Intramolecular charge transfer and photochemical isomerization in donor/acceptor-substituted butadienes

Intramolecular charge transfers, triplet state properties, and photoisomeri zation of five donor/acceptor (D/A) substituted butadienes were investigate d. Four of these derivatives (1-4) show dual fluorescence arising from a lo cally excited (LE) state and a considerably more polar intramolecular charg e transfer (ICT) state. The presence of an amino substituent with the nitro gen atom directly attached to the butadiene chain is essential for observin g dual fluorescence in this class of compounds. The compounds undergo E-Z p hotoisomerization from the excited singlet state with a quantum efficiency of about 0.1 in benzene at room temperature. The intersystem crossing effic iency for these compounds is negligible. The triplet excited-state properti es of the five butadienes have been characterized via triplet-triplet sensi tization with benzophenone as the donor.