The exchange polarization model of photoisomerization: A rationale for profound solvent effects on photoisomerization of trans-stilbene and all-trans retinal

The exchange model of photoisomerization proposed recently by us for S-1 trans-stilbene is further examined and confirmed with a set of new data on trans-stilbene-d(10). The model is then generalized (termed the exchange polarization model) in order to account for the known photoisomerization behaviors of all-trans retinal in polar and non-polar solvents, This new model gives a clear picture of how the isomerization reaction proceeds in the excited electronic state. It leads to a working hypothesis for controlling the photoisomerization pathways of polyenes.