Photochemistry in a Heterogenous System: Chlorophyll-Sensitized Reduction of p-Dinitrobenzene by Hydrazobenzene

Article abstract of DOI:10.1021/j100286a037

The photoreduction of p-dinitrobenzene, sensitized by aqueous suspensions of chlorophyll a with other amphiphiles adsorbed onto polyethylene-tetradecane particles, differs in some respects from the photoreduction in solution.The reaction proceeds in two stages.The products of the first stage, N-(p-nitrophenyl)hydroxylamine and azobenzene, are separated into the aqueous and hydrocarbon particles phases, respectively.The nature of the second stage of reaction is uncertain, but observations are best explained by a reduction of N-(p-nitrophenyl)hydroxylamine to 4,4'-dinitrohydrazobenzene.The quantum yield of photoreduction to the hydroxylamine does not seem to correlate at all with the quantum yield of fluorescence of the sensitizing particles.This and the relative magnitudes of the yields suggest that the principal photochemical reaction is reduction of dinitrobenzene not by the excited singlet state of chlorophyll or by the triplet state formed directly by intersystem crossing but by high-energy ion pair states or perhaps triplets formed from them by decay.Absorption spectrometry in the heterogeneous system is complicated by superposition of the so-called sieve effect on the path-lenth enhancement effect of the highly scattering system.The role of the interface between the particle and aqueous phases on the course of the reaction is discussed.