GB2070605A

GB2070605A - Thiopyrylium compounds, their preparation and use in photoconductive systems

Info

Publication number: GB2070605A
Application number: GB8106163A
Authority: GB
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1980-02-28
Filing date: 1981-02-26
Publication date: 1981-09-09
Also published as: GB2070605B

Abstract

A method of preparing a compound of the general formula: <IMAGE> in which: R<1> and R<2> independently represent a hydrogen atom, an optionally substituted alkyl aryl, aralkyl, cycloaliphatic or heterocyclic group providing R<1> and R<2> do not both represent cyclic groups of aromatic nature, or R<1> and R<2> together may represent the necessary atoms to complete a non-aromatic heterocyclic ring. R<3>, R<4>, R<5> and R<6> independently represent a hydrogen atom or any substituent providing the sum of their ???p constants has a value of less than +0.5, or R<3> and R<4> and/or R<5> and R<6> may represent the necessary atoms to complete an alicyclic or aromatic ring, R<3> and R<2> and/or R<1> and R<6> may represent the necessary atoms to complete a non-aromatic heterocyclic ring, R<7> and R<9> independently represent a hydrogen atom or any carbon linked substituent containing up to 16 carbon atoms. R<8> and R<10> independently represent a hydrogen atom, a C1-4 alkyl group or any two adjacent substituents R<7>, R<8>, R<9> and R<10> together may complete an alicyclic or aromatic ring, and X<6> represents an anion, comprising reacting in amine of the general formula: <IMAGE> in which R<1> to R<6> are as defined above, with a thiopyrylium salt of the general formula: <IMAGE> in which X<6> and R<7> to R<10> are as defined above, to yield the desired compound. The compounds of formula (I), many of which are new, are useful as sensitizers or photoconductors.

Description

SPECIFICATION Thiopyrylium compounds, their preparation and use in photoconductive systems This invention relates to thiopyrylium compounds, to their preparation and to their use as photoconductors or sensitizers in photosensitive elements for image recording. In particular the invention relates to 2-(4-aminophenyl)thiopyrylium compounds.

Photoconductive elements have achieved a broadly based acceptance in commercial technology.

Almost all of these systems utilize the phenomenon exhibited by certain materials to change their conductivity when struck by radiation to which they are sensitive and thus are able to selectively discharge accumulated electrical charges. One important area of research in this technical area has been an effort to sensitize these photoconductive materials to different and more useful portions of the electromagnetic spectrum and to increase the efficiency of the photoconductive effect.

Electrophotographic imaging systems are well known in the art, as shown, for example, in United States Patent Specification Nos. 2 221 776,2 277 013,2 825 814, 3 220 831, 3 61 5 414 and others.

One generally accepted type of unitary photoconductive construction comprises a substrate having a conductive layer on at least one surface and a photoconductive composition over said conductive layer. The inclusion of photosensitizing materials or adjuvants to the photoconductive material is conveniently used to change the sensitivity and/or speed of the construction, as shown in United States Patent Specification Nos. 2 987 395 and 3 250 615.

United States Patent No.3 615414 discloses the use of particulate discontinuous phases of pyrylium dyes in electrically insulating polymeric materials containing photoconductors to sensitize the photoconductive layer. Difficult and complex processing to effect the dispersion and agglomeration of the particle phases is disclosed therein to achieve some expansion of the range of spectral response for the photoconductors.

According to the present invention there is provided a method of preparing a compound of the general formula:

in which: R1 and R2 independently represent a hydrogen atom, an alkyl or substituted alkyl group, an aryl or substituted aryl group, an aralkyl or substituted aralkyl group, a cycloaliphatic or substituted cycloaliphatic group or a heterocyclic or substituted heterocyclic group providing R1 and R2 do not both represent cyclic groups or aromatic nature, or R' and R2 together may represent the necessary atoms to complete a non-aromatic heterocyclic ring, e.g. morpholine ring, R3, R4, R5 and R6 independently represent a hydrogen atom or any substituent providing the sum of their ap constants hasa value of less than +0.5, preferably +0.4, or R3 and R4 and/or R5 and R6 may represent the necessary atoms to complete an alicyclic or aromatic ring, R3 and R2 and/or R' and R6 may represent the necessary atoms to complete a non-aromatic heterocyclic ring, R7 and R9 independently represent a hydrogen atom or any carbon linked substituent containing up to 1 6 carbon atoms, preferably H, lower alkyl, phenyl or substituted phenyl.

