title: Multistep Intersystem Crossing Pathways in Cinnamate-Based UV-B Sunscreens.
abstract: The nonradiative decay pathways of jet-cooled para-methoxy methylcinnamate (p-MMC) and para-methoxy ethylcinnamate (p-MEC) have been investigated by picosecond pump-probe and nanosecond UV-Deep UV pump-probe spectroscopy. The possible relaxation pathways were calculated by the (time-dependent) density functional theory. We found that p-MMC and p-MEC at low excess energy undergo multistep intersystem crossing (ISC) from the bright S1(1ππ*) state to the lowest triplet T1(3ππ*) state via two competing pathways through the T2state in the time scale of 100 ps: (a) stepwise ISC followed after the internal conversion (IC) from S1to the dark1nπ* state; (b) direct ISC from the S1to T2states. These picosecond multistep ISCs result in the torsion of C═C double bond by ∼95° in the T1state, whose measured adiabatic energy and lifetime are 16577 cm-1and ∼20 ns, respectively, for p-MMC. These results suggest that the ISC processes play an indispensable role in the photoprotecting sunscreens in natural plants.
authors.affiliation: Department of Chemistry, Faculty of Science, Hokkaido University , Sapporo 060-0810, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Yamazaki
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University , Higashi-Hiroshima 739-8526, Japan.
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Miyazaki
authors.affiliation: Department of Chemistry, Faculty of Science, Hokkaido University , Sapporo 060-0810, Japan.
authors.forename: Yu
authors.initials: Y
authors.lastname: Harabuchi
authors.affiliation: Department of Chemistry, Faculty of Science, Hokkaido University , Sapporo 060-0810, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Taketsugu
authors.affiliation: Department of Chemistry, Faculty of Science, Hokkaido University , Sapporo 060-0810, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Maeda
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University , Higashi-Hiroshima 739-8526, Japan.
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Inokuchi
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University , Higashi-Hiroshima 739-8526, Japan.
authors.forename: Shin-Nosuke
authors.initials: SN
authors.lastname: Kinoshita
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University , Higashi-Hiroshima 739-8526, Japan.
authors.forename: Masataka
authors.initials: M
authors.lastname: Sumida
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University , Higashi-Hiroshima 739-8526, Japan.
authors.forename: Yuuki
authors.initials: Y
authors.lastname: Onitsuka
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University , Higashi-Hiroshima 739-8526, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kohguchi
authors.affiliation: Institute for Molecular Science and Research Center for Computational Science , 38 Myodaiji, Okazaki 444-8585, Japan.|Elements Strategy for Catalysts and Batteries, Kyoto University Katsura , Kyoto 615-8520, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ehara
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University , Higashi-Hiroshima 739-8526, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Ebata