title: Mechanistic Photochemistry of Methyl-4-hydroxycinnamate Chromophore and Its One-Water Complexes: Insights from MS-CASPT2 Study.
abstract: Herein we computationally studied the excited-state properties and decay dynamics of methyl-4-hydroxycinnamate (OMpCA) in the lowest three electronic states, that is, (1)ππ*, (1)nπ*, and S0 using combined MS-CASPT2 and CASSCF electronic structure methods. We found that one-water hydration can significantly stabilize and destabilize the vertical excitation energies of the spectroscopically bright (1)ππ* and dark (1)nπ* excited singlet states, respectively; in contrast, it has a much smaller effect on the (1)ππ* and (1)nπ* adiabatic excitation energies. Mechanistically, we located two (1)ππ* excited-state relaxation channels. One is the internal conversion to the dark (1)nπ* state, and the other is the (1)ππ* photoisomerization that eventually leads the system to a (1)ππ*/S0 conical intersection region, near which the radiationless internal conversion to the S0 state occurs. These two (1)ππ* relaxation pathways play distinct roles in OMpCA and its two one-water complexes (OMpCA-W1 and OMpCA-W2). In OMpCA, the predominant (1)ππ* decay route is the state-switching to the dark (1)nπ* state, while in one-water complexes, the importance of the (1)ππ* photoisomerization is significantly enhanced because the internal conversion to the (1)nπ* state is heavily suppressed due to the one-water hydration.
authors.affiliation: Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University , Beijing 100875, China.
authors.forename: Xiao-Ying
authors.initials: XY
authors.lastname: Xie
authors.affiliation: Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University , Beijing 100875, China.
authors.forename: Chun-Xiang
authors.initials: CX
authors.lastname: Li
authors.affiliation: Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University , Beijing 100875, China.
authors.forename: Qiu
authors.initials: Q
authors.lastname: Fang
authors.affiliation: Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University , Beijing 100875, China.
authors.forename: Ganglong
authors.initials: G
authors.lastname: Cui