R8 and R10 independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or any two adjacent substituents R7, R8, R9 and R10 together may complete an alicyclic or aromatic ring, and XO represents an anion, comprising reacting an amine of the general formula:

in which R1 to R6 are as defined above, with a thiopyrylium salt of the general formula:

in which XO and R7 to R10 are as defined above, to yield the desired compound.

The invention also extends to the preparation of compounds of general formula (I) in their basic form by treatment of the salt with a base, e.g. sodium hydroxide.

Many of the compounds prepared by the method according to the invention are new and therefore the invention also provides compounds of general formula (I) disclosed above including those in their basic form in which P1 to R'O and XO are as defined above with the proviso that when R'=R2=CH3 and R7=R9=C6H5 at least one of R3 to R6, R8 and R'O is other than a hydrogen atom.

The method of the invention may be conducted in a suitable solvent, e.g. alcohols such as ethanol, in many cases under gentle warming, or at reflux temperature. The products are generally slightly soluble in the cold reaction mixture.

The method of the invention is capable of preparing a wide range of compounds characterised by general formula (I). The amines of general formula (II) used as a starting material are readily available.

Many of the thiopyrylium salts of general formula (III) may be prepared according to the method disclosed by D. McKinnon in Canad. J. Chem. 48,338 (1970) in which 2H-thiopyran-2-ones and 4Hthiopyran-4-ones are reduced with lithium aluminium hydride to give the corresponding thiopyranols and these pseudo-bases were converted to the thiopyrylium perchlorates using perchloric acid. Thus the hydride reduction of thiopyranones provides a convenient route to thiopyrylium salts via the thiopyranol pseudo-bases.

A number of other routes for the preparation of thiopyrylium salts within general formula (Ill) are disclosed in the literature. For example, polycyclic thiopyrylium salts may be prepared according to the methods disclosed by B.D. Tilak, R.B. Mitra and Z. Muljiani, Tetrahedron 25, 1939 (1969) and S.D.

Tindal and B.D. Tilak, Indian J. Chem. 7, 637 (1969).

In general compounds of general formulae (Il) and (III) may have a wide range of substituents providing that in compound (II) there is a sufficiently high electron density in the para-position to the nitrogen and in compound (III) there is a sufficiently low electron density in the 2-position for the reaction to proceed.

The compounds of the invention are particularly useful as sensitizers or photoconductors and may be used, for example, in the systems disclosed in United States Patent Specification Nos. 3 250 615 and 3 61 5 414. The photosensitive elements comprise a support having coated thereon a layer of electrically insulating film-forming resin. The resin may be photoconductive or may act as a binder for a photoconductive compound. The support is usually conductive or has an integral conductive layer thereon. The compounds of the invention may be used as the photoconductor in such elements but preferably are used as a sensitizer to enhance the photoconduction of the layer.

Typical classes of photoconductive materials useful in electrophotography include 1) inorganic crystalline photoconductors, such as cadmium sulphide, cadmium sulphoselenide, cadmium selenide, zinc sulphide, 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, United States Patent Specification 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.United States Patent Specification No. 3 824 099 shows the use of squaric acid methine and triaryl pyrazoline compounds as an electrophotographic charge transport layer.

Cadmium sulphoselenide plates are shown in United States Patent Specification 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 United States Patent Specification No.3037861. 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 ai, Bull. Chem. Soc. Japan, Vol. 39, (1966) pages 1670 to 1673) but the carbazoles have continued to attract the greatest attention.

