| Autor: |
Muramatsu S; Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan., Nakayama S; Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan., Kinoshita SN; Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan., Onitsuka Y; Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan., Kohguchi H; Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan., Inokuchi Y; Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan., Zhu C; Department of Applied Chemistry and Institute for Molecular Science , National Chiao Tung University , Hsinchu 30010 , Taiwan.; Center for Emergent Functional Matter Science , National Chiao Tung University , Hsinchu 30010 , Taiwan., Ebata T; Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima-shi , Hiroshima 739-8526 , Japan.; Department of Applied Chemistry and Institute for Molecular Science , National Chiao Tung University , Hsinchu 30010 , Taiwan. |
| Abstrakt: |
The title compound, 2-ethylhexyl-4-methoxycinnamate (2EH4MC), is known as a typical ingredient of sunscreen cosmetics that effectively converts the absorbed UV-B light to thermal energy. This energy conversion process includes the nonradiative decay (NRD): trans - cis isomerization and finally going back to the original structure with a release of thermal energy. In this study, we performed UV spectroscopy for jet-cooled 2EH4MC to investigate the electronic/geometrical structures as well as the NRD mechanism. Laser-induced-fluorescence (LIF) spectroscopy gave the well-resolved vibronic structure of the S 1 -S 0 transition; UV-UV hole-burning (HB) spectroscopy and density functional theory (DFT) calculations revealed the presence of syn and anti isomers, where the methoxy (-OCH 3 ) groups orient in opposite directions to each other. Picosecond UV-UV pump-probe spectroscopy revealed the NRD process from the excited singlet (S 1 ( 1 ππ*)) state occurs at a rate constant of ∼10 10 -10 11 s -1 , attributed to internal conversion (IC) to the 1 nπ* state. Nanosecond UV-deep UV (DUV) pump-probe spectroscopy identified a transient triplet (T 1 ( 3 ππ*)) state, whose energy (from S 0 ) and lifetime are 18 400 cm -1 and 20 ns, respectively. These results demonstrate that the photoisomerization of 2EH4MC includes multistep internal conversions and intersystem crossings, described as "S 1 ( trans , 1 ππ*) → 1 nπ* → T 1 ( 3 ππ*) → S 0 ( cis )". |
