Dynamics of cis-stilbene photoisomerization: the adiabatic pathway to excited trans-stilbene

Abstract

Fluorescence excitation spectra of cis-stilbene in n-hexane monitored at 350 nm and 404 nm, are resolved into cis-stilbene and trans-stilbene contributions using principal component analysis with self-modeling. The results confirm that both trans and cis fluorescence originating from excitation of pure cis-stilbene solutions are due to single photon excitation of 1c to 1c*. The quantum yield for adiabatic 1c*→1t* conversion is φct*=0.0020, independent of excitation wavelength. The corrected fluorescence excitation spectrum of cis-stilbene faithfully tracks its UV absorption spectrum. The fluorescence spectrum of cis-stilbene is nearly temperature independent in n-hexane, 0-58 °C. Assuming a 1c* → 1p* → 1t* pathway for adiabatic 1t* formation where 1p* is the perpendicular phantom singlet state, leads to the conclusion that 1p* and 1t* are nearly isoenergetic. © 1992.