A photoconductive layer sensitized by a compound of the general formula: ##STR1## in which: R.sup.1 and R.sup.2 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.sup.1 and R.sup.2 do not both represent cyclic groups of aromatic nature, or R.sup.1 and R.sup.2 together may represent the necessary atoms to complete a non-aromatic heterocyclic ring, PA0 R.sup.3, R.sup.4, R.sup.5 and R.sup.6 independently represent a hydrogen atom or any substituent providing the sum of their .sigma..sub.p constants has a value of less than +0.5, or R.sup.3 and R.sup.4 and/or R.sup.5 and R.sup.6 may represent the necessary atoms to complete an alicyclic or aromatic ring, R.sup.3 and R.sup.2 and/or R.sup.1 and R.sup.6 may represent the necessary atoms to complete a non-aromatic heterocyclic ring, PA0 R.sup.7 and R.sup.9 independently represent a hydrogen atom or any carbon linked substituent containing up to 16 carbon atoms, PA0 R.sup.8 and R.sup.10 independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or any two adjacent substituents R.sup.7, R.sup.8, R.sup.9 and R.sup.10 together may complete an alicyclic or aromatic ring, and PA0 X.sub.- represents an anion.

FIELD OF THE INVENTION 
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. 
BACKGROUND OF THE INVENTION 
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 U.S. Pat. Nos. 2,221,776; 2,277,013; 2,825,814; 3,220,831; 
3,615,414, 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 U.S. Pat. Nos. 2,987,395 and 
3,250,615. 
U.S. Pat. No. 3,615,414 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 particule phases are disclosed therein to achieve 
some expansion of the range of spectral response for the photoconductors. 
SUMMARY OF THE INVENTION 
According to the present invention there is provided a method of preparing 
a compound of the general formula: 
##STR2## 
in which: 
R.sup.1 and R.sup.2 independently represent a hydrogen atom, an alkyl or 
substituted alkyl group (preferably of up to 20 carbon atoms, more 
preferably of 1 to 8 carbon atoms), an aryl or substituted aryl group 
(preferably of up to 20 carbon atoms, more preferably phenyl), an aralkyl 
or substituted aralkyl group (preferably of up to 20 carbon atoms, 
preferably up to 10 carbon atoms), a cycloaliphatic or substituted 
cycloaliphatic group (preferably of 3 to 6 ring atoms) or a heterocyclic 
or substituted heterocyclic group (preferably of C, S, N and O atoms in 5, 
6 or 7 membered rings) providing R.sup.1 and R.sup.2 do not both represent 
cyclic groups of aromatic nature, or R.sup.1 and R.sup.2 together may 
represent the necessary atoms to complete a non-aromatic heterocyclic ring 
comprised of C, S, N and O ring atoms, preferably of 5, 6 or 7 ring atoms, 
e.g. morpholine ring, 
R.sup.3, R.sup.4, R.sup.5 and R.sup.6 independently represent a hydrogen 
atom or any substituent providing the sum of their .sigma..sub.p constants 
(Hammet sigma, para) has a value of less than +0.5, preferably +0.4, or 
R.sup.3 and R.sup.4 and/or R.sup.5 and R.sup.6 may represent the necessary 
atoms to complete an alicyclic or aromatic ring (preferably of 5, 6 or 7 
ring atoms, preferably selected from C, S, N and O, preferably of up to 20 
carbon atoms on the group), R.sup.3 and R.sup.2 and/or R.sup.1 and R.sup.6 
may represent the necessary atoms to complete a non-aromatic heterocyclic 
ring (preferably comprised of C, S, N and O ring atoms, preferably with 5, 
6 or 7 ring atoms, preferably with up to 20 carbon atoms in the group), 
R.sup.7 and R.sup.9 independently represent a hydrogen atom or any carbon 
linked substituent containing up to 16 carbon atoms, preferably 
hydrocarbons such as alkyl and phenyl groups (preferably up to 4 carbons 
in the former and up to 10 carbons in the latter), 
R.sup.8 and R.sup.10 independently represent a hydrogen atom, an alkyl 
group having 1 to 4 carbon atoms, a phenyl group, or any two adjacent 
substituents R.sup.7, R.sup.8, R.sup.9 and R.sup.10 together may complete 
an alicyclic or aromatic ring (preferably hydrocarbon aromatic rings, most 
preferably benzene groups, substituted or not), and 
X.sup.- represents an anion, 
comprising reacting an amine of the general formula: 
##STR3## 
in which R.sup.1 to R.sup.6 are as defined above, with a thiopyrylium salt 
of the general formula: 
##STR4## 
in which X.sup.- and R.sup.7 to R.sup.10 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 R.sup.1 
to R.sup.10 and X.sup.- are as defined above with the proviso that when 
R.sup.1 =R.sup.2 =CH.sub.3 and R.sup.7 =R.sup.9 =C.sub.6 H.sub.5 at least 
one of R.sup.3 to R.sup.6, R.sup.8 and R.sup.10 is other than a hydrogen 
atom. Many of these compounds have been found to autoassociate within 
photoconductive insulator layers and therefore not require the 
extraordinary processing requirements disclosed in U.S. Pat. No. 
