Photochemistry of substituted methyl-α-arylcinnamates:: ortho- and para-substitution

The 308 nm laser photochemistry of a series of substituted methyl-alpha-arylcinnamates has been studied in deoxygenated hexane and acetonitrile. Methyl-alpha-phenylcinnamate (1a) and derivatives that are p-substituted with electron withdrawing (chloro, Ib) or electron donating (methoxy, Ic) groups exhibited very similar photochemistry and spectroscopic properties, with the photostationary state (pss) composition ([E]/[Z]) being. on the average, 2.8 for these substances. By contrast the pss value for the o,o-dichloro substituted arylcinnamate (Id) was found to be only 0.5. This difference is discussed in terms of possible influences of the o,o-dichloro substituents on the excited state potential energy surface for arylcinnamate photoisomerization. (C) 1998 Elsevier Science S.A. All rights reserved.