VISUAL PIGMENTS: THEIR SPECTRA AND ISOMERIZATIONS*

Abstract

Abstract— We have made Pariser‐Parr‐Pople molecular orbital calculations of the torsional energy curves for rotation about pertinent bonds in retinal and its Schiffs base derivatives. The results correlate well with their observed spectra and isomerization behavior. The calculations are also consistent with the visual pigment model of a protonated Schiffs base of retinal perturbed by a charged group in its environment.