Dynamical Theory of Photoisomerization of the Rhodopsin Chromophore: Generation of a Transient Electric Field during Photoisomerization

Abstract

Photoisomerization of the rhodopsin chromophore is one of the typical nonadiabatic transitions. We have proposed a new dynamical theory of photoisomerization of the chromophore based on quantum mechanics. We have considered the transient excited state DES (deformed excited state: ΨD) of electrons, which has different lengths for stabilization from those in the excited state immediately after the absorption of light, together with the lowest electronic state VGS (virtual ground state: ΨV), which has the same bond lengths as ΨD. We have also considered the normal vibrational states {Urj(ϑ)} associated with these transient electronic states {Ψr(ϑ)} (ϑ represents the angle of cis−trans isomerization). With these preliminary assumptions, the nonstationary state Φ(t) of the chromophore has been expressed as an expansion in {Ψr(ϑ)Urj(ϑ)}, and the time-dependent equation for its coefficients {brj(t)} has been derived rigorously by explicitly taking into account the kinetic energy of atomic cores. On these bases...