6, 7-dihydro-5-thiazolo[3,2-a]-pyrimidine nucleus; a 2-thio-2,4-oxazolidinedione nucleus; a thianaphthenone nucleus; a 2-thio-2,5-thiazolidinedione nucleus; a 2,4-thiazolidinedione nucleus; a thiazolidinone nucleus; a 2-thiazolin-4-one series; a 2-imino-4-oxazolidinone (i.e., pseudohydantoin) nucleus; a 2,4-imidazolidinedione (hydantoin) series; a 2-thio-2,4-imidazolidinedione (i.e., 2-thiohydantoin) nucleus; a 2-imidazolin-5-one nucleus, etc. (especially useful are nuclei wherein Q represents a heterocyclic nucleus containing 5 atoms in the heterocyclic ring., 3 of said atoms being carbon atoms, 1 of said atoms being a nitrogen atom, and 1 of said atoms being selected- from the group consisting of a nitrogen atom, an oxygen atom, and a sulfur atom).
L represents a cation nucleus of l-alkyl-2-phenylindol-3-yl, l-aryl-2-phenylindol-3-yl, 1-alkyl or aryl-2-phenyl-5-nitro-indol-3-yl, l-alkyl-2-phenyl-5-phenylsulfonylindol-3-yl, l-aryl-2-phenyl-5-phenylsul- fonylindol-3-yl, l-aryl-2-phenyl-5-phenylsulfonylindol-3-yl, 1-alkyl-2-phenyl-5-benzoylindol-3-yl, l-aryl-2-phenyl-5-benzoylindol-3-yl, 9-methyl-carbazol-3-yl, 2-alkyl or substituted alkyl-3-phenyl-5-oxo-3-iso- oxazolin-4-yl, 2-alkyl or substituted alkyl-3-furyl-5-oxo-3-isoxazolin-4-yl, 2-alkyl or substituted alkyl-3-thienyl-5-oxo-3-isoxazolin-4-yl, 2-alkyl or substituted 3-pyrryl-5-oxo-3-isoxazolin-4-yl, l-aryl-3,5-dialkyl- pyrazol-4-yl series.
Surprisingly the counterion (the acid anion, X-) has been found to significantly affect the sensitizing ability of the dyes according to the present invention. The reason for this is not understood. The general order of preference for the anions is perchlorate (most preferred), tetrafluoroborate, p-toluenesulfonate, methylsulfate, sulfamate, iodide, bromide, and chloride.
With regard to the above mentioned substituent groups (^{i.e., R, R}1, R₂, R₃, R₄, R₅, Z, Q, L and X-) the size of such groups is not believed to be of any substantial significance in the practice of this invention. Size changes may only require modification of solvents necessary to include them in photosensitive systems, but the action of these dyes is believed to be substantially the same, without regard to size. However, for purposes of economics, the following moiety sizes are generally preferred. The second nucleus (heterocyclic or paraamino- phenyl) should contain no more than 50 carbon atoms and no more than 10 non-metallic heteroatoms such as nitrogen, sulfur and oxygen (metal atoms may appear in these groups only in the form of salts). It is more preferred that such second nucleus contains no more than 30 carbon atoms and most preferred no more than 20 carbon atoms. For groups R and R₁ it is generally preferred to have no more than 18 carbon atoms and most preferred to have no more than 10 carbon atoms. For group R₂ (when benzoyl and phenyl-sulfonyl) the generally preferred aryl groups of this invention are phenyl and naphthyl and derivatives thereof. R₄ and R₅ are preferred to have no more than 6 carbon atoms each. None of R₂, R₄ and R₅ should contain metal atoms.
The preferred dyes of this class are those of U.K. Patent No. 1,555,053 in which the imidazo-[4,5-b]-quinoxaline cyanine dye bears a 5-phenylsulfonyl or 5-benzoyl substituent.
The indolenine sensitizers which are a part of the present invention are disclosed in U.S. Patent No. 4,025,347. This reference teaches the use of the indolenine dyes in silver halide emulsions as sensitizer dyes.
The dyes may be represented by the formulae:

