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

Intramolecular charge transfers, triplet state properties, and photoisomerization of five donor/acceptor (D/A) substituted butadienes were investigated. Four of these derivatives (1-4) show dual fluorescence arising from a locally excited (LE) state and a considerably more polar intramolecular charge transfer (ICT) state. The presence of an amino substituent with the nitrogen atom directly attached to the butadiene chain is essential for observing dual fluorescence in this class of compounds. The compounds undergo E-Z photoisomerization from the excited singlet state with a quantum efficiency of about 0.1 in benzene at room temperature. The intersystem crossing efficiency for these compounds is negligible. The triplet excited-state properties of the five butadienes have been characterized via triplet-triplet sensitization with benzophenone as the donor.