Photoisomerization mechanism of the cis isomers of 1,2-distyrylbenzene and two hetero-analogues

The radiative and reactive excited state relaxations of the ZE and ZZ geometrical isomers of 1,2-distyrylbenzene [1,2-(PhE)ZB] and two hetero-analogues, where the side phenyl groups were replaced by 4'-pyridyl or 2'-thienyl groups, were studied and compared with the photobehaviour of the EE isomers previously investigated. The ZE and ZZ isomers of the hydrocarbon photoisomerize by a predominant adiabatic mechanism (a one photon - two bonds process is also operative in the case of ZZ) whereas the contribution of the adiabatic pathway is reduced for the thienyl-analogues, which isomerize by a mixed (diabatic/adiabatic) mechanism, whereas a prevalent diabatic mechanism characterizes the behaviour of the pyridyl analogue. (C) 2007 Elsevier B.V. All rights reserved.