Intersystem Crossing Mediated by Photoinduced Intramolecular Charge Transfer: Julolidine−Anthracene Molecules with Perpendicular π Systems
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Abstract
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 π 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 (θ1) between their π 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 θ1 ≅ 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.
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