The use of carbazole condensates with aldehydes as shown in United States Patent Specification No. 4 025 341 are another useful class or organic photoconductors. Triaryl methanes including a carbazole moiety (as shown in Xerox Disclosure Journal, Vol. 3, No. 1 , Jan/Feb 1978, page 7) are also useful photoconductive insulators as are the materials of Japanese Patent Publication 52-34735.

Various binder materials known in the art are useful with electronically active donor compounds useful in the present invention. It is of course preferred that the binder be essentially opticallv transparent or at least electronically active 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, polya mides, 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, polyacrylates, polyesters and styrene/acrylonitrile copolymers.

Coating aids, lubricants, surface active agents, other sensitizing dyes and other adjuvants may be added to the composition.

For use of the materials of the present invention in electrophotographic layers, organic electron donor compounds should be present as at least 1 5 or 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 from 0.01 percent by weight up to 10 or 15% by weight dye may be used. 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 increase the sensitivity of the electron donor compounds. More preferred concentration ranges are between 0.05 and 10 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.

The photosensitive elements are utilized by imposing a uniform electrostatic charge on the surface of the insulating layer, exposing the charged surfaceimage-wise to light to dissipate the charge only in the light-struck areas thereby forming an electrostatic image on the surface and thereafter developing a visible image by means of the electrostatic image.

With regard to the compounds of general formulae (I) to (III) R1 and R2 may represent a wide variety of substituents as stated above providing R1 and R2 are not both cyclic groups of aromatic character. We have found that when R' and R2 are both cyclic groups, e.g. phenyl, the para-position of the phenyl ring. is deactivated and reaction with the thiopyrylium salt will not occur. Preferred substituents for R' and R2 include H, CH3, C2Hs, cyclo-C6H1t, CH2CH2OH, C6H5 and C6H5CH2.

R' and R2 together with the nitrogen atom to which they are attached may form a non-aromatic heterocyclic ring, e.g. a morpholine ring:

Also R1 and R6, and similarly R2 and R3, may represent the necessary atoms required to form a nonaromatic heterocyclic nucleus, for example:

R3 to R6 may represent a hydrogen atom or any substituent provided that the sum of the ap constants of R3 to R6 has a value less than +0.5. We have found that if the I:rsp exceeds +0.5 it is unlikely that the reaction will occur between the amine and thiopyrylium salt. Typical (Yp values for substituents may be found in the literature e.g. "A Critical Compilation of Substituent Constants", O.

Exner, Correiation Analysis in Chemistry, Edit. Chapman and Shorter, Plenum- Press 1 968. Examples of crp values are given in the following Table.

Me -0.14 NMe2 40:63 Et 4;13 NEt2 4.53 Prn 4.15 NHPh -0.27 Pri -0.13 NPh2 -0;29 Bun -0.19 NHAc 4.09 cyclo.C6H21 -0.13 NO2 +0.81 Ph 0.05 - OH -0.38 CH2Ph -0.06 OMe -0.28 CH2OR +0;02 OEt 4.14 CF3 +0.53 OPh +0.14 CHO +0;;47 SMe -0;07 COMe +0;47 SO2Me +0.73 COOH +0;44 F +0.15 COOR +0;44 Cl +0.24 NH2 4.30 Br +0.26 NHMe 40:46 1 +021

R7 and R9 may represent a hydrogen atom or any carbon-linked substituent containing up to 16 carbon atoms. Preferably R7 and P9 are hydrogen, aryl or substituted aryl.

Any of the adjacent substituents R3 to R10 may represent the necessary atoms to form a fused-on carboxylic or heterocyclic ring.

XO may be an anion, examples of which include C104, CF3SO3# and BF4.

A number of characteristics of these compounds, particularly when used as sensitizers for photoconductors in both solvent and bulk (aggregated) systems, distinguish them from the materials of the prior art. In comparing compounds of the prior art, such as, for example, 4-(4- dimethylaminophenyl)-2,6-diphenylthiopyrylium perchlorate (Compound 2 of U.S. Patent No.

