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

Ab initio complete-active-space self-consistent-field calculations have been 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 for stilbene to relax into S-0. At the optimized geometry of the conical intersection, a covalent state with a dirdical character is energetically close to a zwitter ionic state where the electron on one of the central ethylenic carbon atoms is transferred onto the other. (C) 1999 Elsevier Science B.V. All rights reserved.