title: Excited-state properties and environmental effects for protonated schiff bases: a theoretical study.
abstract: Complete active space self-consistent field (CASSCF), multireference configuration interaction (MRCI), density functional theory (DFT), time dependent DFT (TDDFT) and the singles and doubles coupled-cluster (CC2) methodologies have been used to study the ground state and excited states of protonated and neutral Schiff bases (PSB and SB) as models for the retinal chromophore. Systems with two to four conjugated double bonds are investigated. Geometry relaxation effects are studied in the excited pipi* state using the aforementioned methods. Taking the MRCI results as reference we find that CASSCF results are quite reliable even though overshooting of geometry changes is observed. TDDFT does not reproduce bond alternation well in the pipi* state. CC2 takes an intermediate position. Environmental effects due to solvent or protein surroundings have been studied in the excited states of the PSBs and SBs using a water molecule and solvated formate as model cases. Particular emphasis is given to the proton transfer process from the PSB to its solvent partner in the excited state. It is found that its feasibility is significantly enhanced in the excited state as compared to the ground state, which means that a proton transfer could be initiated already at an early step in the photodynamics of PSBs.
authors.affiliation: Institute for Theoretical Chemistry, University of Vienna Waehringerstrasse 17, 1090 Vienna, Austria. adelia.aquino@univie.ac.at
authors.forename: Adélia J A
authors.initials: AJ
authors.lastname: Aquino
authors.forename: Mario
authors.initials: M
authors.lastname: Barbatti
authors.forename: Hans
authors.initials: H
authors.lastname: Lischka
mesh_terms: D003198:Computer Simulation; D008956:Models, Chemical; D008958:Models, Molecular; D011522:Protons; D011789:Quantum Theory; D012168:Retinal Pigments / Q000737:chemistry; D012172:Retinaldehyde / Q000737:chemistry; D012545:Schiff Bases / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D011522:Protons; D012168:Retinal Pigments; D012545:Schiff Bases; D014867:Water; D012172:Retinaldehyde