3 61 5 414) with their structurally closest counterparts of the present invention, such as 2-(4dimethylaminophenyl)-4,6-diphenylthiopyrylium perchlorate, it has been noted that the compounds of the present invention tend to absorb radiation in longer wavelengths (e.g. greater than 700 nm and particularly greater than 7500 nm) in the aggregate form and also absorb radiation in solution at longer wavelengths. This is an extremely important capability. It is also quite surprising that a modest structural shift of the position of substituents will cause this change. The dramatic nature of this change can be seen in assuming a relative speed of 100 for each aggregated dye at 700 nm.The prior art dye indicated above exhibits a relative speed of less than 10 in a given organic photoconductor at 750 nm while the dye of the present invention exhibits a relative speed of over 70 in the same photoconductor.

Absolute speeds are also comparable at maximum absorbance, with less than 0.3 log units (usually less than 0.2 log units) variation between the dyes.

The invention will now be illustrated by the following Examples.

EXAMPLE 1 a) Preparation of 4,6-diphenyl-α-dithiopyrone Acetophenone (0.2 mole, 24 g) and pyrrolidine (0.24 mole, 77 g) were added to molecular sieves (Linde 5A) in anhydrous ether solution. The reaction mixture was shaken (100 h) and then filtered.

Molecular sieves were washed with ether(3 x 20 ml) and the combined filtrate was evaporated at 20 ml. 1-Pyrrolidinyl-1-phenylethylene was distilled (90 C, 0.25 mm) as an orange yellow oil (17.3 g 50%), boiling point 74 to 76 C. 1-Pyrrolidinyl-1-phenylethylene (0.1 mole, 17.3 g) and carbon disulphide (40 ml) in anhydrous dioxane (40 ml) were heated (600 C, 3 h). The excess of carbon disulphide was removed by distillation and a mixture of methanol (30 ml) and water (10 ml) was added.

The product was extracted with chloroform and the solvent was evaporated. The residue on recrystallization from methanol-dioxane (1:1) gave 4,6-diphenyl-.E-dithiopyrone, (16.8 9,60%) as red needles, melting point 114 to 11 50C.

b) Preparation of 2,4-diphenylthiopyrylium perchlorate To the 4,6-diphenyl-ar-dithiopyrone (16.8 g, 0.06 mole) suspended in acetic acid (680 ml) was added 30% H202 solution (17 ml) and the mixture maintained at 300C. The mixture became dark red in colour then siowly lightened to yellow. After 2 hours, 70% perchloric acid (21 ml) was added to the solution. Dilution with ether gave yellow needles of 2,4-diphenylthiopyrylium perchlorate which were recrystallized from acetic acid containing perchloric acid (13.2 g, 63.2%, melting point 156 to 1 570C).

2,4-Diphenylthiopyrylium trifluoromethane sulphonate (51%, melting point 1 880C) and 2,4diphenylthiopyrylium tetrafluoroborate (66%, melting point 1 650C) were prepared by a similar procedure but using trifluoromethanesulphonic acid or tetrafluoroboric acid to acidify the reaction mixture in place of perchloric acid.

c) Preparation of 2-(4-aminophenyl)-4,6-diphenylthiopyrylium perchlorate 2,4-Diphenylthiopyrylium perchlorate (1 g, 2.87 mmole) and aniline (0.54 g, 5.74 mmole) were heated in 10 ml of ethanol at 40 to 450C. The reaction mixture was immediately coloured deep blue.

After stirring was continued for two hours, the reaction mixture was allowed to stand at room temperature to give blue needles of 2-(4-aminophenyl)-4,6-diphenylthiopyrylium perchlorate. This compound was recrystallized from a mixture of ethanol-chloroform. Yield: 52%, 0.66 g, melting point 160 to 1620C.

Found: C, 62.25; H, 4.20; N, 274. C23H 16NSClO4 Calculated: C,62.800; H,4.10; N, 3.18.