and
wherein A is selected from
and
B is selected from
and
n represents a positive integer of from 1 to 4, m and q each represents a positive integer of from 1 to 2, p represents a positive integer of from 1 to 3, r is 0 or 1, R₂ represents a substituent independently selected from the group consisting of an acyclic hydrocarbon substituent (substituted or not), preferably aliphatic, such as an alkyl group (including substituted alkyl), preferably containing from 1 to 13 carbon atoms, e.g. methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, hexyl, cyclohexyl, dodecyl, octadecyl, hydroxyalkyl (e.g. ω-hydroxyethyl, ω-hydroxypropyl, etc.), and alkenyl substituents, such as allyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl and 3-butenyl, etc.; alkaryl substituents such as benzyl and β-phenylethyl; and aryl substituents, e.g., phenyl, p-tolyl, o-tolyl, 3_r4-dichlorophenyl, etc., groups; R₁ represents a 5-position substituent selected from phenylsulfonyl or benzoyl; X- represents an acid anion such as for example, in order of general preference perchlorate, tetrafluoroborate, p-toluenesulfonate, methylsulfate, sulfamate, iodide, bromide, and chloride; R₃ and R₄ represents a substituted or non-substituted aliphatic group such as an alkyl group of from 1-12 carbon atoms, e.g., methyl, γ-sulfopropyl, isopropyl, butyl, sec-butyl, ω-sulfobutyl, dodecyl, β-hydroxyethyl, y-hydroxypropyl, β-methoxyethyl, β-ethoxy-ethyl, allyl, benzyl, β-phenylethyl, S-carboxyethyl, carboxymethyl, Y-carboxypropyl, β-acetoxyethyl, γ-acetoxypropyl, carbomethoxymethyl, carboxyethoxyethyl, etc., groups; R₅ and R₆ each represents the same or different alkyl group of from 1-6 carbon atoms, e.g., methyl, ethyl, 2-cyanoethyl, propyl, isopropyl, butyl, hexyl, etc., groups, X represents any anion such as an acid ion, e.g., chloride, bromide, iodide, thiocyanate, sulfamate, methyl sulfate, ethyl sulfate, perchlorate, p-toluenesulfonate, etc., _R ⁷ is selected from the group of hydrogen, halogen (particularly chloro and bromo), cyano, alkyl (preferably with no more than 4 carbon atoms, although longer chains may prevent increased solubility in certain materials), alkoxy (preferably with no more than 4 carbon atoms), phenoxy, aryl (e.g., phenyl, naphthyl, thienyl, tolyl), amino (e.g., NH₂, methylamino, diethylamino, phenylamino, methylphenylamino), thiophenyl, thioalkyl (preferably with no more than 4 carbon atoms), and the like, the chloro substituent being preferred; Z represents the non-metallic atoms required to complete a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, which may also include, in addition to the hetero nitrogen atom, a second hetero atom such as an oxygen atom, a sulfur atom, a selenium atom, or a second nitrogen atom, such as the atoms required to complete a thiazole nucleus or benzothiazole nucleus; a naphthothiazole nucleus; a thianaphtheno-7',6', 4,5-thiazole nucleus; an oxazole nucleus; a benzoxazole nucleus; a naphthoxazole nucleus; a selenazole nucleus; a benzoselenazole nucleus; a naphthoselenazole nucleus; a thiazoline nucleus; a 2-quinoline nucleus; a 4-quinoline nucleus; a 1-isoquinoline nucleus; a 3-isoquinoline nucleus; a 3,3-dialkylindolenine nucleus; a 2-pyridine nucleus; a 4-pyridine nucleus; a 1-alkylimidazole nucleus; a 1-alkylbenzimidazole nucleus; and a 1-alkyl-naphthimidazole nucleus; and, Q represents the non-metallic atoms required to complete a 5 to 6 membered heterocyclic nucleus, typically containing a hetero atom selected from nitrogen, sulfur, selenium, and oxygen, such as a 2-pyrazolin-5-one nucleus; an isoxazolone nucleus; an oxindole nucleus; a pyrimidine nucleus; a rhodanine nucleus; a 2(3H)-imidazo-[1,2-a]-pyridone nucleus; a 5,7-dioxo-6, 7-dihydro-5-thiazolo[3,2-1]-pyrimidine nucleus; a 2-thio-2,4-oxazolidinedione nucleus; a thianaphthenone nucleus; a 2-thio-2,5-thiazolidine-dione nucleus; a 2,4-thiazolidinedione nucleus; a thiazolidinone nucleus; a 2-thiazolin-4-one series; a 2-imino-4-oxazolidinone (i.e., pseudohydantoin) nucleus; a 2,4-imidazolidinedione (hydantoin) series; a 2-thio-2,4-imidazolidinedione (i.e., 2-thiohydantoin) nucleus; a 2-imidazolin-5-one nucleus, etc. (especially useful are nuclei wherein Q represents a heterocyclic nucleus containing 5 atoms in the heterocyclic ring, 3 of said atoms being carbon atoms, 1 of said atoms being a nitrogen atom, and 1 of said atoms being selected from the group consisting of a nitrogen atom, an oxygen atom, and a sulfur atom).
Surprisingly the counterion (the acid anion, X-) has been found to significantly affect the sensitizing ability of the dyes according to the present invention. The reason for this is not understood. The general order of preference for the anions is perchlorate (most preferred), tetrafluoroborate, p-toluenesulfonate, methylsulfate, sulfamate, iodide, bromide, and chloride.
The preferred dyes are those of U.S. Patent No. 4,025,347 in which the indolenine portion of the dye bears a 5-phenylsulfonyl or 5-benzoyl substituent.
The disulfone dyes used in the practice of the present invention are themselves well known in the art for use in light filters, photographic elements, and textiles. These dyes are shown, for example, in U.S. Patents Nos. 3,933,914 and 4,018,810. These dyes may be generally described by the formula:
wherein R_a represents a monovalent chromophoric radical, M represents
or
