Ab initio configuration interaction study on electronically excited 4-dimethylamino-4′-cyanostilbene

Ab initio configuration interaction calculations have been performed to examine the electronic structures of both trans-4-dimethylamino-4'-cyanostilbene (DCS) and four types of perpendicularly twisted DCSs, trans-DCS is predominantly elicited into the S-1 state out of low-lying excited states. The S-1 state is an intramolecular charge-transfer (ICT) state in which the dipole moment is about twice as large as that in S-0. The excited DCS at the 4-dimethylanilino twisted conformation, which becomes S-1 in polar solvents, has a very much larger dipole moment than that in S-1 to trans-DCS. This means that the geometrical structure of the twisted ICT (TICT) is the 4-dimethylanilino twisted form, not the dimethylamino twisted one which is well know from the TICT structure of 4-dimethylaminobenzonitrile.