Rhodopsin (Rh) and bathorhodopsin (bathoRh) quantum-mechanics/molecular-mechanics models based on ab initio multiconfigurational wave functions are employed to look at the light induced pi-bond breaking and reconstitution occurring during the Rh -> bathoRh and bathoRh -> Rh isomerizations. More specifically, semiclassical trajectory computations are used to compare the excited (S-1) and ground (S-0) state dynamics characterizing the opposite steps of the Rh/bathoRh photochromic cycle during the first 200 fs following photoexcitation. We show that the information contained in these data provide an unprecedented insight into the sub-picosecond pi-bond reconstitution process which is at the basis of the reactivity of the protein embedded 11-cis and all-trans retinal chromophores. More specifically, the data point to the phase and amplitude of the skeletal bond length alternation stretching mode as the key factor switching the chromophore to a bonding state. It is also confirmed/found that the phase and amplitude of the hydrogen-out-of-plane mode controls the stereochemical outcome of the forward and reverse photoisomerizations.
Schapiro, Igor; Ryazantsev, Mikhail Nikolaevich; Frutos, Luis Manuel; Ferre, Nicolas; Lindh, Roland; and Olivucci, Massimo, "The Ultrafast Photoisomerizations Of Rhodopsin And Bathorhodopsin Are Modulated By Bond Length Alternation And Hoop Driven Electronic Effects" (2011). Chemistry Faculty Publications. 68.
Journal Of The American Chemical Society