R_f represents a highly fluorinated aliphatic radical, and R represents a monovalent electron-withdrawing radical. These R groups may include such materials as a cyano, arylcarbonyl, alkylcarbonyl, perfuoralkyl, alkylsulfonyl, highly fluorinated alkylsulfonyl, perfluoroalkylsulfonyl, arylsulfonyl, nitro, sulfonyl floride, or sufonyl chloride radical. Radicals preferred for R include cyano, highly fluorinatd aliphaticsulfonyl, fluoroalkylsulfonyl or highly fluorinated alkylcarbonyloxy (for example having from 1-18 carbon atoms - preferably 1-8 carbon atoms), and arylsulfonyl (preferably phenylsulfonyl). The term highly fluorinated aliphatic radical is defined in the present invention as an aliphatic group having its carbon atoms fluorinated except that with two or more carbon atoms present in the group, the terminal carbon atom may have a hydrogen or chloro substituent, and with four or more carbon atoms the last two carbon atoms may have one or two hydrogen or chlorine subsituents.
The preferred chromophoric radicals that are repreesnted by R_a in the general formula are radicals having chemical structures shown in Formulae II-V as follows:
wherein R₅ and R₂ are hydrogen, monovalent alkyl of 1 to 20 carbon atoms (preferably methyl or ethyl), cyanoaklyl (preferably cyanomethyl or cyanoethyl), aryl (preferably phenyl), or aralkyl (preferably benzyl); n is the integer 0, 1, or 2, X is halogen (preferably chlorine or bromine), lower alkyl (e.g., having 1-3 carbon atoms), cyano, nitro, lower alkoxy (preferably having 1-3 carbon atoms), hydrogen, hydroxyl, sulfonate, or carboxyl; and m is the integer 1-3;
wherein X is as defined above, A is a trivalent alkenylene radical having from 2-4 carbon atoms, and Q is a divalent nitrogen atom, substituted nitrogen (e.g., with such as a hydrogen, alkyl or aryl (e.g., phenyl)), or a divalent oxygen;
wherein R₃ is an alkyl group having from 1-4 carbon atoms, b is the integer 1-5 and Ar is a naphthylene group having a valency of b+l; and
wherein X is as defined above, c is the integer 1, 2, or 3, and R₄ is hydrogen, alkoxy, or a monovalent alkyl group (preferably having from 1-3 carbon atoms).
_Rf is preferably a saturated fluoroaliphatic radical, for example containing 1 to 18 carbon atoms (preferably 1 to 8 carbon atoms) with the majority of the carbon atoms most preferably being perfluorinated.
The term "perfluorinated" is employed to denote substitution of all carbon-bonded hydrogen atoms by fluorine atoms, in accord with the recognized usage of the term.
The above mentioned highly fluorinated aliphatic groups are defined as aliphatic groups which can contain chlorine and hydrogen atoms bonded to the carbon atoms (not more than one chlorine or hydrogen for two adjacent carbons) as well as having fluorine atoms bonded to carbon atom. The fluoroaliphatic radical may be a straight or branched chain, cyclic, or a straight chain including a cyclic portion. Additionally, the fluoroliphatic group may contain an oxygen atom linking two carbon atoms, e.g., -CF₂0CF₂-₁ or a nitrogen atom linking three carbon atoms, e.g., (R_fCH₂)₂NCF₂-. Exemplary aliphatic groups include 1,1,1-tris-trifluoroethyl,-perfluoromethyl, perfluorobutyl, perfluorooctyl, perfluorododecyl, perfluoroisopropyl, perfluoro-(2-cyclohexylethyl), omega-chloroperfluorohexyl, 2-hydroperfluoropropyl, perfluoro(3- morpholinopropyl), and perfluoro(3-piperidinopropyl).
The preparation of these dyes is clearly described in the above cited U.S. Patents.
Various binder materials known in the art are useful with the electronically active electron donor compounds of the present invention. It is of course preferred that the binder be essentially optically transparent or at least transparent to the wavelengths of radiation to which the compounds (sensitized or not) are sensitive. Amongst the useful binders are poly(vinyl chloride), poly(siloxanes), poly(vinyl butyral), poly(vinyl acetate), styrene/acrylonitrile copolymers, polyacrylates, polymethacrylates, polycarbonates, polyepoxides,. polyurethanes, polyamides, polyethers, polyesters, polyolefins as well as block, graft, random, and alternating polymers, copolymers, terpolymers and mixtures thereof and the like. The binders are preferably electrically inactive themselves. The preferred polymeric binders are polycarbonates, polyesters, and styrene/ acrylonitrile copolymers. Coating aids, lubricants, surface active agents, and other adjuvants may be added to the composition.
For use of the materials of the present invention as electrophotographic layers, the organic electron donor compounds should be present as at least 20 percent by weight of the composition. Preferably the donor compound should be present as at least 25 or 35 percent by weight of the layer, and may comprise up to 100% by weight of the layer, excluding of course the sensitizer dye. The sensitizing dyes should be used in amounts which will increase the sensitivity of the composition. This is defined as an effective sensitizing amount of dye. Ordinarily amounts of up to 10% by weight dye may be used, but certain constructions can be envisaged with as much as 90% by weight of dye and 10_% by weight of organic electron donor compounds. Amounts of dye as small as 0.005 percent by weight can be useful. More preferred concentration ranges are between 0.05 and 5 percent by weight.
The photosensitive materials of the present invention may also be useful as photoconductive toners, photovoltaic devices, organic semiconductors, and the like, and may use concentrations of organic electron donor compounds as low as 5 percent by weight.
It has been surprisingly noted that the benzocarbazole-aldehyde condensation products useful in the present invention are better charge transport materials than the corresponding benzocarbazoles by themselves. This is susprising because it is the benzocarbazole nucleus which is the electronically active portion of both molecules. Even when benzocarbazoles were used in reasonably higher molecular proportions to the binder than were the condensates, the condensates would still perform better.
These and other aspects of the present invention will be shown in the following examples.

