Retinal chromophore photoinduced molecular motion and reactivity: Isolated conditions and counterion effects

Recent, work in the field of biological photoreceptors has demonstrated that computational chemistry can be successfully applied to ultrafast photobiological problems. Here we revise the results of the photoisomerization path mapping of the protonated Schiff base of retinal: the chromophore of rhodopsin proteins. These studies have produced the two-state/two-mode model which provides a rationale for the photon-induced molecular motion in the isolated retinal chromophore. Such model represents a substantial revision of the previous models for the primary event in vision in animals and light driven proton-pumping in halobacteriae. New computational results will be presented, which model the effects of an external counterfoil on the photoisomerization paths. Energetic, electronic, stereoselectivity control and tuning-effects will be analyzed and discussed in terms of counterfoil positions. Both solution and protein experimental data are revised using the new reactivity model.