,3 max. 584 (log E, 4.21), 367 $(log #, 4.27); T (DMSOd6) 1.42 (2H d thiopyrylium protons) 1.8-3.26 (16H, aromatic and NH2 protons).

EXAMPLES 2 TO 29 The salts listed in the following Table 1 were prepared in a similar manner to that in Example 1 from 2,4-diphenylpyrylium salt and the appropriate amine.

Table 2 reports the analysis, y max and log E max of each compound.

TABLE 1

Example melting point No. R R R R4 R5 R6 X C 1 H H H H H H CIO4 160-162 2 H H H H H H CF3SO3 207 3 CH3 H H H H H CIO4 206-208 4 CH3 H H H H H CF3SO3 216 5 CH3 CH3 H H H H CF3SO3 216 6 CH3 CH3 H H H H BF4 250 7 C2H5 C2H5 H H H H CF3SO3 145 8 C2H5 C6H5CH2 H H H H CF3SO3 174 9 C2H5 C6H5CH2 H H H H CIO4 175 10 C2H5 C6H5CH2 H H H H BF4 204 11 C6H5CH2 C6H5CH2 H H H H OF3SO3 231 12 H H CH3 H H H OF3SO3 202 13 H H CH3 H H H CIO4 250 TABLE 1 (Continued)

Example melting point NO. R R R R4 R5 R6 X C 14 H H H CH3 H H CF3SO3 220 15 H H H CH3 H H CIO4 165-168 16 CH3 CH3 H CH3 H H CF3SO3 105 17 H H CH3 H H CH3 CF3SO3 245-250 18 H H C2H5 H H C2H5 CF3SO3 187 19 H cyclo C6H21 H H H H CF3SO3 133 20 H C6H5 H H H H CF3SO3 193 21 H H OCH3 H H H CF3SO3 167 22 H H OCH3 H H H CIO4 248 23 H H H OCH3 H H CF3SO3 235 24 H H H OCH3 H H CIO4 165 25 H H H OCH3 H OCH3 CF3SO3 131 TABLE 1 (Continued)

Example melting point NO. R R R R4 R5 R6 X C 26 CH2CH2OH CH2CH2OH H H H H CIO4 63 27 H H H Cl H H CF3SO3 107-109 28 H H H Cl H H CIO4 170-172 29 H H NH2 H H H CF3SO3 250 TABLE 2

Calculated Found #'max, log #max.

Example No. C H N S C H N S (CHCl3) 1 62.8 4.1 3.2 - 62.2 4.2 2.7 - 584 4.21 (EtOH) 2 58.8 3.6 2.8 13.1 59.4 3.3 3.1 13.1 592 4.34 3 63.5 4.4 3.1 - 63.0 4.6 3.3 - 596 4.38 (EtOH) 4 59.6 4.0 2.8 12.7 62.3 3.9 2.7 13.1 633 4.55 5 60.3 4.2 2.7 12.4 61.0 4.0 2.5 12.4 624 4.77 6 66.0 4.8 3.1 7.0 67.5 4.2 3.4 6.4 622 4.86 7 61.6 4.7 2.6 11.7 63.0 4.6 2.6 11.6 638 4.50 8 65.2 4.6 2.3 10.5 64.6 4.2 2.2 10.4 620 4.53 9 68.9 5.0 2.5 5.7 70.6 4.2 2.7 5.9 615 5.18 10 70.5 5.2 2.6 5.9 72.4 4.4 2.8 5.7 620 5.05 11 68.1 4.5 2.1 9.6 67.8 3.9 2.0 9.7 602 4.50 12 59.6 4.0 2.8 - 62.8 3.8 2.7 - 600 4.32 13 63.5 4.4 3.1 - 62.9 4.6 3.0 - 596 4.32 (EtOH) 14 59.6 4.0 2.8 12.7 59.5 3.3 3.1 12.5 564 4.30 TABLE 2 (Continued)

Calculated Found #'max, log #max.