Example 1

Synthesis of bis-5,5'-(N-ethylbenzo[a]carbazolyl)phenylmethane.

Into a round bottom flask equipped with a reflux condenser and a mechanical stirrer were added 22.4 grams (0.1 mole-) of _N-ethylbenzo[a]carbazole and 5.3 grams (0.05 mole) of benzaldehyde. Two hundred milliliters of ethanol acidified with 8 ml of concentrated hydrochloric acid were then added. The mixture was stirred at reflux under a nitrogen atmosphere for sixteen hours. The insoluble, pure white product was isolated by filtration, washed with 100 ml of ethanol, and dried in a vacuum oven. The yield was 95% of the theoretic calculation.

Examples 2-17

In a manner substantially identical to that of the previous example, electronically active electron donor compounds of the present invention were obtained by condensing N-ethylbenzo[a]carbazole with each of the following aldehydes in equimolar replacement for the benzaldehyde:

2. p-tolualdehyde
3. m-tolualdehyde
4. o-tolualdehyde
5. p-anisaldehyde
6. m-anisaldehyde
7. o-anisaldehyde
8. p-chlorobenzaldehyde
9. p-bromobenzaldehyde
10. o-bromobenzaldehyde
11. p-hydroxybenzaldehyde
12. a-naphthaldehyde
13. veratraldehyde
14. p-octyloxybenzaldehyde
15. iso-butyraldehyde
16. n-nonylaldehyde
17. terphthaldehyde

Examples 18-21

In a manner substantially identical to that of . Example 1, the following combinations of carbazoles and aldehydes were used to synthesize compounds of the present invention.

18. benzo [a] carbazole and benzaldehyde
19. N-ethylbenzo [b] carbazole and benzaldehyde
20. N-ethyldibenzo[a]carbazole and benzaldehyde
21. N-ethyl-8-methoxybenzo[a]carbazole and benzaldehyde

The addition of any of the compounds produced in Examples 1-21 to electrically inert polymeric binders formed positive charge transport layers. These layers could be formed on photoconductive layers and were capable of supporting injected photogenerated holes from the photoconductive layer and allowed the transport of these holes through the transport layer to selectively discharge the surface charge.

