A study of the photoionization of anion radicals in aqueous solution

Abstract

The photolysis of a number of radical anions of substituted aromatic carboxylic acids has been investigated by two-pulse experiments using pulse radiolysis and laser photolysis. The aim of the study is to determine the photophysical and photochemical processes that follow optical excitation of these radicals. Photoionization with varying quantum efficiencies from 0.4 for benzoate dianion radical to <0.01 for anion radicals of formyl-, acetyl-, and benzoylbenzoic acids is found to be the only process in all but a few special cases. In no case was luminescence of the radical observed. The quantum yields seem to be strongly affected by structural factors even when the energetics are favorable. Because the radicals selected for study absorb in the visible region, it has thus been possible to examine the process of charge separation with photons of a much lower energy than is necessary for most normal molecules. It is hoped these results may provide insights that will be of value in the design of systems to provide useful conversion of solar energy.