Poly photogeneration

Photoconducting polymers such as poly (JV-vinylcarbazole) are used in xerography or electrophotography, since the photogenerated charge carriers can travel through the polymer film with relative facility before getting immobilized or trapped (Roberts,... 

Subsequently, a resist system was reported that is composed of polymers containing recurrent acid-labile pendant groups in combination with an ar-ylonium salt-acid photogenerator (64-67). An example of the type of polymer used in this work is poly(p-tert-butyloxycarbonyloxystyrene) (t-BOC-sty-rene). 

Scheme VI. Processing of poly(t-BOC-styrene)-onium salt resists. The steps are (1) photogeneration of an extremely strong protonic acid from a triaryl-sulfonium or diaryliodonium salt and (2) baking, which allows acid-catalyzed deblocking of the t-BOC groups. Thus, irradiated areas of the polymer are converted to a much more polar form.

Large third order susceptibilities have recently been observed for trans-polyacetylene, heteroaromatic polymers, and poly[p-phenylene vinylene] (4-11). Such nonlinear phenomena in electroactive polymers due to intense laser irradiation has been linked to the photogeneration of charged solitons on time scales of the order 10 s, and values of (3w-w+w+w)—4x 10 esu for... 

Linear and 2D branched poly(diarylcarbene) systems95 were much pursued as prototypical potential magnetic systems (Fig. 8). For example, Iwamura and coworkers developed synthetic methodologies to put many diazo sites (photochemical carbene precursor sites) into proper connectivity to photogenerate all or most of the carbene sites. Itoh and coworkers developed methods to obtain and analyze HS ESR spectra of polycarbenes and polycarbene ions.96 Although... 

In order to learn about the true quantum efficiency of photogeneration one therefore has to study the photoinduced charge generation mechanism at faster time scales. Pump probe spectroscopy utilising a few optical-cycle laser pulses (5-6 fs) in the visible spectral range with broadband frequency conversion techniques [89] now makes it possible to study extremely fast optically-initiated events with unprecedented time resolution. Such a setup was used to time-resolve the kinetics of the charge transfer process from a polymer chain to a fullerene moiety in thin films of poly[2-methoxy, 5-(3, 7 -dimethyl-octyloxy)]-p-phenylene vinylene (MDMO-PPV) and [6,6]-phenyl C6i butyric acid methyl ester (PCBM). Solutions prepared from 1 wt% solutions of toluene on thin quartz substrates were studied. 

The earliest all-organic photoconductive compositions consisted of poly-vinyl(carbazole) (PVK, 1) and 2,4,7-trinitrofluorenone (TNF, 2) [25], In spite of its historical importance, the PVK/TNF system is an unusual one, because it is one of the few photoconductors which acts simultaneously as a photogenerator of primary charges and the medium in which the charge transport is accomplished. It is much more usual to employ a separate charge generator and a distinct transport medium. 

Figure 20 The spectral dependencies of the photogeneration efficiencies of vapor-deposited amorphous (lower curve) and poly crystalline (upper curve) layers of PECI. The efficiencies were computed on an incident photon basis.

Hor and Popovic (1994) measured photogeneration efficiencies of dispersions of HOGaPc in poly (vinyl butyral) (PVB) by delayed-field collection and field-induced fluorescence quenching techniques. The HOGaPc polymorph was described as type V. The transport layers contained N,N -diphenyl-N,N -bis(3-methylphenyl)-(l,r-biphenyl)-4,4 -diamine. Like many phthalocyanines, HOGaPc exhibits a linear correlation of the photogeneration and field-induced... 

Due to its relevance o single-layer photoreceptors, photogeneration in polymers is of considerable importance to xerography. The most widely studied are the polysilanes, poly(N-vinylcarbazole), and various doped polymers. 

Kuvshinskij et al. (1991) measured photogeneration efficiencies of poly(N-epoxypropylcarbazole) sensitized with rhodamine 6G. Kuvshinskij et al. argued that the photogeneration occurs via two concurrent mechanisms. The principal mechanism is a thermalization process that creates a bound electron-hole pair where the hole resides on one of the carbazole pendent groups and the electron on an excited dye molecule. A secondary process involves exciplex dissociation. The dissociation energy of the exciplex was reported as 0.54 eV. 

DiMarco et al. (1986) investigated photogeneration of charge-transfer complexes formed between poly[bis-(2-naphthoxy)phosphazene] and 2,4,7-... 

It is neccessary that the binder polymers (1) be compatible with diazoniun salts, (2) be uniform in film thickness when the layer is coated on the photoresist film, (3) show a high gas permeability to allow nitrogen photogenerated during the exposure of diazonaphtoquinone resist to diffuse. Many water soluble polymers were examined, and it has been found that poly(N-vinyl pyrrolidone) and its copolymers satisfy the above requirements. 

Figure 8. Wavelength dependence of the photogeneration efficiency in poly(Ar-vinylcarbazole). (Reprinted with permission from Ref [28c].)...

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