Examples 22-39

Bulk sensitized photoreceptors were prepared by coating a solution consisting of 0.5 percent by weight solids of dye, 40 percent by weight of the same charge transport compound prepared in Example 1, and 59.5 percent of an organic solvent soluble polyester resin from a dichloromethane, 1,2-dichloroethane (50/50) solution were coated at about 1x10^-4 m wet thickness onto an aluminum coated polyethyleneterephthalate film. The sample was air dried at 85°C for approximately 15 minutes. The photoreceptor charged to a maximum voltage (V_o) under positive corona charging and the exposure energy and wavelength of radiation necessary to reduce the charge to one half V_o (V_f) with little dark decay was recorded. The device was also found to display high charge acceptance, low dark decay, and negligible fatigue upon cycling.
The following dye compounds were used in these examples.
The results are shown in Table I. Where the dyes had multiple peaks of absorbance, multiple readings were taken and the values for exposure energy and wavelength respectively given.
The general effectiveness of the dyes of the present invention as sensitizers for electron donors is shown by these examples.
The results of these experiments show that the sensitizing abilities of imidazo [4,5-b] quinoxaline cyaning dyes for organic electron donors are improved by the substitution of the phenyl ring on the imidazo [4,5-b] quinoxaline nucleus with a phenylsulfonyl or benzoyl group. It must be noted, in order to appreciate the data, that this is independent of the additional effect of counterions (anions) on the sensitizing ability of these cyanine dyes. As previously noted, certain counterions (and especially perchlorate) are preferred. As shown in Examples 35 and 36, the same quaternary nitrogen containing cyanine dye displayed improved sensitizing ability for organic electron donor compounds when the para-toluenesulfonate counterion was replaced with a perchlorate anion. However, comparisons are meaningful between, for example, the compounds of Examples 25 and 35 where the nitro groups of the prior art are replaced with phenylsulfonyl groups according to the present invention and the counterion is the same in both cases. As can be seen from the data, the exposure energy necessary to reach one-half the initial voltage was lower for the phenylsulfonyl compound at all absorbance wavelengths. This shows the improvement in sensitivity alleged in the practice of the present invention. The comparison of compounds 25 to compounds 35 (with only hydrogens on the phenyl ring) and 24 (with chlorine substituents on the phenyl ring) show similar improvement at the absorption wavelengths evaluated. Example 25 shows improved properties at its wavelength of maximum absorbance (621) in comparison to the wavelength of maximum absorbance !6S0) for compound 29.

Example 40

A solution consisting of 0.6g of an organic solvent soluble copolyester derived from terephthalic acid, isophthalic acid, and ethylene glycol (Vitel PE-200), 0.4g of bis-5,5'-(N-ethylbenzo[a]carbazolyl)-phenylmethane and 0.005g of phenylsulfonylimidazo-[4,5-b]-quinoxaline dye (A) in a mixture of 4.5g of dichloromethane and 4.5g of 1,2-dichloroethane was prepared, filtered, and knife coated onto an aluminized polyester substrate. The wet thickness of the coating was 4 mil (1x10^-4m). The coating was allowed to air dry and then was oven dried for 15 min. at 80°C. The electrophotographic performance of this construction is shown in Table II.

Examples 41-48

A solution consisting of 0.6g polyester (Vitel PE-200), 0.4g of the charge transport material indicated in Table II, and 0.005g a phenylsulfonylimidazo-[4,5-b]-quinoxaline dye (A) in a mixture of 4.5g of dichloromethane and 4.5g of 1,2-dichloroethane was prepared, filtered, and knife coated onto an aluminized polyester substrate. The wet thickness of the coating was 4 mil (1x10^-4m). The coating was allowed to air dry and then oven dried for 15 min. at 80°C. The electrophotographic behavior of this construction is shown in Table II.
Dye (A) has the structure

Example 49

A solution consisting of 1.0g of polyvinylcarbazole and 0.005g of phenylsulfonylimidazo-[4_f5-b]-quinoxaline dye (A) in a mixture of 4.5g dichloromethane and 4.5g of 1,2-dichloroethane was knife coated onto an aluminized polyester substrate. The wet thickness of the coating was 4 mil (1x10^-4m). The coating was air dried and then oven dried for 15 min. at 80°C. The electrophotographic behavior of the construction is shown in Table II.

Example 50

Preparation of 1-ethyl-2-[(1-ethyl-3,3-dimethyl-5-phenyl-sulfonylindolenine-2-yl)-4-chloro-3,5-trimethylene-1,3,5-heptatrienylidene]-3,3-dimethyl-5-phenylsulfonylindoleinium iodide.
0.45 g of l-ethyl-2,3,3-trimethyl-5-phenyl- sulfonylindoleninium iodide and 0.085 g of 1-formyl-2-chloro-3-hydroxymethylene-l,2-cyclohexene were dissolved in a mixture of 5 ml of acetic acid and 8 ml of acetic anhydride. After the addition of 0.12 g anhydrous sodium acetate, the reaction mixture was heated to reflux for 5 minutes and cooled overnight.- The raw dye was purified by recrystallization from acetic acid. 0.32 g of pure dye were obtained. The dye exhibited a melting point of 226-227°C, maximum absorbence at 788 nm (in acetone) and [e] = 2.57 x 1₀ ⁵.
The p-toluene sulfonate counterpart of this dye was equivalently prepared using the p-toluene sulfonate indoleninium salt, 0.9 of the cyclohexene, and 80 g of acetic acid. A yield of 1.8 g of purified dye exhibited a melting point of 213-215°C, a maximum absorbence at 788 nm (in acetone), and [ε] = 2.93 x 10⁵.
The 1-methyl indolenine iodide counterpart of this last compound was identically prepared using 1-methyl indoleninium salts. It displayed a melting point of 182-183°C, maximum absorbence at 786 nm (in acetone), and [ε] = 1.94 x 1₀5.

