Multistep Intersystem Crossing Pathways in Cinnamate-Based UV-B Sunscreens

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

Research output: Contribution to journalArticlepeer-review

32 Citations (Scopus)


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 T2 state in the time scale of 100 ps: (a) stepwise ISC followed after the internal conversion (IC) from S1 to the dark 1nπ∗ state; (b) direct ISC from the S1 to T2 states. These picosecond multistep ISCs result in the torsion of C=C double bond by ∼95° in the T1 state, whose measured adiabatic energy and lifetime are 16577 cm-1 and ∼20 ns, respectively, for p-MMC. These results suggest that the ISC processes play an indispensable role in the photoprotecting sunscreens in natural plants.

Original languageEnglish
Pages (from-to)4001-4007
Number of pages7
JournalJournal of Physical Chemistry Letters
Issue number19
Publication statusPublished - 2016 Oct 6


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