SUBSTITUTED PHTHALOCYANINE-SENSITIZED PHOTOCHEMICAL GENERATION OF SUPEROXIDE ANION-RADICAL

The quantum yield of phthalocyanine-photosensitized generation of superoxide anion radical (O-2(-)) was measured by the electron spin resonance (ESR) technique. From the redox potential data, it is concluded that O-2(-) is formed by electron transfer from the singlet excited state (not triplet or ground state) of phthalocyanines (PCs) to oxygen. Since a much larger theoretical quantum yield of O-2(-) generation (Phi(c)) than experimental (Phi(m)) was found, it is suggested that charge recombination processes between O-2(-) and PCsdivided by occur more rapidly than O-2(-) trapping by 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). The results indicate that the use of DMPO as a spin trap is not an ideal method for measurement of the quantity of O-2(-) formed via photosensitization.