Example 51

Preparation of 1-ethyl-2-[(1-ethyl-3,3-dimethyl-5-phenylsulfonylindolenine-2-yl)-4-chloro-3,5-dimethylene-1,3,5-heptatrienylidene]-3,3-dimethyl-5-phenylsulfonylindoleninium p-toluenesulfonate.
A solution of 4.99 g l-ethyl-3,3-dimethyl-5-phenylsulfonylindoleninium p-toluenesulfonate and 1.25 g of l-dimethylammonium-methylene-2-chloro-3-dimethylamino-methylene-1,2-cyclopentene-chloride in 80 ml of acetic anhydride was prepared and heated at 110°C for ninety minutes. After cooling, the reaction solution was poured into ethyl ether with stirring. The solid material was filtered on a Buchner funnel and dissolved in 200 ml boiling acetone. The solution was poured into 400 ml of boiling water. The dye separated upon cooling, yielding 1.8 g of dye displaying a melting point of 193-195, maximum absorbence at 811 nm (in acetone) and [e] = 2.93 x ₁₀₅.

Example 52

Preparation of 1-ethyl-2-[(1-ethyl-3,3-dimethyl-5-benzoylindolenine-2-yl)-4-chloro-3,5-trimethylene-l,3,5-hetatrienylidene]-3,3-dimethyl-5-benzoylindoleninium p-toluenesulfonate.
A solution of 2.4 g of l-ethyl-2,3,3-trimethyl-5-benzoylindoleninium p-toluenesulfonate and 0.45 g of 1-formyl-2-chloro-3-hydroxymethylene-1,2-cyclohexene in 60 ml of acetic anhydride was prepared and heated at 100°C for one hour. After cooling at room temperature, the reaction solution was poured into 200 ml of ethyl ether and the solid material obtained was filtered on a Buchner funnel and repeatedly washed with ethyl ether. 0.5 g of pure dye was obtained by recrystallization from acetone. The dye displayed a melting point of 208-210°C, a maximum absorbence at 797 nm (in acetone), and [e] = 2.81 x 10⁵.

Example 53

Preparation of l-ethyl-2-[(I-ethyl-3,3-dimethyl-5-benzoylindolenine-2-yl)-4-chloro-3,5-dimethylene-1,3,5-heptatrienylidene]-3,3-dimethyl-5-benzoylindolenine p-toluenesulfonate.
A solution of 4.3 g l-ethyl-2,3,3-trimethyl-5-benzoylindoleninium p-toluenesulfonate and 1.17 g l-dimethylammonium-methylene-2-chloro-3-dimethyl- aminomethylene-1,2-cyclopentene in 80 ml of acetic anhydride was prepared and heated at 110°C for ninety minutes. After cooling at room temperature, the reaction solution was poured into 400 ml of ethyl ether with stirring. The solid product was filtered and redissolved in 800 ml of boiling acetone. This solution was poured into 400 ml of hot water. After cooling, 0.25 g of green dye was collected on a Buchner funnel and washed with 200 ml of an acetone/ethyl ether (1:4) solution. The dye displayed a melting point of 223-234°C, a maximum absorbence at 822 nm, and [e] = 2.67 x 10⁵.
Different counterions and substituents on these dyes may be readily obtained by appropriate selection of the reagents.

Example 54

A solution consisting of 0.6 g Vitel PE-200 organic solvent soluble polyester, 0.4 g of Bis-5,5'-(N-ethylbenzo[a]carbozylyl)-phenylmethane, and 0.005 g 5-phenylsulfonyl-indolenine dye 1 in a mixture of 4.5 g dichloromethane, and 4.5 g of 1,2-dichloroethane was prepared, filtered, and knife coated onto an aluminized polyester substrate. The wet thickness of the coating was 4 mil (1 x-10-⁴ m). The coating was allowed to air dry and was then oven dried for 15 minutes at 80°C. The electrophotographic performance of this construction, determined by measuring the energy required to discharge the sample to half of its initial value (E V_o/2), is shown in the accompanying Table.

Examples 55-76

A solution consisting of 0.6 g Vitel PE-200, 0.4 g of transport material indicated, and 0.005 g of the 5-phenylsulfonyl-indolenine dye indicated in a mixture of 4.5 g of dichloromethane and 4.5 g of 1.2-dichloroethane was prepared, filtered, and knife coated onto an aluminized polyester substrate. The wet thickness of the coating was 4 mil (1 x 10-⁴ m). The coating was allowed to air dry and then oven dried for 15 minutes at 80°C. The electrophotographic performance of these constructions, determined by measuring the energy required to discharge the sample to half of their initial values (E V_o/2). is shown in the accompanying Table.

