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

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

Investigation of the dark sate Possibility 2 : S1(ππ*)→ 1nπ* Internal conversion Picosecond UV+ UV’ pump-probe pMMC Miyazaki et al., J. Chem. Chem., 141 244313 (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

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

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 : 100 -200 ps 1np* T1(pp*) S1(pp*) and 1np* are strongly vibronicaly coupled T1(pp*) decays with a lifetime of ~20 ns

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)

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

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

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

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

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

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

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

× 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= 33480 cm-1 exc. (Eexess = 2100 cm-1) m-HMC No production of T1 state →　No IC (1np*) route decay

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

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

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,