Intersystem Crossing Mediated by Photoinduced Intramolecular Charge Transfer:  Julolidine−Anthracene Molecules with Perpendicular Systems.

Time-resolved electron paramagnetic resonance studies show that the primary mechanism of triplet formation following photoexcitation of julolidine-anthracene molecules linked by a single bond and having perpendicular systems is a spin−orbit, charge-transfer intersystem crossing mechanism (SOCT−ISC). This mechanism depends on the degree of charge transfer from julolidine to anthracene, the dihedral angle (1) between their systems, and the magnitude of the electronic coupling between julolidine and anthracene. We compare 4-(9-anthracenyl)-julolidine with the more sterically encumbered 4-(9-anthracenyl)-3,5-dimethyljulolidine and find that fixing 1≅ 90° serves to enhance SOCT−ISC by increasing the change in orbital angular momentum accompanying charge transfer. Given that the requirements for the SOCT−ISC mechanism are quite general, we expect it to occur in a variety of electron donor−acceptor systems. [ABSTRACT FROM AUTHOR]