Ab initio study on the electronic structures of stilbene at the conical intersection

Ab initio complete-active-space self-consistent-field calculations have bee n performed to examine the electronic structures of stilbene at the conical intersection. At the conformation when only the central ethylenic bond is perpendicularly twisted, the energy gap between S-0 and S-1 is too large fo r stilbene to relax into S-0. At the optimized geometry of the conical inte rsection, a covalent state with a dirdical character is energetically close to a zwitter ionic state where the electron on one of the central ethyleni c carbon atoms is transferred onto the other. (C) 1999 Elsevier Science B.V . All rights reserved.