Polymeric photosensitizers have been widely used in photochemical reactions. However, the efficiency of these polymeric photosensitizers was generally lower than the corresponding low molecular weight (LMW) photosensitizers used so far. We have recently proposed [1][2][3] the concept of a multifunctional polymeric photosensitizer having both pendant substrate-attracting groups and photosensitizing groups, and it was found that the polymers containing cationic substrate-attracting groups and photosensitizing groups had a higher photosensitization efficiency than the corresponding LMW photosensitizers.
Multifunctional polymeric photosensitizers containing both pendant nitroaryl groups as photosensitizing moieties and pendant carboxylates as a substrate-attracting group were synthesized by radical copolymerization of p-(4nitrophenoxy)methylstyrene (NPMS) or p-(4-nitro-l-naphthoxy)methylstyrene (NNMS) with methacrylic acid (MA) followed by neutralization of the resulting copolymers with various bases such as NaOH, KOH or LiOH.
Since the thus obtained polymers were soluble in methanol and water, the photo-isomerization of (2cinnamoyloxy)ethyltrimethylammonium bromide was essentially carded out in water and a mixed solvent of water/ methanol in the presence of the photosensitizers. These results suggested that multifunctional polymeric photosensitizers containing both pendant photosensitizing groups and anionic substrate-attracting groups prepared from NPMS-MA have higher photosensitization efficiency than the polymeric photosensitizer prepared from NNMS-MA. Furthermore, it was found that the photosensitization efficiency was strongly affected by the content of photosensitizing units in the copolymer, by the kind of the counter cation of the pendant carboxylate, and the reaction medium. CH 3 CH 3 -'{ CH 2 -CH ")'~{" CH 2-C -~b 4 C" 2-CH '}~'-'~ CH 2 -C J~b COOH ~] Q COOH CH 2 -O-"(~ NO 2 OH 2-O'-(,~__~NO2 P(NPMS-MA) P(NNMS-MA)