Conformational relaxation dynamics in the excited electronic states of benzil in solution

Relaxation dynamics in the excited singlet (S₁) state of benzil have been studied in solution using pico and subpicosecond transient absorption spectroscopic techniques. The triple exponential decay dynamics of the S₁ state indicates that the process of conformational change from the cis-skewed to the trans-planar form takes place via the formation of a meta-stable intermediate conformer resulting the involvement of two consequent barrier crossing processes. The barrier crossing dynamics is governed by both the polarity of the solvent, which alters the barrier heights by ‘static' interactions, as well as the viscosity of the solvent via ‘dynamical' interactions.