Polymers photocatalysts

A fully aromatic poly(cyclodiborazane) was prepared by hydroboration polymerization between DCA and mesitylborane. Since DCA is a highly fluorescent compound and widely used as a photocatalyst, the obtained polymer is expected to act as a novel type of electron transport material or polymer photocatalyst. The polymerization was carried out as Scheme 5, by adding a slight excess amount of mesitylborane (in THF) to a THF suspension of DCA at room temperature, and stirring the reaction mixture for 12h. The Mn of the polymer was found to be 4400 from the GPC measurement (CHCI3, PSt standards). 

Photoresists Photochromism Photochemical hole burning Photoresponsive polymers Photocatalysts Photoenergy conversion... 

Burke, N. A. D., TempHn, M., and GuiUet, J. E., The mechanism or perylene photo-oxygenation in a water-soluble polymer photocatalyst, /. Photochem. Photobiol. A Chem., 100, 93, 1996. 

In this section, Ru(bpy)j+ and its polymer analogoues are mainly described, since the Ru complex is best known as the photocatalyst that can photolyze water theoretically. 

Bis(2,2 -bipyridyl)ruthenium(II) was anchored onto poly(4-vinyIpyridine) (PVP) (6) 28>29), but the polymer complex is not suitable as photocatalyst, because it is susceptible to photoaquation. A polymer complex containing Ru bpy) + pendant groups was first prepared by reaction of polystyrene (PSt) as shown in Eq. (15)30). 

We have shown how the band structure of photoexcited semiconductor particles makes them effective oxidation catalysts. Because of the heterogeneous nature of the photoactivation, selective chemistry can ensue from preferential adsorption, from directed reactivity between adsorbed reactive intermediates, and from the restriction of ECE processes to one electron routes. The extension of these experiments to catalyze chemical reductions and to address heterogeneous redox reactions of biologically important molecules should be straightforward. In fact, the use of surface-modified powders coated with chiral polymers has recently been reputed to cause asymmetric induction at prochiral redox centers. As more semiconductor powders become routinely available, the importance of these photocatalysts to organic chemistry is bound to increase. 

The first studies reported in the literature on PMRs were carried out in order to identify the best techniques for confining the photocatalyst, to choose suitable polymers for the membranes stable under UV-Vis illumination and to find the influence of some photocatalytic variables on the process [77-79]. 

We have already seen that photoactive clusters, e.g. CdS, can be introduced into vesicles and BLMs (Sect. 5.2 and 5.3). Similar support interactions are possible with both inorganic and organic polymeric supports. Photoactive colloidal semiconductor clusters can be introduced, for example, into cellulose [164], porous Vycor [165], zeolites [166], or ion exchange resins [167]. The polymer matrix can thus influence the efficiencies of photoinduced electron transfer by controlling access to the included photocatalyst or by limiting the size of the catalytic particle in parallel to the effects observed in polymerized vesicles. As in bilayer systems,... 

Dyes such as erythrosin B [172], eosin [173-177], rose bengal [178,179], rhodamines [180-185], cresyl violet [186-191], thionine [192], chlorophyll a and b [193-198], chlorophyllin [197,199], anthracene-9-carboxylate [200,201], perylene [202,203] 8-hydroxyquinoline [204], porphyrins [205], phthalocyanines [206,207], transition metal cyanides [208,209], Ru(bpy)32+ and its analogs [83,170,210-218], cyanines [169,219-226], squaraines [55,227-230], and phe-nylfluorone [231] which have high extinction coefficients in the visible, are often employed to extend the photoresponse of the semiconductor in photoelectro-chemical systems. Visible light sensitization of platinized Ti02 photocatalyst by surface-coated polymers derivatized with ruthenium tris(bipyridyl) complex has also been attempted [232,233]. Because the singlet excited state of these dyes is short lived it becomes essential to adsorb them on the semiconductor surface with... 

Nakahira, T. Inoue, Y. Iwasaki, K. Tanigawa, H. Kouda, Y. Iwabuchi, S. Kojima, K. Graetzel, M. Visible light sensitization of platinized Ti02 photocatalyst by surface-coated polymers derivatized with ruthenium tris(bipyridyl), Makromol. Chem., Rapid Commun. 1988, 9, 13. 

After light absorption by the photocatalyst the next step is photoproduction of free radicals that initiate polymerization of the acrylate unsaturated monomers, oligomers, and polymers contained in the UV-curable coating system. 

The photooxidation and photodegradation of polymers continues to attract some interest but is not as widespread as in previous years. Review articles have appeared dealing with poly(2,6-dimethyl-l,4-phenylene oxides) , photocatalyst fibres, polymers with azo links and accelerated weathering specifications. Other articles of interest include the design of an integrating sphere for repeatability in polymer ageing and the use of FTIR for monitoring the photostability of clearcoats . 

K.G. Kanade, Jin-OoK Baeg, U.P. Mulik, D.P. Amalnerkar, B.B. Kale, Nano-CdS by polymer-inorganic solid-state reaction Visible light pristine photocatalyst for hydrogen generation , Materials Research Bulletin, 41, 2219-2225, (2006). 

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