1. Nonradiative Decay Dynamics of Methyl-4-hydroxycinnamate and its Monohydrated Complex revealed by Picosecond Pump-Probe Spectroscopy T. Ebata 1, D. Shimada 1, R. Kusaka 1, Y. Inokuchi 1, H. Ehara 2 1 Department of Chemistry, Hiroshima University, 2 Institute for Molecular Science

2. Trans→cis isomerization of photo-excited p-Coumaric acid Brudler et al. Nature Structural Biology (2001) PYP In Halorhodospira halophila (exhibits negative phototaxis) Methyl-4-hydroxycinnamate (OMpCA)

3. Previous study in the gas phase OMpCA OMpCA-H 2 O Smolarek et al. Phys.Chem.Chem.Phys.2011,13,4393-4399 ・ S 1 -S 0 electronic spectra of OMpCA and its 1:1 hydrated complex in a supersonic beam The lifetime of S 1 OMpCA ： 1.0-1.8ps OMpCA-H 2 O : longer Necessity of direct measurement ● time profile ● energy dependence A large difference of nonradiative process 2.7 cm -1 0.2 cm -1

4. Experimental setup Energy and time resolution are 5 cm -1 and 12 ps, respectively. 1 2 170 ℃ Ne (2.5 atm) Channeltron S0S0 S1S1 IP 0 1 2 tt Pump-probe setup Nd 3+ YAG laser Picosecond IR- UV pump-probe system

5. Conformers of OMpCA anti s-trans syn s-cis syn s-trans anti s-cis

6. R2PI spectra of OMpCA and OMpCA-H 2 O s-trans s-cis picosecond nanosecond

7. S 1 lifetime of bare OMpCA S0S0 S1S1 IP 0 1 2 tt

8. ① ② ③ Region.1Region.3Region.2 The lifetime of the S 1 of OMpCA-H 2 O ①②③ monomer τ=8ps τ 1 =40ps τ 2 =220ps τ=930psτ=8ps 100 times decrease 100 times increase

9. Region.1Region.3Region.2 The lifetime of the S 1 of OMpCA-H 2 O s-transs-cis s-trans (0,0) s-cis (0,0)

10. Mechanism of nonradiative process trans(180˚)cis(0˚) Mechanism 1 (trans→cis isomerization) SAC-CI/D95(d)+Diffuse (by M. Ehara, IMS) Mechanism 2 (IC : S 1 →n  *)) Gromov et al. J. P. C. A 2005, 109, 4623  * H-bonding to the phenolic OH inhibits the trans → cis isomerization

11. Effect of H-bonding strength on the isomerization s-trans s-cis picosecond nanosecond

12. The lifetime of the S 1 of OMpCA-NH 3 ②③ τ=6000ps τ 1 =30ps τ 2 =460ps τ=15ps ① ④ ① ④ ③ ② τ 1 =50ps τ 2 =1000ps (0,0)(0,0)+320cm -1 (0,0)+550cm -1 (0,0)+1000cm -1

13. The lifetime of the S 1 of OMpCA-NH 3

14. Summary The S 1 lifetimes of OMpCA and its H-bonded complexes have been investigated OMpCA8 ps (origin) OMpCA-H 2 O930 ps (origin)8 ps (0,0 + 600 cm -1 ) OMpCA-NH 3 6000 ps (origin)14 ps (0,0 + 1060 cm - 1 ) In OMpCA-H 2 O The lifetime sharply decreases with excess energy(0-600 cm -1 ) Threshold at 400 cm -1 for s-trans, and 530 cm -1 for s-cis Calculation (SAC-CI calculation) ・ The nonradiative process controlling the S 1 lifetime is not the  *→ n  * internal conversion but the trans→cis isomerization ・ OMpCA Trans→cis isomerization occurs without the barrier ・ OMpCA-H 2 O A barrier (~200 cm -1 ) exists at dihedral angle=165˚ H-bonding to the phenolic OH greatly inhibits the nonradiative process

15. Problems to be solved and future works ・ Origin of trans → cis barrier in the H-bonded OMpCA complex Why the barrier exist in the complex but not in the bare form? ・ Possibility of other nonradiative processes Theory ・ Detailed analysis by SAC-CI calculation including full optimized calculation of each excited state for monomer and the complex Experiment ・ Detailed spectroscopic study on OMpCA-NH 3 ・ Time-resolved photoelectron spectroscopy to determine the nonradiative route Problems Future works

16. Many thanks to my group Daiki Shimada

17. Isomerization of OMpCA-H 2 O ① ② ③ Dihedral angle 180° S 1 (s-trans) S 1 (s-cis) 530cm -1 400cm -1 s-trans s-cis Ion intensity H-bonding to the phenolic OH inhibits the trans to cis isomerization

18. Trans→cis isomerization of photo-excited p-Coumaric acid Brudler et al. Nature Structural Biology (2001) Martial Boggio-Pasqua, et al. J. Am. Chem. Soc.,131, (2009) Theoretical calculations predict importances ● SB as well as DB isomerization ● Hydrogen-bonding Cys69 Tyr42 Glu46 pCA PYP In Halorhodospira halophila (bacteria) Gromov et al., J. Phys. Chem. A, 115 (2011)

19. The lifetime of the S 1 of OMpCA-NH 3

20. IR-dip spectra