title: Tracking the excited-state time evolution of the visual pigment with multiconfigurational quantum chemistry.
abstract: The primary event that initiates vision is the photoinduced isomerization of retinal in the visual pigment rhodopsin (Rh). Here, we use a scaled quantum mechanics/molecular mechanics potential that reproduces the isomerization path determined with multiconfigurational perturbation theory to follow the excited-state evolution of bovine Rh. The analysis of a 140-fs trajectory provides a description of the electronic and geometrical changes that prepare the system for decay to the ground state. The data uncover a complex change of the retinal backbone that, at approximately 60-fs delay, initiates a space saving "asynchronous bicycle-pedal or crankshaft" motion, leading to a conical intersection on a 110-fs time scale. It is shown that the twisted structure achieved at decay features a momentum that provides a natural route toward the photoRh structure recently resolved by using femtosecond-stimulated Raman spectroscopy.
authors.affiliation: Dipartimento di Chimica, Università di Siena, via Aldo Moro 2, I-53100 Siena, Italy.
authors.forename: Luis Manuel
authors.initials: LM
authors.lastname: Frutos
authors.forename: Tadeusz
authors.initials: T
authors.lastname: Andruniów
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Santoro
authors.forename: Nicolas
authors.initials: N
authors.lastname: Ferré
authors.forename: Massimo
authors.initials: M
authors.lastname: Olivucci
mesh_terms: D008432:Mathematical Computing; D008958:Models, Molecular; D015394:Molecular Structure; D011789:Quantum Theory; D012243:Rhodopsin / Q000737:chemistry*; D013059:Spectrum Analysis, Raman
chemical_list: D012243:Rhodopsin