Experimental and theoretical study on the excited-state dynamics of ortho-, meta-, and para-methoxy methylcinnamate

Miyazaki Yasunori

Yamamoto Kanji

Aoki Jun

Ikeda Toshiaki

Inokuchi Yoshiya

Ehara Masahiro

Ebata Takayuki

The Journal of Chemical Physics

The S1 state dynamics of methoxy methylcinnamate (MMC) has been investigated under supersonic jet-cooled conditions. The vibrationally resolved S1-S0 absorption spectrum was recorded by laser induced fluorescence and mass-resolved resonant two-photon ionization spectroscopy and separated into conformers by UV-UV hole-burning (UV-UV HB) spectroscopy. The S1 lifetime measurements revealed different dynamics of para-methoxy methylcinnamate from ortho-methoxy methylcinnamate and meta-methoxy methylcinnamate (hereafter, abbreviated as p-, o-, and m-MMCs, respectively). The lifetimes of o-MMC and m-MMC are on the nanosecond time scale and exhibit little tendency of excess energy dependence. On the other hand, p-MMC decays much faster and its lifetime is conformer and excess energy dependent. In addition, the p-MMC-H2O complex was studied to explore the effect of hydration on the S1 state dynamics of p-MMC, and it was found that the hydration significantly accelerates the nonradiative decay. Quantum chemical calculation was employed to search the major decay route from S1(ππ*) for three MMCs and p-MMC-H2O in terms of (i) trans → cis isomerization and (ii) internal conversion to the 1nπ* state. In o-MMC and m-MMC, the large energy barrier is created for the nonradiative decay along (i) the double-bond twisting coordinate (～1000 cm-1) in S1 as well as (ii) the linear interpolating internal coordinate (～1000 cm-1) from S1 to 1nπ? states. The calculation on p-MMC decay dynamics suggests that both (i) and (ii) are available due to small energy barrier, i.e., 160 cm-1 by the double-bond twisting and 390 cm-1 by the potential energy crossing. The hydration of p-MMC raises the energy barrier of the IC route to the S1/1nπ* conical intersection, convincing that the direct isomerization is more likely to occur.

Chemistry [ 430 ]

eng

American Institute of Physics

Copyright (c) 2014 AIP Publishing LLC.

[ISSN] 0021-9606

[DOI] 10.1063/1.4904268

[DOI] http://dx.doi.org/10.1063/1.4904268 isVersionOf