HINDERED PHOTOISOMERIZATION OF STILBENE AT THE LIQUID SOLID INTERFACE - AN ILLUSTRATION OF COUPLED ADSORPTION REACTION PROBLEMS FOR PHYSISORBED MOLECULES

The 1B1u excited state lifetime of trans-stilbene adsorbed at the interface between liquid hexane and solid aluminum oxide has been studied using picosecond multiple light scattering techniques. A perturbation analysis of the two-flux model for transient light absorption and transient light scattering in a strongly scattering medium is presented. Application of the scattering method to stilbene isomerization shows that torsional decay at the interface is slower than in solution and is characterized by an increased activation barrier (4.7 kcal/mol) and a reduced pre-exponential factor (1.2×1012 s-1). These results are interpreted using an equation of motion for the time evolution of reactants trapped at the interface by a noncovalent adsorption potential. According to this model the change in activation energy arises from different adsorption strengths for reactant and transition state molecular structures. The change in pre-exponential factor reflects different shapes and equilibrium positions for the reactant and transition state adsorption potential functions. © 1990.