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Multistep Intersystem Crossing Pathways in Cinnamate-Based UV-B Sunscreens
Kaoru Yamazaki1, Yasunori Miyazaki2, Yu Harabuchi1
1Department of Chemistry, Faculty of Science, Hokkaido University , Sapporo 060-0810, Japan.
The Journal of Physical Chemistry Letters
|September 23, 2016
Summary
Para-methoxy methylcinnamate (p-MMC) and ethylcinnamate (p-MEC) use multistep intersystem crossing (ISC) for rapid, non-radiative decay. This photophysical mechanism is crucial for photoprotection in plants and sunscreens.
Area of Science:
- Photochemistry
- Physical Chemistry
- Spectroscopy
Background:
- Nonradiative decay pathways are critical for understanding molecular photophysics.
- Cinnamate derivatives are relevant to natural photoprotection mechanisms.
Purpose of the Study:
- Investigate the nonradiative decay pathways of jet-cooled p-MMC and p-MEC.
- Elucidate the role of intersystem crossing (ISC) in their photophysical behavior.
Main Methods:
- Picosecond and nanosecond UV-Deep UV pump-probe spectroscopy.
- Time-dependent density functional theory (TD-DFT) calculations.
Main Results:
- Observed multistep intersystem crossing (ISC) from S1 to T1 states via T2 within 100 ps.
- Identified two competing ISC pathways: stepwise via 1nπ* and direct S1 to T2.
- Determined C═C double bond torsion of ~95° in the T1 state for p-MMC.
Conclusions:
- ISC is a key mechanism for rapid energy dissipation in p-MMC and p-MEC.
- These findings highlight the importance of ISC in the photoprotective functions of natural compounds.
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