Photoconductive phthalocyanine

Photoconductive phthalocyanine compounds are usually prepared by the photoreceptor makers and their subsidiaries, and are not commercially available. For titanyl phthalocyanine, only crude material, which requires appropriate treatment to fine tune the desirable photosensitivity, is available from Sanyo Color Works, Orient Chemicals, and Toyo Ink Manufacturing. Such products may also cost several thousand dollars a kilogram. 

Cao L, Chen HZ, Wang M, Sun JZ (2002). Photoconductivity study of modified carbon nanotube/ oxotitanium phthalocyanine composites. J. Phys. Chem. B 6 8971-8975. 

The low stability of the magnesium porphyrins has precluded most potential applications. Other metallotetrapyrroles have found industrial uses for oil desulfurization, as photoconducting agents in photocopiers, deodorants, germicides, optical computer disks, semiconductor devices, photovoltaic cells, optical and electrochemical sensing, and molecular electronic materials. A few scattered examples of the use of Mg porphyrins in nonlinear optical studies have appeared" and magnesium phthalocyanines have been used in a few studies as semiconductor or photovoltaic materials" " One of the few... 

In systems in which the charge-transfer excitation band differs from the action spectrum of photoconductivity, the doping effect may be due to a change of recombination path that results in an enhancement of carrier liefetime (e.g. holes in merocyanines and phthalocyanines). (Details on the mechanism are given in 10,11,74).)... 

Merocyanines, phthalocyanines, pyrazines based on aceanthraquinoxalines, and several arylidine-l,3-indandiones exhibit -type photoconductivity. 

The photoconductivity of organic dyes, especially phthalocyanine pigments, could be utilized to provide reusable or non-reusable electrophotographic plates having sensitivities that extend over the entire visible spectrum and produce high-contrast images 167,168) Microcrystalline dispersions of metal-free phthalocyanine in suitable binders have a white-light sensitivity equal to that of selenium 169> and can be incorporated into coated papers and drums. 

Photoelectrochemical behavior of metal phthalocyanine solid films (p-type photoconductors) have been studied at both metal (93,94,95,96) and semiconductor (97,98) electrodes. Copper phthalocyanine vacuum-deposited on a Sn02 OTE (97) displayed photocurrents with signs depending on the thickness of film as well as the electrode potential. Besides anodic photocurrents due to normal dye sensitization phenomenon on an n-type semiconductor, enhanced cathodic photocurrents were observed with thicker films due to a bulk effect (p-type photoconductivity) of the dye layer. Meier et al. (9j>) studied the cathodic photocurrent behavior of various metal phthalocyanines on platinum electrodes where the dye layer acted as a typical p-type organic semiconductor. 

Phthalocyanines were chosen for these experiments because they are electronic semiconductors and because they are quite stable materials — an important consideration in fabricating any practical gas-detecting device. A considerable body of literature exists describing the physical and chemical properties of the phthalocyanines. A review of the work prior to 1965 is contained in the chapter by A. B. P. Lever in Volume 7 of Advances in Inorganic Chemistry and Radiochemistry (2). Electrical properties of phthalocyanines have been receiving increased attention in recent years. The photoconductivity of metal-free phthalocyanine has been studied in detail (3,4). Electrical properties of lead phthalocyanine have been studied extensively, especially by Japanese workers (5, ,7,8i). They have also studied the alteration of the conductivity of this material upon exposure to oxygen ( ,10.). The effects of a series of adsorbed gases (0, , CO, and NO) on the conductivity of iron phthalo-... 

Law (1993) has reviewed the widespread polymorphism in phthalocyanines and its relationship to their photoconductivity and use in xerographic applications. These are best demonstrated by the prototypical copper phthalocyanine CuPc (6-XIX, M = Cu), whose structural chemistry is discussed in detail in Section 8.3.3.1. The polarized absorption spectra of five forms are given in Fig. 6.9. One outstanding feature of these spectra is the rather intense red shifted band at 770 nm in the 5 and modifications compared to the solution absorption at 678nm (Law 1993). This... 

Yagishita, T., Ikegami, K., Narusawa, T. and Okuyama, H. (1984). Photoconduction of copper phthalocyanine-binder photoconductor sensitized with poly-A-vinylcarbazole. IEEE Trans. Ind. Appl, IA-20, 1642-6. [207]... 

Phthalocyanines with photoconductive and electrochromic properties 87YGK837. 

Titanyl phthalocyanine (TiOPc) is probably the phthalocyanine most often utilized in eommercial eleetrophotographic photoreeeptors. In a study of the wavelength dependence of photoconductivity in single- and dual-layer photoreceptors it was concluded that the pigment was p-type and that generation occurred in the pigment bulk and was unaffected by the presence of a hole-transport molecule electron donor [34n]. The pigment form was not identified in this study. 

An electrode covered with several molecular layers of dye could be made to adsorb all of the visible light, and obviate the need for the multielectrode stack. Very thick dye layers have tended not to be conductive or highly photoconductive so that their photoelectrochemical efficiencies are no better and perhaps worse than those seen on electrodes modified with very thin dye films. Molecular disorder of the dye appears to be the dominant reason for lack of conductivity in thick films of fluorescein-type, cyanine-type, and phthalocyanine-type dyes (12). It has been shown however that ordered molecular systems (mainly conjugated, highly unsaturated hydrocarbons) have considerable potential as conductive media, and that these ordered systems may be used to chemically modify electrode surfaces (12, 15). 

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