1. Nonradiative Decay Route of Cinnamate Derivative studied by 　Frequency and Time Domain Laser Spectroscopy in the gas phase, Matrix Isolation FTIR Spectroscopy and Quantum Chemical Calculations
TAKAYUKI EBATA, Yasunori Miyazaki, Sin-nosuke Kinoshita, Masataka Sumida, Yuuki Onitsuka, Hiroshi Kohguchi, Yoshiya Inokuchi, Hiroshima University
Nobuyuki Akai, Tokyo University of Agriculture and Technology
Masahiro Ehara, Institute for Molecular Science
Kaoru Yamazaki, Yu Harabuchi, Tetsuya Taketsugu, Satoshi Maeda, Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, Japan

2. trans → cis isomerization of cinnamate derivative
Plant and in our life
Building blocks of lignin for cell wall (Lignin)
Protection against sunlight (UV) →　cosmetic use
Bacteria
Trigger of negative phototaxis (PYP chromophore)
p-MMC
Mechanism of NR process leading to isomerization
1 . Double-bond twist in the S1(ππ*) state
2. S1(ππ*)→ 1nπ* Internal conversion 1 2

3. Investigation of the dark sate
Possibility 2 : S1(ππ*)→ 1nπ* Internal conversion
Picosecond UV+ UV’ pump-probe
pMMC
Miyazaki et al., J. Chem. Chem., (2014)
Nanosecond UV+ 193 nm pump-probe
193 nm
1np*
pMMC
τ = 17.7 ns
Tan et al., J. Phys. Chem. Letter, 5, 2464 (2014)
The dark sate could be 1np* and
the state can be observed only in monomer

4. Assignment of the dark state (1np*?)
R2PI spectrum of p-MMC
Black: n1 only
Red: n1 + DUV (Dt= 10 ns)
Ion intensity
syn / s-cis
syn / s-trans
anti / s-cis
UV-DUV pump-probe scheme n1
n1(UV)
n2(DUV)
IC (ISC) Dt
Ionization efficiency
Curve from the dark
state.
→　Ionization threshold
=46790 cm-1
n2 wavenumber / cm-1

5. Assignment of Dark State of p-MMC (1np*, Triplet ?)
(a) Possibility #1
(b) Possibility #2
Yamazaki et al. J. Phys. Chem. Lett. 7, 4001 (2016)
Over all time scale of S1→T1 : ps
1np*
T1(pp*)
S1(pp*) and 1np* are strongly
vibronicaly coupled
T1(pp*) decays with a lifetime of ~20 ns

6. Decay route p-MMC from S1 (trans) to S0 (cis)
GRRM(Global Reaction Route Mapping)
By K. Yamasaki and S. Maeda
Yamazaki et al.
J. Phys. Chem. Lett. 7, 4001 (2016)

7. Nonradiative decay route of methylcinnamate
Double-bond twist in the S1(ππ*) state
S1(ππ*)→ 1nπ* Internal conversion ① ②

8. Nonradiative decay and trans → cis photo-isomerization of o-, m-,p-hydroxy methylcinnamate
o-HMC
m-HMC
p-HMC
Method
○　Experimental
　　　1. IR spectroscopy of cold matrix (Ne at 6K) isolated species
　　　2. Lifetime measurement of S1 by picosecond UV-UV’ pump-probe method
　　　3. Detection of the dark (T1) state by nanosecond UV-Deep UV pump-probe method
○　Theoretical
　　　1. Search for Conical Intersection (CI) by Global Reaction Route Mapping (GRRM)
　　 developed by Ohno and Maeda
　　　2. Determination of the energy of MECI by TD-DFT method

9. Photochemistry of p-, m-, o-hydroxy methylcinnamate (HMC)
Cold(6K) Matrix Isolation IR spectroscopy
p-HMC
m-HMC
o-HMC
Before UV irradiation
Difference spectra after UV irradiation
C=O
Propenyl C=C
Ring C-C
p-HMC
m-HMC
o-HMC
All the structural isomers of HMC proceed trans → cis photo-isomerization

10. S1-S0 Electronic spectra of p-,m-, and o-HMC in supersonic beam
9ps
17 ns
10 ns

11. Energy level diagram and time profiles of S1 and T1 of p-HMC
Decay of the S1 state
Decay of the T1 state
t=27 ns
Ionization threshold
From the dark state
Energy level diagram
n1(UV)
n2(DUV)
IC (ISC) Dt

12. Lifetimes of the vibronic bands of S1 of m-HMC
Nanosecond UV-DUV pump-probe
Picosecond UV-UV’ pump-probe
700 ps
190 ps
350 ps
125 ps
All the decay curves could be fitted by single exponential decay curves

13. Excess Energy Dependence of the S1 lifetime
m-HMC
o-HMC
Double-exponential
Decay
Above Excess = ~1100 cm-1,
non-radiative channel opens
Above Excess = ~500 cm-1,
non-radiative channel opens

14. × m-HMC (and o-HMC) does not have T1 production channel Nanosecond
UV-Deep UV pump-probe
experiment
p-HMC
(0,0) band exc.
T1 state
t = 27 ns
n1(UV)
n2(DUV)
(50000 cm-1)
IC (ISC) Dt ×
< 300 ps
n2= cm-1 exc.
(Eexess = 2100 cm-1)
m-HMC
No production of T1 state
→　No IC (1np*) route
decay

15. Search of the Decay route m-MMC by GRRM method
Structural Change along the C=C double bond
a TD-ωB97XD/6-311G(d,p) w. zero-point energy correction
b SF-TD-BHHLYP/6-311G(d,p) w/o zero-point energy
MECI
1np*/ 1pp* x
1pp*(S1) →1np* IC
route is less probable,
because of the higher
energy of
conical intersection (MECI)
34938
1257 cm-1
1695 cm-1

16. Summary Photochemistry after excitation of the S1(1pp*) state
has been investigated for trans-p-, m-, and o-HMC)
All the species proceed trans→cis isomerization
Cis-photoproduct production channel is different
between p-HMC and m-, o-HMC
p-HMC
S1(1pp*)
→ S2(1np*)
→ (T2) →T1→ S0 (trans or cis)
m-, o-HMC
→ Structural change in S1 surface
→ CI with S0 at 98 degree
→ S0 (trans or cis)
cis
trans

17. Tokyo University of Agriculture and Technology
Special Thanks to
Hiroshima University
Dr. Yasunori Miyazaki,
Mr. Yuuki Onitsuka
Prof. Hiroshi Kohguchi
Dr. Yoshiya Inokuchi,
Tokyo University of Agriculture and Technology
Dr. Nobuyuki Akai,
Institute for Molecular Science
Prof. Masahiro Ehara,
Hokkaido University
Dr. Kaoru Yamazaki
Prof. Satoshi Maeda,