Theoretical Studies of Photoisomerization in Visual Pigments. II. Numerical Calculation

Abstract

A general theory of the non-adiabatic multiphonon relaxation rate, which was developed in the preceding paper, was applied to the photoisomerization of visual pigments. We estimated the free energy relation among rhodopsin, bathorhodopsin, common state and transition state of thermal isomerization. We calculated microscopic parameters such as a displacement of the normal coordinate due to the transition and electronic coupling matrix element. We investigated how the non-radiative transition rate varies with the free energy gap. We analyzed molecular mechanisms which made photoisomerization of visual pigments very rapid compared with that of other organic molecules. It was clarified that the matching condition which corresponds to the maximum Franck-Condon overlap is almost satisfied in visual systems and it is the main reason for the very rapid non-radiative transition.