Example No. C H N S C H N S (CHCl3) 15 63.5 4.4 3.1 - 63.6 4.7 3.2 - 556 4.16 (EtoH) 16 61.0 4.5 2.6 12.1 60.8 4.6 2.7 12.1 616 2.30 17 60.3 4.3 2.7 12.4 62.1 3.8 2.6 12.3 600 4.32 18 61.6 4.8 2.6 11.7 62.1 4.6 2.5 12.3 602 4.32 19 63.0 4.9 2.4 11.2 63.0 4.8 2.6 10.8 634 4.31 20 63.7 3.9 2.5 11.3 63.2 3.6 2.2 12.0 650 4.39 21 57.8 3.8 2.7 12.3 59.4 3.7 2.6 12.5 612 4.32 22 61.3 4.3 3.0 - 61.2 4.4 2.6 - 588 4.19 (EtOH) 23 - - 2.7 12.3 - - 2.2 12.3 586 4.27 24 61.3 4.3 3.0 - 61.2 4.4 2.6 - 566 4.16 (EtOH) 25 56.8 4.0 2.5 11.7 17.3 3.6 2.5 11.2 602 4.36 26 61.4 5.0 2.6 6.1 60.7 5.1 2.7 6.5 638 4.31 27 55.0 3.2 2.7 12.2 56.5 3.2 2.2 10.8 564 4.00 28 - - - - - - - - 588 4.06 (EtOH) 29 57.1 3.8 5.6 12.7 56.7 3.2 5.6 12.1 654 EXAMPLE 30 Preparation of2,4-diphen yl-6( of ,2,3,4-tetrahydroquinoline-6-yl) thiopyrylium trifluoromethane sulphonate 2,4-Diphenylthiopyrylium trifluoromethane sulphonate (2.0 g) and 1 ,2,3,4-tetrahydroquinoline (1.4 g) in ethanol (20 ml) were heated at 900 for 30 minutes. After cooling the solution was poured into ether (50 ml) and the precipitated dye was filtered, washed with ether and recrystallized from ethanol as black needles having a melting point of 2330C, A max (CHCI3) 656 nm.

Found: C, 60.4; H, 4.2; N. 2.6; S, 12.3. C27H22F3NSO3 Calculated: C,61.2; H,4.2; N,2.6; S, 12.1.

EXAMPLE 31 Preparation of 2,4-Diphenyl-6(julolidin-6-yl) thiopyrylium trifloromethane sulphonate The same procedure as Example 30 was adopted using 2,4-dlphenylthiopyrylium trifluoromethane sulphonate (2.0 g) andjulolidine (1.7 g) in ethanol (20 ml). The dye was recovered in the form of black needles having a melting point of 211 OC, A max (CHCí3) 675 nm.

Found: C, 62.5; H, 4.7; N, 2.5; S. 11.5. C30H26F3NSO3 Calculated: C, 63.3; H, 4.6; N, 2.5; S, 11.3.

EXAMPLES 32 TO 45 Examples ofPhotoconduction Enhancement 5 g of a polycarbonate resin (Lexan 121, General Electric Corporation) were dissolved in 50 ml of 1 ,2-dichloro-ethane. To this solution were added 5 g of the photoconductor, 1,5-diphenyl-3-styryl-2- pyrazoline, and the mixture stirred until the solution was complete. To 10 ml of this solution was added 0.01 g of a thiopyrylium dye from Table 1, and when the dye had dissolved, the mixture was coated onto a thin aluminium sheet and dried, to give a film of 10 thickness. The film was then charged by a corona discharge to a surface potential, V, and then exposed to the light from a tungsten filament lamp in the instrument known as a Stati-Tester (manufactured by M/K Systems Inc.).The time required (t1/2v) for the initial potential, V, of the film to drop to half its initial value is compared to that required for a coating containing photoconductor but no dye. The enhancement of photoconduction by the dyes of this invention is demonstrated in the following Table 3.

