On the Role of the Change in Bond Lengths in the Photoisomerization of Rhodopsin Chromophore

Abstract

On the π-electron system of PRSB with its counter point-charge, we consider such “deformed” excited state that has different bond lengths for stabilization from those in the excited state immediately after the absorption of light, together with “virtual” ground state having the same bond lengths as the deformed excited state. And we calculate their adiabatic potentials and net-charge distributions for the respective cases of cis-trans isomerization around single and double bonds. It is shown that a close approach of adiabatic potentials between the deformed excited and virtual ground states occurs only in the case around C₁₁–C₁₂ bond, and that only the case around C₁₁–C₁₂ or C₁₃–C₁₄ bond generates a rapid reciprocating motion (a large transient polarization) of net charges in the deformed excited state (in the virtual ground state in the region of the orthogonal conformation).