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Cationic photopolymerization of epoxides by the direct and sensitized photolysis of eight onium tetrakis(pentafluorophenyl)borates as initiators has been investigated. The relative reactivity of the onium borates on the photopolymerization was studied by the measurement of spectral sensitivity and by real time Fourier transform infrared spectroscopy. The kinetics of the photopolymerization by the sensitized photolysis was different from that of the direct photolysis. Several onium borates were sensitized by the excited singlet state of the anthracenes (nonsubstituted anthracene and 9-methyl- and 9,10-dimethylanthracene), and the rates of polymerization increased with decreasing free energy changes between the onium borates and the excited singlet state of 9-methylanthracene. The acid generated by the photodecomposition of the onium borates produced nonacidic products by heating.

Donor−acceptor initiators, onium butyltriphenylborates (DPIB, DMPSB) containing both an onium cation (electron-accepting radical generator) and a borate anion (electron-donating radical generator) within the same compound were able to be sensitized by two aromatic ketones (2-chlorothioxanthone and Michler's ketone) to initiate polymerization of tetrahydrofurfuryl acrylate monomer. The photopolymerization efficiency of the onium butyltriphenylborates was higher than that of the onium salts (DPI, DMPS) or the borate compound (TBAB). The photoinitiation processes between the photosensitizers and the initiators have been investigated by laser flash photolysis. It has been clarified that two kinds of radical species are generated by a photoinduced electron-transfer mechanism.

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Photochemical reactions between the excited triplet state of C60 and the ion-pair charge-transfer complex which consists of electron-acceptor cation (methyl viologen (MV2+)) and electron-donor anion (organo borates (-BPh3R, where R = Ph or Bu)) have been investigated by both steady-state and laser-flash photolysis. By photoirradiation of C60 in the presence of MV2+(-BPh3R)2 in organic solvents, the amount of MV+• increases with irradiation time, and persists for a long time even in the dark. From the laser-flash photolysis, it is found that electron transfer proceeds via 3C60* from -BPh3R in the complex, yielding •BPh3R and C60 -•. Although generated C60 -• does not decay in the absence of MV2+ because of the rapid dissociation of •BPh3R, in the presence of MV2+, C60 -• decays quickly by transferring an electron to MV2+ yielding MV+•. Thus, it is proved that C60 acts as a photosensitizer for pumping up an electron from -BPh3R as well as an electron mediator to MV2+. In these systems, MV+• persists even in air-saturated solution for more than an hour, suggesting that the electron transfer from MV+• to O2 is retarded.