1. Y. Miyazaki, K. Yamamoto, J. Aoki, T. Ikeda, Y. Inokuchi, M. Ehara and T. Ebata, J.
Chem. Phys., 2014, 141, 244313.
2. K. M. Krokidi, M. A. P. Turner, P. A. J. Pearcy and V. G. Stavros, Mol. Phys., 2020,
DOI: 10.1080/00268976.2020.1811910.
3. E. M. M. Tan, M. Hilbers and W. J. Buma, J. Phys. Chem. Lett., 2014, 5, 2464-2468.
4. E. M. M. Tan, S. Amirjalayer, B. H. Bakker and W. J. Buma, Faraday Discuss., 2013,
163, 321-340.
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Chapter 6
Conclusion of this thesis
In this thesis, the substitution and hydrogen (H)-bonding effects on the electronic
states and the nonradiative decay (NRD) route involving trans (E) → cis (Z)
photoisomerization of methylcinnamate (MC) were investigated by supersonic
jet/laser spectroscopy and quantum chemical calculation. Finally, this thesis aims
to provide a molecular design for a development of cinnamate-based sunscreen.
In Chapter 3, the photoisomerization of non-substituted cinnamate, MC,
was investigated. In the electronic spectra of jet-cooled MC, the optically “dark”
nπ* state was observed in the energy region lower than the optically “blight” 1ππ*
state. Upon photoexcitation to the 1ππ* state, trans-MC rapidly decays to the 1nπ*
state via internal conversion (IC). After the IC, MC decays to the T1 (3ππ*) via
consecutive intersystem crossing and ICs. Finally, MC either returns to transisomer or isomerizes to cis-isomer in the ground state (S0). Therefore, it is
concluded that the dominant photoisomerization route of MC is described as
“1ππ* (trans) → 1nπ* → T1 (3ππ*) → S0 (trans or cis)”.
In Chapter 4, the substitution and its position effect on the
photoisomerization of MC was investigated. The substitution at para position
slightly lowers the energy of the 1ππ* state, therefore order of the 1ππ* and 1nπ*
states is reversed between MC and para-substituted MCs. This energy inversion
143
increases the contribution of another sub ns NRD route involving the T1 state that
is described as “1ππ* (trans) → 3nπ* → 3ππ* → S0 (trans or cis)”. On the other
hand, the substitution at meta or ortho position drastically lowers the energy of
the 1ππ* state and increases the energy barrier of 1ππ* → 1nπ* IC. Thus, the direct
isomerization process, twisting of the C=C bond on the 1ππ* potential energy
surface (PES), is thought to be the dominant photoisomerization route, described
as “1ππ* (trans) → C=C bond twisting on the 1ππ* PES → S0 (trans or cis)”. The
electronic state and NRD/photoisomerization of cinnamates are affected by the
substitution at its phenyl ring. para-substituted cinnamates can be the most
effective sunscreen reagents because the multistep NRD process can rapidly
convert harmful absorbed UV energy to safer thermal energy.
In Chapter 5, the H-bonding effect on the NRD process of MC was
investigated. The H-bonding of a methanol molecule to the C=O group in MC
suppresses the 1ππ* → 1nπ* IC and generation of the T1 (3ππ*). This result consists
with that in solution, that the fluorescence intensity of MC in methanol is two
times larger than that in cyclohexane.
Finally, the newly developed nanosecond UV-tunable DUV pump-probe
spectroscopy is versatile, therefore this spectroscopy can be applied to other
systems. Thus, I strongly believe that this new spectroscopy reveals the NRD
process of other sunscreen reagents shown in Chapter 1 and helps us to design
more effective chemical filter in the future.
144
145
බ⾲ㄽᩥ
(1) Substitution effect on the nonradiative decay and trans → cis
photoisomerization route: a guideline to develop efficient cinnamate based
sunscreens
Shin-nosuke Kinoshita, Yu Harabuchi, Yoshiya Inokuchi, Satoshi Maeda,
Masahiro Ehara, Kaoru Yamazaki and Takayuki Ebata
Phys. Chem. Chem. Phys., 2021,23, 834-845.
Front cover picture, 2021 PCCP HOT Articles
(2) The direct observation of the doorway 1nπ* state of methylcinnamate and
hydrogen-bonding effects on the photochemistry of cinnamate-based
sunscreens
Shin-nosuke Kinoshita, Yoshiya Inokuchi, Yuuki Onitsuka, Hiroshi Kohguchi,
Nobuyuki Akai, Takafumi Shiraogawa, Masahiro Ehara, Kaoru Yamazaki, Yu
Harabuchi, Satoshi Maeda and Takayuki Ebata
Phys. Chem. Chem. Phys., 2019, 21, 19755-19763.
Back cover picture, 2019 PCCP HOT Articles
(3) Different photoisomerization routes found in the structural isomers of
hydroxy methylcinnamate
Shin-nosuke Kinoshita, Yasunori Miyazaki, Masataka Sumida, Yuuki Onitsuka,
Hiroshi Kohguchi, Yoshiya Inokuchi, Nobuyuki Akai, Takafumi Shiraogawa,
Masahiro Ehara, Kaoru Yamazaki, Yu Harabuchi, Satoshi Maeda, Tetsuya
Taketsugu and Takayuki Ebata
Phys. Chem. Chem. Phys., 2018, 20, 17583-17598.
Back cover picture
146
ཧ⪃ㄽᩥ
(1) Electronic States and Nonradiative Decay of Cold Gas-Phase Cinnamic
Acid Derivatives Studied by Laser Spectroscopy with Laser Ablation
Technique
Yuji Iida, Shin-nosuke Kinoshita, Seiya Kenjo, Satoru Muramatsu, Yoshiya
Inokuchi, Chaoyuan Zhu, and Takayuki Ebata
J. Phys. Chem. A 2020, 124, 5580-5589.
(2) Electronic State and Photophysics of 2-Ethylhexyl-4-methoxy cinnamate
as UV-B Sunscreen under Jet-Cooled Condition
Satoru Muramatsu, Shingo Nakayama, Shin-nosuke Kinoshita, Yuuki Onitsuka,
Hiroshi Kohguchi, Yoshiya Inokuchi, Chaoyuan Zhu, and Takayuki Ebata
J. Phys. Chem. A 2020, 124, 1272-1278.
(3) Laser spectroscopic study on sinapic acid and its hydrated complex in a
cold gas phase molecular beam
Seiya Kenjo, Yuji Iida, Nobumasa Chaki, Shin-nosuke Kinoshita, Yoshiya
Inokuchi, Kaoru Yamazaki, Takayuki Ebata
Chemical Physics 515 (2018) 381-386.
(4) 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, and Takayuki Ebata
J. Phys. Chem. Lett. 2016, 7, 4001-4007.
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