TABLE 3

Example Initial Voltage (VO) Time to Vo/2 No. Dye (positive) (sec) 32. None 615 43 33 2 610 0;8 34 4 555- 0;9 35. 5 700 0;;7 36 7 540 1.6 37 11 210 1.1 38 12 365 1.0 39 14 525 0.9 40 15 625 1.0' 41 16 600 1.0 42- 17 345- 1.0 43 18 350- 0.3 44 27 780 45- 29 585 11.2 EXAMPLES 46 TO 56 The preparations and procedures of Examples 32 to 45 were repeated except that the photoconductor used was 5-(p-diethylaminophenyl)-3-(p-diethylaminostyryl)-1-phenyl-2-pyrazoline.

The data are reported in the following Table 4.

TABLE 4

Example Initial Voltage Time to Vo/2 No. Dye (VO) (positive) (sec) 46 None 585 - 6.0 47 2 400 1.2 48 4' 445 1.3 49 5. 475 1.2 - 50 7 465 1.4 51 8 415 - 1.0 52 17 440 . 1.2 53 18 420 1.5 - 54 21 450 1.2 55 23 445 1.1 56 25- 505- 1.8

Claims

1. A method of preparing a compound of the general formula:

in which: R and R independently represent a hydrogen atom, and alkyl or substituted alkyl group, an aryl or substituted aryl group, an aralkyl or substituted aralakyl group, a cycloaliphatic or substituted cycloaliphatic group or a heterocyclic or substituted heterocyclic group providing R and R do not both represent cyclic groups of aromatic nature, or R and R together may represent the necessary atoms to complete a non-aromatic heterocyclic ring, R3, R4, R5 and R6 independently represent a hydrogen atom or any substituent providing the sum of their #n constants has a value of less than+0.5, or R and R4 and/or R5 and R6 may represent the necessary atoms to complete and alicyclic or aromatic ring, R and R and/or R and R6 may represent the necessary atoms to complete a non-aromatic heterocyclic ring, R7 and R9 independently represent a hydrogen atom or any carbon linked substituent containing up to 16 carbon atoms.

R8 and R10 independentiy represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or any two adjacent substituents R7, R8, R9 and R10 together may complete an alicyclic or aromatic ring, and X# represents an anion, comprising reacting an amine of the general formula:

in which X# and R7 to R10 are as defined above, to yield the desired compound.

2. A method as claimed in Claim 1, in which R , R4, R5 and R6 independently represent a hydrogen atom or any substituent such that the sum of their ob constants has a value less than +0.4.

3. A method as claimed in Claim 1 or Claim 2, in which R and R are independetly selected from H, CH3, C2H5, C6H5, C6H5CH2, cyclo-C6H11 and CH2CH2OH.

4. A method as claimed in any preceding claim in which R3, R4, R5 and R6 are independently selected from H, alkyl, alkoxy, halogen and NH2.

5. A method as claimed in any one of Claims 1 to 3, in which R and R and/or R and R6 comprise the necessary atoms to complete a non-aromatic heterocyclic ring.

6. A method as claimed in any preceding claim in which R7 and R9 independently represent hydrogen, lower alkyl, phenyl or substituted phenyl.

