Browsing by Author "Ebata, Takayuki"

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Electronic State and Photophysics of 2-Ethylhexyl-4-methoxycinnamate as UV-B Sunscreen under Jet-Cooled Condition
(2020-02-20)
Muramatsu, Satoru
;
Nakayama, Shingo
;
Kinoshita, Shin-nosuke
;
Onitsuka, Yuuki
;
Kohguchi, Hiroshi
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 (HE) spectroscopy and density functional theory (DFT) calculations revealed the presence of syn and anti isomers, where the methoxy (-OCH3) 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)pi pi*)) state occurs at a rate constant of similar to 10(10)-10(11) s(-1), attributed to internal conversion (IC) to the (1)n pi* state. Nanosecond UV-deep UV (DUV) pumpprobe spectroscopy identified a transient triplet (T-1 ((3)pi pi*)) 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)pi pi*) -> (1)n pi* -> T-1 ((3)pi pi* -> S-0 (cis)".
Electronic States and Nonradiative Decay of Cold Gas-Phase Cinnamic Acid Derivatives Studied by Laser Spectroscopy with a Laser-Ablation Technique
(2020-07-09)
Iida, Yuji
;
Kinoshita, Shin-nosuke
;
Kenjo, Seiya
;
Muramatsu, Satoru
;
Inokuchi, Yoshiya
We performed UV spectroscopy for p-coumaric acid (pCA), ferulic acid (FA), and caffeic acid (CafA) under jet-cooled gas-phase conditions by using a laser-ablation source. These molecules showed the S-1((1)pi pi*)-S-0 absorption in the 31 500-33 500 cm(-1) region. Both pCA and FA exhibited sharp vibronic bands, while CafA showed only a broad feature. The decay time profile of the (1)pi pi* state was measured by picosecond pump-probe spectroscopy, and the transient state produced through the nonradiative decay (NRD) from (1)pi pi* and its time profile were measured by nanosecond UV-deep UV pump-probe spectroscopy. The transient state was observed for pCA and FA and assigned to the T-1 state, and we concluded that the NRD process of (1)pi pi* is S-1((1)pi pi*). (1)n pi* -> T-1((3)pi pi*), similar to those of methyl cinnamate and para-substituted cinnamates such as p-hydroxy and p-methoxy methyl cinnamate. On the other hand, the transient T-1 state was not detected in CafA, and its NRD route is suggested to be S-1((1)pi pi*). (1)pi sigma* -> H atom elimination, similar to those of phenol and catechol. The effect of a hydrogen bond on the electronic state and NRD process was investigated, and it was found that the H-bonding lowers the (1)pi pi* energy and suppresses the NRD process for all the species.