Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Patent
1997-02-20
1998-08-25
Goodrow, John
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
430 72, 2522996, G03G 506
Patent
active
057981973
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the use of low molecular-weight or polymeric organic compounds which are present in the columnar-helical phase and have liquid-crystalline properties, as photoconductors or in electronic components, corresponding photoconductive layers, an electrophotographic recording material and a method for enhancing the photoconductivity.
Photoconductive polymers are an interesting class of materials and are used industrially on a large scale in copiers, laser printers and offset printing plates.
A number of attempts to improve the charge transfer characteristics of liquid-crystalline materials by orientation in the liquid-crystalline state are known. There are three approaches to this objective.
Firstly, low molecular-weight liquid-crystallines which form nematic phases at room temperature are doped with carbazole, the absorption capacity of the liquid-crystalline matrix being very limited, however. Even at very low concentrations (a few wt. %) the carbazole begins to crystallize. Accordingly, only a small photocurrent of the carbazole-doped liquid-crystalline samples is produced (compare L. L. Chapoy, D. K. Munck, K. H. Rasmussen, E. Juul-Diekmann, R. K. Sethi, D. Biddle, in Molecular Crystals, liquid-crystallines, Vol. 105, p. 353 et seq. (1984)).
The second approach is illustrated in EP-A-0 254 060. EP-A-0 254 060 discloses photoconductive films having a thickness of less than 20 .mu.m, which are produced from concentrated lyophase solutions of a polymer which has a repeating unit according to the general formula I, ##STR1## R being an alkylene radical having from 1 to 20 carbon atoms and P being a photoconductive group.
The third approach is described in EP-A-0 527 376. This describes low molecular-weight and polymeric organic photoconductors having generally diskotic liquid-crystalline properties with enhanced photoconductivity. A typical representative is hexaalkyloxytriphenylene, which has carrier charge mobilities of almost 10.sup.-3 cm.sup.2 /Vs (compare D. Adam, F. Closs, T. Frey, D. Funhoff, D. Haarer, H. Ringsdorf, R. Schuhmacher, K. Siemensmeyer, Phys. Rev. Lett., 1993, 70, 457).
It is an object of the present invention to provide organic compounds having liquid-crystalline properties, which in the liquid-crystalline state have an even higher photoconductivity or charge carrier mobility and which are suitable for use as photoconductors or in electronic components.
We have found that this object is achieved by the use of low molecular-weight or polymeric organic compounds which are present in the columnar-helical phase and have liquid-crystalline properties, as photoconductors or in electronic components.
Another object of the invention is a photoconductive layer which comprises a low molecular-weight or polymeric organic compound which is present in the columnar-helical phase and has liquid-crystalline properties.
A further object of the invention is an electrophotographic recording material which comprises an electroconductive base and a photoconductive layer of the abovementioned type.
The organic compounds used according to the invention, which have liquid-crystalline properties, generally have a photoconductivity of greater than 10.sup.-2 cm.sup.2 /Vs.
Low molecular-weight organic compounds having a columnar-helical phase which are suitable according to the invention include, for example, hexahexylthiotriphenylene and its mixtures with other hexaalkylthio-substituted derivatives, but also otherwise substituted triphenylenes, phthalocyanines, hexasubstituted benzenes, truxenes and hexa- or octasubstituted dibenzopyrenes, which have a columnar-helical phase.
Among these organic compounds triphenylene derivatives are preferred, particular preference in turn being given to triphenylene derivatives which contain thioalkyl substituents. A particularly suitable low molecular-weight organic compound which has a high charge carrier mobility and photoconductivity in a columnar-helical phase is 2,3,6,7,10,11-hexahexylthiotriphenylene.
The synthesis of 2,3,6,7,10,11-hexahexylthiotripheny
REFERENCES:
patent: 4865762 (1989-09-01), Kreuder et al.
patent: 5370820 (1994-12-01), Boden et al.
patent: 5393626 (1995-02-01), Closs et al.
"Fourier Transform Infrared Absorption Study of Hexa (Hexylthio) Tryphenylene : A Discotic Liquid Crystal", vol. 115, No. 6, (Aug. 1991), W. K. Lee, et al., p. 839.
"Conductivity and Structure of a Liquid-Crystalline Organic Conductor", vol. 117, No. 14, (Oct. 1992), G. B. M. Vaughan, et al., p. 700.
"Erste Fluessigkristalline Hexakis (Alkylthio) Triphenylene", vol. 108, No. 3 (Mar. 1984), p. 113 B. Kohne, et al.
"Towards a Photoconductive Liquid Crystal: Carbazole Containing Systems", L. L. Chapoy, et al., Mol. Cryst. Liq. Cryst. 1984, vol.15, pp. 353-374.
"Transient Photoconductivity in a Discotic Liquid Crystal", Physical Review Letters, vol. 70, No. 4, (Jan. 1993), D. Adam, et al.
"Fourier Transform Infrared Absorption Study of Hexa(Hexylthio)Triphenylene: A Discotic Liquid Crystal", W. K. Lee, et al., Mol. Cryst. Liq. Cryst., vol. 198, pp. 273-284 (1991).
Adam Dieter
Etzbach Karl-Heinz
Haarer Dietrich
Haussling Lukas
Kumar Sundeep
BASF - Aktiengesellschaft
Goodrow John
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