7. A method as claimed in any preceding claim, in which R8=R10=H and R7=R9=C6H5.

8. A method as claimed in any preceding claim, which is conducted in a solvent at elevated temperature.

9. A method as claimed in Claim 8, which is conducted under reflux.

10. A method as claimed in Claim 1, substantially as herein described with reference to any one of Examples 1 to 29.

11. A method as claimed in Claim 1, substantially as hereindescribed with reference to Example 30 or Example 31.

12. A compound of the general formula:

in which: R1 and R2 independently represent a hydrogen atom, an alkyl or substituted alkyl group, or an aryl or substituted aryl group, an aralkyl or substituted aralkyl group, a cycloaliphatic or substituted cycloaliphatic group or a heterocyclic or substituted heterocyclic group providing R' and R2 do not both represent cyclic groups of aromatic nature, or R' and R2 together may represent the necessary atoms to complete a non-aromatic heterocyclic ring;; R3, R4, Ras and R6 independently represent a hydrogen atom or any substituent providing the sum of their ap constants has a value of less than +0.5, or R3 and R4 and/or R5 and P6 may represent the necessary atoms to complete an alicyclic or aromatic ring, R3 and R2 and/or R' and R6 may represent the necessary atoms to complete a non-aromatic heterocyclic ring, R7 and R9 independently represent a hydrogen atom or any carbon linked substituent containing up to 16 carbon atoms.

R8 and R10 independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or any two adjacent substituents R7, R8, R9 and R10 together may complete an alicyclic or aromatic ring.

and X# represents an anion, with the proviso that when R'=R2=CH3 and R7=R9=C6Hs at least one of R3 to R6, R8 and R10 is other than a hydrogen atom.

13. A compound as claimed in Claim 12, in which R3, R4, R5 and R6 independently represent a hydrogen atom or any substituent such that the sum of their a, constants has a value less than +0.4.

14. A compound as claimed in Claim 12 or Claim 13, in which R' and R2 are independently selected from H, OH3, C2Hs, C6H5, C6H5CH2, cyclo-C6H11 and OH 2CH2OH.

15. A compound as claimed in any one of Claims 12 to 14 in which R3, R4, R5 and R6 are independently selected from H, alkyl, alkoxy, halogen and NH2.

1 6. A compound as claimed in any one of Claims 12 to 14, in which R3 and R2 and/or R' and R6 comprise the necessary atoms to complete a non-aromatic heterocyclic ring.

in which: R' and R2 independently represent a hydrogen atom, an alkyl or substituted alkyl group, an aryl or substituted aryl group, an aralkyl or substituted aralkyl group, a cycloaliphatic or substituted cycloaliphatic group or a heterocyclic or substituted heterocyclic group providing R' and R2 do not both represent cyclic groups of aromatic nature, or R' and R2 together may represent the necessary atoms to complete a non-aromatic heterocyclic ring, e.g. morpholine ring, R3,R4,R5 and R6 independently represent a hydrogen atom or any substituent providing the sum of their ap constants has a value of less than +0.5, preferably +0.4, or R3 and R4 and/or R5 and R6 may represent the necessary atoms to complete an alicyclic or aromatic ring, R3 and R2 and/or R1 and R6 may represent the necessary atoms to complete a non-aromatic heterocyclic ring, R7 and R9 independently represent a hydrogen arom or any carbon linked substituent containing up to 16 carbon atoms, R8 and R'O independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or any two adjacent substituents R7, R8, R9 and R'O together may complete an alicyclic or aromatic ring, and XO represents an anion.

17. A compound as claimed in any one of Claims 12 to 16 in which R7 and R9 independently represent hydrogen, lower alkyl, phenyl or substituted phenyl.

1 8. A compound as claimed in any one of Claims 12 to 1 7, in which P6=P10=H and R7=R9=C6H5.

19. A compound as claimed in Claim 12 substantially as herein described with reference to any one of Examples 1 to 29.

20. A compound as claimed in Claim 12, substantially as herein described with reference to Example 30 or Example 31.

21. A sensitized photoconductive layer comprising a binder, an electron donating compound and a sensitizing amount of a thiopyrylium compound of the general formula:

in which R' to R10 are as defined in Claim 1.

22. An element as claimed in Claim 21 in which the thiopyrylium compound is in the form of a particulate discontinuous phase.

23. An element as claimed in Claim 21 or Claim 22 in which the thiopyrylium compound is a compound as claimed in any one of Claims 12 to 20.

24. An element as claimed in Claim 21 substantially as herein described with reference to any one of Examples 32 to 56.

25. A method of making the photoconductor element of Claim 22 comprising combining the binder, electron donor compound and the thiopyrylium compound in a solvent and allowing the thiopyrylium compound to auto-aggregate.