title: Photoisomerization mechanism of 1,1'-dimethyl-2,2'-pyridocyanine in the gas phase and in solution.
abstract: The trans→cis and cis→trans photoisomerization mechanisms of 1,1'-dimethyl-2,2'-pyridocyanine have been investigated theoretically in the gas phase and in methanol. Two-dimensional potential energy surfaces were computed for the ground and first excited singlet states of the isolated molecule using complete active space self-consistent field method. Our computations suggest that the torsion around the central C-C bonds with carbon-out-of-plane motion is the preferred photoisomerization mechanism. In the gas phase, conical intersections were found near the minima of excited state. The excited-state decay follows a barrierless minimum-energy pathway before the molecule moves to the excited-state global minimum (minS1) and the system relaxes to the ground state through a conical intersection. In methanol, the system would first reach a stationary structure of C2 symmetry after the trans form is electronically excited. Solvent polarity effects were investigated in chloroform, dichloromethane, 1-propanol, ethanol, methanol, and water. There is a significant barrier between the stationary structure of C2 symmetry and minS1 in the excited state in high polarity solvents. Thus, Me-1122P has a much longer lifetime of the excited state in solvents of high polarity.
authors.affiliation: State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China; Graduate School of the Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Aihua
authors.initials: A
authors.lastname: Gao
authors.affiliation: State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
authors.forename: Peiyu
authors.initials: P
authors.lastname: Zhang
authors.affiliation: Institute of Theoretical Simulation Chemistry, Academy of Fundamental and Interdisciplinary Science, Harbin Institute of Technology, Harbin 150080, China.
authors.forename: Meiyu
authors.initials: M
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China. Electronic address: beam@dicp.ac.cn.
authors.forename: Jianyong
authors.initials: J
authors.lastname: Liu
mesh_terms: D002232:Carbocyanines / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D007536:Isomerism; D008027:Light; D000432:Methanol / Q000737:chemistry; D008968:Molecular Conformation; D011725:Pyridines / Q000737:chemistry*; D012996:Solutions; D012997:Solvents / Q000737:chemistry; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D002232:Carbocyanines; D005740:Gases; D011725:Pyridines; D012996:Solutions; D012997:Solvents; D000432:Methanol
keywords: 1,1′-Dimethyl-2,2′-pyridocyanine; Conical intersection; PES; Photochemical; Photoisomerization