Different photoisomerization routes found in the structural isomers of hydroxy methylcinnamate

Shin Nosuke Kinoshita, Yasunori Miyazaki, Masataka Sumida, Yuuki Onitsuka, Hiroshi Kohguchi, Yoshiya Inokuchi, Nobuyuki Akai, Takafumi Shiraogawa, Masahiro Ehara, Kaoru Yamazaki, Yu Harabuchi, Satoshi Maeda, Tetsuya Taketsugu, Takayuki Ebata

研究成果: ジャーナルへの寄稿学術論文査読

21 被引用数 (Scopus)


An experimental and theoretical study has been carried out to elucidate the nonradiative decay (NRD) and trans(E) → cis(Z) isomerization from the S1 (1ππ∗) state of structural isomers of hydroxy methylcinnamate (HMC); ortho-, meta- and para-HMC (o-, m- and p-HMC). A low temperature matrix-isolation Fourier Transform Infrared (FTIR) spectroscopic study revealed that all the HMCs are cis-isomerized upon UV irradiation. A variety of laser spectroscopic methods have been utilized for jet-cooled gas phase molecules to investigate the vibronic structure and lifetimes of the S1 state, and to detect the transient state appearing in the NRD process. In p-HMC, the zero-point level of the S1 state decays as quickly as 9 ps. A transient electronic state reported by Tan et al. (Faraday Discuss. 2013, 163, 321-340) was reinvestigated by nanosecond UV-tunable deep UV pump-probe spectroscopy and was assigned to the T1 state. For m- and o-HMC, the lifetime at the zero-point energy level of S1 is 10 ns and 6 ns, respectively, but it becomes substantially shorter at an excess energy higher than 1000 cm-1 and 600 cm-1, respectively, indicating the onset of NRD. Different from p-HMC, no transient state (T1) was observed in m- nor o-HMC. These experimental results are interpreted with the aid of TDDFT calculations by considering the excited-state reaction pathways and the radiative/nonradiative rate constants. It is concluded that in p-HMC, the trans → cis isomerization proceeds via a [trans-S11nπ∗ → T1 → cis-S0] scheme. On the other hand, in o- and m-HMC, the isomerization proceeds via a [trans-S1 → twisting along the CC double bond by 90° on S1 → cis-S0] scheme. The calculated barrier height along the twisting coordinate agrees well with the observed onset of the NRD channel for both o- and m-HMC.

ジャーナルPhysical Chemistry Chemical Physics
出版ステータス出版済み - 2018


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