Isomerization of the RPSB chromophore in the gas phase along the torsional pathways using QTAIM

Abstract

A QTAIM investigation of the torsion in both the clockwise and counter-clockwise directions about the π bonds of the retinal protonated Schiff base chromophore in the lowest electronically excited state provided a detailed description of the changing bonding topology that was sensitive to both the torsion and the direction of torsion. Analysis of the separate torsion calculations demonstrated a clear order of preferred bonding torsion in terms of principles of maximizing bonding. Unusual behavior of the bond ellipticity in the S1 state was found for the two less favorable bonds for torsion and explained in terms of the presence of weak bonding interactions.