The photolysis of phenylazotriphenyl methane (PAT) in dichloromethane and acetonitrile solution at lambda(inc) = 347 nm and at 23 degrees C results in the formation of triphenyl methyl (trityl) radicals and trityl ions. The quantum yields in dichloromethane solution are Phi(Ph(3)C(.)) = 0.060 and Phi(Ph(3)C(+)) = 0.004. Trityl ions are assumed to be formed by electron transfer between radicals formed by the photodecomposition of PAT. The yield of trityl ions is significantly increased upon irradiation of PAT solutions containing also an onium salt (N-ethoxy-2-methyl pyridinium hexafluorophosphate; (EMP(+)PF(6)(-)). This is due to the oxidation of trityl radicals by EMP(+) ions. Trityl ions generated in this way were found to be capable of initiating the cationic polymerization of cyclohexene oxide. (C) 1998 SCI.