Is photoisomerization of stilbene in solution directly promoted by solvent collisions?

TL;DR

This paper investigates whether solvent collisions directly facilitate the photoisomerization of stilbene in solution, challenging traditional theories by analyzing experimental rate behaviors that suggest a collision-promoted mechanism.

Contribution

The study provides evidence supporting the hypothesis that solvent collisions directly promote stilbene isomerization, which is a novel perspective differing from established RRKM-based explanations.

Findings

Gas phase rates follow Arrhenius law at 300 K.

Solution rates increase ten-fold and are weakly dependent on excitation wavelength.

Solvent collisions may directly promote isomerization, challenging existing theories.

Abstract

Gas phase thermal isomerization rates of trans-stilbene at 300 K obey the Arrhenius law. In solution the rates increase ten-fold and depend only very weakly on excitation wavelength or intramolecular temperature. Both observations are difficult to reconcile within RRKM theory. Previously discussed mechanisms, like restricted IVR, nonadiabaticity, solvent-dependent barriers, or excitation-induced cooling, may explain the increase of the rates in solution but not their dependence on the excitation wavelength. The latter suggests that solvent collisions can directly promote the isomerization.