Example 77

A solution consisting of 1.0 g of polyvinylcarbazole and 0.005 g of 5-phenylsulfonyl-indolenine dye 5 in a mixture of 4.5 g of dichloromethane and 4.5 g of 1,2-dichloroethane was knife coated onto an aluminized polyester substrate. The wet thickness of the coating was 4 mil (1 x 10-⁴ m). The coating was air dried and then oven dried for 15 minutes at 80°C. The electrophotographic behavior of this construction, determined by measuring the energy required to discharge the sample to half of its initial voltage (E V_o/2) is shown in the accompanying Table.

Examples 78-83

The procedures of Examples 21-42 were employed except that 0.005 g of 5-benzoyl-indolenine dyes were employed in place of the 5-phenylsulfonyl-indolenine dyes used previously. The electrophotographic behavior of these constructions, determined by measuring the energy required to discharge the samples to half of their initial voltage, are shown in the accompanying Table.

λmax = 813 nm
λmax = 809 nm ε = 3.32 x ₁₀ ⁵
λmax = 811 nm
λmax = 786 nm (acetone) e = 4.1 _{x 10} ⁵
λmax = 787 nm
λmax = 788 nm
5 ε = 2.57 x ₁₀ ⁵
λmax = 787 nm
λmax = 788 nm
λmax = 784 nm
λmax = 786 nm
λmax = 792 nm (acetone)
- e = 3.2 x 10⁵
- mp = 230-230.5°C
λmax = 794 nm
ε = 2.82 x ₁₀ ⁵
λmax = 792 nm
ε = 2.42 x 10⁵
λmax = 790 nm
λmax = 784 nm
λmax = 822 nm
ε = 2.21 x 10⁵
λmax = 822 nm (acetone)
- ε = 2.5 x ₁₀ ⁵
- mp = 246-247°C
λmax = 822 nm (acetone)
- e = 2.67 x 10⁵
- mp = 222-223.5°C
λmax = 797 nm
λmax = 797 nm
λmax = 797 nm

Example 84

A bulk sensitized photoreceptor was prepared by coating a solution of 10 percent by weight solids (5.2% of p-dimethylamino-di- -perfluoromethylsulfonylcinnamilidene, 38% bis(N-ethyl-l,2-benzocarbazolyl)phenyl methane, and 56.8% polycarbonate resin at about 1x10^-4m onto aluminized polyester(polyethyleneterephthalate). This was air dried for 15 minutes at 85°C. The sample was evaluated for its xerographic response to positive corona charging. The sample displayed a maximum sensitivity at 540 nm. At that wavelength, the construction required approximately 3 Joules/cm² to discharge the sheet to one half its potential from 740 volts. The sample displayed an initial discharge rate of 736 volts/sec. with 3.27 watts/cm².
The dye used in this example has the structure
The dyes having the structures
and
were also found to work well in the construction of this example.

Example 85

A coating solution was prepared from 0.6 g polyester (Vitel® PE-200 organic solvent soluble copolyester of terephthalic acid, isophthalic acid, and ethylene glycol), 0.4 g of the compound of Example 1, and 0.005 g of disulfone dye A in a mixture of 4.5 g dichloromethane and 4.5 g of 1,2-dichloroethane, filtered, then knife coated onto an aluminized polyester substrate. The wet thickness of the coating was 1 x 10-⁴m before oven drying for 15 minutes at 80°C. The electrophotographic performance of this coating is shown in Table I.

Examples 86-94

Coating solutions were prepared of 0.6 g of an organic solvent soluble copolyester derived from terephthalic acid, isophthalic acid and ethylene glycol (Vitel®PE-200), 0.4 g of the indicated charge transport material, and 0.005 g of the disulfone dye indicated in Table I. These materials were knife coated onto aluminized polyester from a solution with 4.5 g dichloromethane and 4.5 g of 1,2-dichloroethane after filtering. The wet thickness was 1 x 10-⁴m before air drying then oven drying for 15 minutes at 80°C. The electrophotographic performance of these coatings is shown in Table I.

Example 95

A coating solution of 1.0 g polyvinylcarbazole and 0.005 g disulfone dye D in a mixture of 4.5 g of dichloromethane and 4.5 g of 1,2-dichloroethane was knife coated at 1 x 10-⁴m wet thickness onto aluminized polyester. The coating was air dried then oven dried for 15 minutes at 80°C. The electrophotographic behavior of the construction is shown in Table I.

