title: Non-adiabatic dynamics investigation of the radiationless decay mechanism of trans-urocanic acid in the S2 state.
abstract: The trans-urocanic acid, a UV chromophore in the epidermis of human skin, was found to exhibit a wavelength dependent isomerization property. The isomerization quantum yield to cis-urocanic is greatest when being excited to the S1 state, whereas exciting the molecule to the S2 state causes almost no isomerization. The comparative photochemical behavior of the trans-urocanic on the S1 and S2 states continues to be the subject of intense research effort. This study is concerned with the unique photo-behavior of this interesting molecule on the S2 state. Combining the on-the-fly surface hopping dynamics simulations and static electronic structure calculations, three decay channels were observed following excitation to the S2 state. An overwhelming majority of the molecules decay to the S1 state through a planar or pucker characterized minimum energy conical intersection (MECI), and then decay to the ground state along a relaxation coordinate driven by a pucker deformation of the ring. A very small fraction of molecules decay to the S1 state by a MECI characterized by a twisting motion around the CC double bond, which continues to drive the molecule to deactivate to the ground state. The latter channel is related with the photoisomerization process, whereas the former one will only generate the original trans-form products. The present work provides a novel S2 state decay mechanism of this molecule, which offers useful information to explain the wavelength dependent isomerization behavior.
authors.affiliation: State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
authors.forename: Li
authors.initials: L
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
authors.forename: Pan-Wang
authors.initials: PW
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
authors.forename: Guang-Jiu
authors.initials: GJ
authors.lastname: Zhao
mesh_terms: D006801:Humans; D056004:Molecular Dynamics Simulation; D055668:Photochemical Processes; D012867:Skin / Q000737:chemistry; D013997:Time Factors; D014560:Urocanic Acid / Q000737:chemistry*
chemical_list: D014560:Urocanic Acid