Dynamics of the photoinduced ring-opening of stilbene, a prototypical diarylethene

Simulations of the photoconversion of 4a,4b-dihydrophenanthrene (DHP) to stilbene, using semiclassical electron-radiation-ion dynamics, are reported. The carbon single bond connecting the phenyl rings breaks approximately 200 fs after the laser pulse is turned off. The excited cis-stilbene molecule, then further isomerizes to the trans conformation after about 1 ps. Each of these two changes of molecular geometry involves a HOMO-LUMO avoided crossing, which produces a transfer of electronic population from LUMO to HOMO. These detailed dynamical simulations are thus consistent with the interpretation that ring-opening in stilbene is a single photon process.