Strong vibronic interactions and possible electron pairing in the photoinduced excited electronic states in nanosized molecules

Electron–phonon interactions in the photoinduced excited electronic states are investigated, and compared with those in the monoanionic and monocationic electronic states in acenes. The total electron–phonon coupling constants for the monoanionic (lLUMO), monocationic (lHOMO), and photoinduced excited electronic states ( l B 1 u ( HOMO → LUMO ) ) in acenes are estimated. The l B 1 u ( HOMO → LUMO ) values are much larger than the lLUMO and lHOMO values in acenes. The complete phase patterns difference between the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) in acenes, are the main reason why the C–C stretching modes around 1500 cm−1 afford much larger electron–phonon coupling constants in the photoinduced excited electronic states than in the monoanionic and monocationic electronic states in acenes, and the reason why the l B 1 u ( HOMO → LUMO ) values are much larger than the lLUMO and lHOMO values in acenes.