Adiabatic Potential for cis-trans Isomerization of Rhodopsin Chromophore in the Deformed Excited State

On the protonated retinal Schiff-base (PRSB) interacting with counter point charge e , the adiabatic potential for cis-trans isomerization of the first singlet excited-state is calculated as a function of rotation angle θ 11-12 about C 11 -C 12 bond, including the effects of the deformation in geometrical structure of the excited state after the absorption of light. It is shown that the potential curve of this deformed excited state is barrierless and downward concave whereas that of the ground state is upward convex, and that the two curves intersect in the vicinity of θ 11-12 =90°. It is also shown that, in the highly twisted conformation at θ 11-12 =90°, the deformed excited state is considerably polarized with almost positive charge | e | shifted into C 12 -N + 16 fragment, so that the effect of e on the adiabatic potential of the deformed excited state is important.