Disulfone Dyes

Claims

1. A photosensitive layer comprising an organic electronically active electron donor compound sensitized with a sensitizing amount of a dye selected from the group consisting of 1) an imidazo-[4,5-b]quinoxaline cyanine dye having at least one phenylsulfonyl or oenzoyl substituent on an imidazo-[4,5-b]^quinoxaline nucleus, 2) an indolenine cyanine dye bearing a phenylsulfonyl or benzoyl substituent on the 5-position thereof, and 3) a dye of the formula

wherein R_a represents a monovalent chromophoric radical, M represents sulfonyl

carbonyl

or carbonyloxy

R_f represents a highly fluorinated aliphatic radical, and R represents a monovalent electron-withdrawing radical.

2. The layer of claim 1 wherein said donor compound is a polyvinyl carbazole.

3. The layer of claim 1 wherein said donor compound is present in an electronically inactive polymeric binder.

4. The layer of claim 1 wherein said donor compound is a benzocarbazole derivative of the formula

where X is

wherein R⁴ and Y are independently selected from the group consisting of aliphatic, aromatic, heterocyclic, and mixed aliphatic-aromatic groups.

5. The layer of claims 2, 3, or 4 in which said dye is an imidazo-[4,5-b]quinoxaline cyanine dye isrepre- sented by any of the formula:

wherein W represents:

in which

g represents 1, 2 or 3;

R and R₁, which may be the same or different, each represents an aliphatic substituent or a phenyl group;

R₂ represents a phenylsulfonyl or a phenylcarbonyl group substituted in 6 or 7 position;

Z represents the atoms necessary to complete a nucleus from the group consisting of thiazole, benzothiazole, naphthothiazole, oxazole, benzoxazole, naphthoxazole, selenazole, benzoselenazole, thiazoline, pyridine, indolenine, 2-quinoline, 4-quinoline, 1-isoquinoline, 1,1-dialkyl-indolenine, imidazole, benzimidazole, naphthimidazole, imidazo-[4,5-b]-quinoxaline, 3H-pyrrolo-[2,3-b]-pyridine, 3H-nitro-indole, and thiazole-[4,5-b]-quinoline;

R₃ represents an aliphatic group or a phenyl group;

L represents a cation nucleus selected from the group consisting of indole, carbazole, isoxazole and pyrazole groups and

wherein X- represents an acid anion.

6. The emulsion of claim 5 wherein W represents

and g is 1 or 2.

7. The layer of claim 5 wherein W represents

8. The layer of claim 6 wherein g is 1, z is selected from the group consisting of thiazole, benzothiazole, oxazole and benzoxazole.

9. The layer of claim 7 wherein g is 1, and both R and R₁ are the same aliphatic substituent.

10. The emulsion of claim 7 wherein g is 1 and both R and R₁ are the same phenyl group.

11. The layer of claims 2, 3, or 4 in which said dye is an indolenine dye is represented by any of the formulae:

and

wherein:

and

B is selected from

and

n is a positive integer of 1 to 4,

m and q each represents a positive integer of 1 to 2,

p represents a positive integer of 1 to 3,

r is 0 or 1,

R² represents an acyclic hydrocarbon,

R¹ is a 6- or 7-position phenylsulfonyl or benzoyl substituent,

_R ⁵ and _R ⁶ are an aliphatic group,

_R ³ and R⁴ represent the same or different alkyl groups of 1-6 carbon atoms,

R⁷ is selected from the group consisting of H, halogen, cyano, alkyl, alkoxy, phenoxy, aryl, amino, thiophenyl, and thioalkyl,

Z represents the non-metallic atoms required to complete a heterocyclic nucleus of 5 to 6 ring atoms,

Q represents the non-metallic atoms required to complete a heterocyclic nucleus of 5 to 6 ring atoms, and

X represents an acid anion.

12. The layer of claims 2, 3, or 4 in which said indolenine dye is represented by the formula:

wherein,

n is 1,

r is 1,

_R ² is an aliphatic group of 1 to 13 carbon atoms,

_R ¹ is phenylsulfonyl or benzoyl,

_R ³ and R⁴ are selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl and hexyl,

_R ⁷ is halogen, and

X^- is an acid anion.

13. The layer of claims 2, 3, or 4 in which said indolenine dye is represented by the formula:

wherein

A is selected from

and

r is 1,

n is 1,

_R ² is an aliphatic group of 1 to 13 carbon atoms,

R¹ is a phenylsulfonyl or benzoyl group,

_R ³ and R⁴ are selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, and hexyl,

_R ⁵and _R ⁶ are alkyl of 1 to 6 carbon atoms,

_R ⁷ is halogen,

_X is an acid anion.

14. The layer of claims 2, 3 or 4 wherein M is sulfonyl.

15. The layer of claims 8, 9 or 10 wherein R is an alkyl group of 2 to 20 carbon atoms, phenyl group, naphthyl group or benzyl group, and M is sulfonyl.

16. An electrophotographic article comprising a substrate having in sequence on at least one surface thereof a conductive layer and the photosensitive layer of claims 1, 2, 4, 5, 6, 9, 10, 12, or 13.