共轭低聚物中光生分子间电荷转移态的第一性原理研究

We perform density functional theory calculations to investigate the polaron pair (charge transfer state) photo-generation in donor-acceptor oligomer methyl-capped (4,7-benzo[2,1,3]thiadiazole-2,6-(4,4-bis (2-ethylhexyl)-4H-cyclopenta[1,2-b;3,4-b'']dithiophene-4,7-benzo[2,1,3]thiadiazole)(CPDTBT).Results show that effective photo-generation of charge transfer state can happen in CPDTBT dimer when the group 4,7-benzo[2,1,3]thiadiazole (BT) in one monomer deviates against the conjugated plane (onset torsion angle is about 20°).The lower excitation energy (530 nm) can only generate the intramolecular excitonic state,while the higher excitation energy (370 nm) can generate the intermolecular charge transfer state,in good agreement with the experiment.Moreover,the mechanism of charge separation in CPDTBT oligomers is discussed.