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

Ab initio configuration interaction calculations have been performed to exa mine the electronic structures of both trans-4-dimethylamino-4'-cyanostilbe ne (DCS) and four types of perpendicularly twisted DCSs, trans-DCS is predo minantly 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 dipo le 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 me ans that the geometrical structure of the twisted ICT (TICT) is the 4-dimet hylanilino twisted form, not the dimethylamino twisted one which is well kn ow from the TICT structure of 4-dimethylaminobenzonitrile.