title: Deciphering intrinsic deactivation/isomerization routes in a phytochrome chromophore model.
abstract: High level ab initio correlated (CASPT2) computations have been used to elucidate the details of the photoinduced molecular motion and decay mechanisms of a realistic phytochrome chromophore model in vacuo and to explore the reasons underneath its photophysical/photochemical properties. Competitive deactivation routes emerge that unveil the primary photochemical event and the intrinsic photoisomerization ability of this system. The emerged in vacuo based static (i.e., nondynamical) reactivity model accounts for the formation of different excited state intermediates and suggests a qualitative rationale for the short (picosecond) excited state lifetime and ultrafast decay of the emission, its small quantum yield, and the multiexponential decay observed in both solvent and phytochromes. It is thus tentatively suggested that this is a more general deactivation scheme for photoexcited phytochrome chromophores that is independent of the surrounding environment. Spectroscopic properties have also been simulated in both isolated conditions and the protein that satisfactorily match experimental data. For this purpose, preliminary hybrid QM/MM computations at the correlated (CASPT2) level have been used in the protein and are reported here for the first time.
authors: Dipartimento di Chimica G. Ciamician, Università di Bologna, Via Selmi 2, Bologna I-40126, Italy.
authors: Piero
authors: P
authors: Altoè
authors: Teresa
authors: T
authors: Climent
authors: Giulia C
authors: GC
authors: De Fusco
authors: Marco
authors: M
authors: Stenta
authors: Andrea
authors: A
authors: Bottoni
authors: Luis
authors: L
authors: Serrano-Andrés
authors: Manuela
authors: M
authors: Merchán
authors: Giorgio
authors: G
authors: Orlandi
authors: Marco
authors: M
authors: Garavelli
mesh_terms: D007536:Isomerism; D008956:Models, Chemical; D008958:Models, Molecular; D055668:Photochemical Processes; D010834:Phytochrome / Q000737:chemistry*; D011789:Quantum Theory; D013057:Spectrum Analysis; D014618:Vacuum
chemical_list: D010834:Phytochrome