3,615,414. 
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 characterized by general formula (I). The amines of general 
formula (II) used as a starting material are readily available. 
DETAILS OF THE PRESENT INVENTION 
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-thipoyran-2-ones and 4H-thiopyran-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 thiapyrylium salts via the 
thiopyranol pseudo-bases. 
A number of other routes for the preparation of thiopyrylium salts within 
general formula (III) are disclosed in the literature which enable 
production of all of the compounds of the present invention. 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 (II) 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 systems such as those 
disclosed in U.S. Pat. Nos. 3,250,615 and 3,615,414. The photosensitive 
elements generally comprise a support having coated theren 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, 
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. 
Pat. 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. 
Pat. No. 3,824,099 shows the use of squaric acid methine and triaryl 
pyrazoline compounds as an electrophotographic charge transport layer. 
Cadmium sulfoselenide plates are shown in U.S. Pat. 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. Pat. 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) 
pages 1670-1673), but the carbazoles have continued to attract the 
greatest attention. 
The use of carbazole condensates with aldehydes as shown in U.S. Pat. No. 
4,025,341 are another useful class of organic photoconductors. Triaryl 
methanes including a carbazole moiety (as shown in Xerox Disclosure 
Journal, Vol. 3, No. 1, January/February 1978, page 7) are also useful 
photoconductive insulators as are the materials of Japanese Patent 
Publication No. 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 optically 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, 
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, 
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 15 
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 surface image-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) R.sup.1 and 
R.sup.2 may represent a wide variety of substituents as stated above 
providing R.sup.1 and R.sup.2 are not both cyclic groups of aromatic 
character. We have found that when R.sup.1 and R.sup.2 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.sup.1 and R.sup.2 include H, CH.sub.3, C.sub.2 H.sub.5, 
cyclo-C.sub.6 H.sub.11, CH.sub.2 CH.sub.2 OH, C.sub.6 H.sub.5 and C.sub.6 
H.sub.5 CH.sub.2. 
R.sup.1 and R.sup.2 together with the nitrogen atom to which they are 
attached may form a non-aromatic heterocyclic ring, e.g. a morpholine 
ring: 
##STR5## 
Also R.sup.1 and R.sup.6, and similarly R.sup.2 and R.sup.3, may represent 
the necessary atoms required to form a non-aromatic heterocyclic nucleus, 
for example: 
##STR6## 
R.sup.3 to R.sup.6 may represent a hydrogen atom or any substituent 
provided that the sum of the .sigma..sub.p constants of R.sup.3 to R.sup.6 
has a value less than +0.5. We have found that if the .sigma..sub.p 
exceeds +0.5 it is unlikely that the reaction will occur between the amine 
and thiopyrylium salt. Typical .sigma..sub.p values for substituents may 
be found in the literature, e.g. "A Critical Compilation of Substituent 
Constants", O. Exner, Correllation Analysis in Chemistry, Edit. Chapman 
and Shorter, Plenum Press 1968. Examples of .sigma..sub.p values are given 
in the following Table. 
______________________________________ 
Me -0.14 NMe.sub.2 
-0.63 
Et -0.13 NEt.sub.2 
-0.53 
Pr.sup.n -0.15 NHPh -0.27 
Pr.sup.i -0.13 NPh.sub.2 
-0.29 
Bu.sup.n -0.19 NHAc -0.09 
cyclo.C.sub.6 H.sub.11 
-0.13 NO.sub.2 
+0.81 
Ph 0.05 OH -0.38 
CH.sub.2 Ph -0.06 OMe -0.28 
CH.sub.2 OR +0.02 OEt -0.14 
CF.sub.3 +0.53 OPh +0.14 
CHO +0.47 SMe -0.07 
COMe +0.47 SO.sub.2 Me 
+0.73 
COOH +0.44 F +0.15 
COOR +0.44 Cl +0.24 
NH.sub.2 -0.30 Br +0.26 
NHMe -0.46 I +0.21 
______________________________________ 
R.sup.7 and R.sup.9 may represent a hydrogen atom or any carbon-linked 
substituent containing up to 16 carbon atoms. Preferably R.sup.7 and 
R.sup.9 are hydrogen, aryl or substituted aryl (preferably phenyl). 
Any of the adjacent substituents R.sup.3 to R.sup.10 may represent the 
necessary atoms to form a fused-on carbocyclic or heterocyclic ring, 
preferably of 5, 6 or 7 ring atoms, with the heterocyclic rings preferably 
comprised of C, S, N and O atoms. 
X.sup.- may be any anion, particularly acid anions, examples of which 
include ClO.sub.4.sup.-, CF.sub.3 SO.sub.3.sup.-, p-toluene sulfonate, and 
BF.sub.4.sup.-. 
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. Pat. No. 3,615,414) with their structurally closest counterparts 
of the present invention, such as 
2-(4-dimethylaminophenyl)-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 750 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.