Ab initio study on the photochemical behavior of 4-dimethylamino,4′-cyanostilbene

Ab initio complete active space self-consistent field (CASSCF) and the second order perturbation (MRMP2) calculations have been performed to examine the photochemical behavior of 4-dimethylamino,4'-cyanostilbene (DCS) in the low-lying excited states, The potential energy curves with respect to four torsional angles at the CASSCF level is possible to give a reasonable interpretation on the experimental findings and the MRMP2 calculation well reproduces the experimental observable such as the excitation energy. The S-1 state in the Franck-Condon region is the internal charge transfer (ICT) state where the electron is partially transferred from the 4-dimethylanilino into the 4-cyanostyryl groups. Only the potential energy curve in S-1 with respect to the torsional motion of the ethylenic double bond has a small barrier to the perpendicularly twisted conformation leading to the cis-trans photoisomerization, though the others becomes energetically much unstable. DCS in S-1 in polar solvent is, on the other hand, stabilized by the torsional motion of the 4-dimethylanilino group. (C) 2001 Elsevier Science B.V. All rights reserved.