Mechanistic study of the photolysis of ring-substituted benzyl alkanoates in methanol

The photochemistry of ring-substituted benzyl alkanoates, 1a-g and 2a-g, has been examined in methanol (MeOH). The ester conversions were substituent independent, whereas the yields of ionic products were strongly dependent. The fluorescence quantum yields and lifetimes for all methoxybenzyl esters, except para-isomers, decreased remarkably in acetonitrile (MeCN) and MeOH, Semiempirical MO calculations for the excited-state esters demonstrated that the charge densities of methylene carbon in ortho- and meta-isomers are markedly changed in the excited singlet state, which could explain the substituent dependence on the ionic product yields and the emission properties. A satisfied mechanistic interpretation of the ion formation prefers the heterolysis pathway that has been proposed by Zimmerman et al. [1-3]. (C) 2001 Elsevier Science B.V. All rights reserved.