Nonradiative decay dynamics of methyl-4-hydroxycinnamate and its hydrated complex revealed by picosecond pump-probe spectroscopy

作者：Shimada Daiki; Kusaka Ryoji; Inokuchi Yoshiya; Ehara Masahiro^*; Ebata Takayuki

来源：Physical Chemistry Chemical Physics, 2012, 14(25): 8999-9005.

DOI：10.1039/c2cp24056d

The lifetimes of methyl 4-hydroxycinnamate (OMpCA) and its mono-hydrated complex (OMpCA-H2O) in the S-1 state have been measured by picosecond pump-probe spectroscopy in a supersonic beam. For OMpCA, the lifetime of the S-1-S-0 origin is 8-9 ps. On the other hand, the lifetime of the OMpCA-H2O complex at the origin is 930 ps, which is similar to 100 times longer than that of OMpCA. Furthermore, in the complex the S1 lifetime shows rapid decrease at an energy of similar to 200 cm(-1) above the origin and finally becomes as short as 9 ps at similar to 500 cm(-1). Theoretical calculations with a symmetry-adapted cluster-configuration interaction (SAC-CI) method suggest that the observed lifetime behavior of the two species is described by nonradiative decay dynamics involving trans -%26gt; cis isomerization. That is both OMpCA and OMpCA-H2O in the S-1 state decay due to the trans -%26gt; cis isomerization, and the large difference of the lifetimes between them is due to the difference of the isomerization potential energy curve. In OMpCA, the trans -%26gt; cis isomerization occurs smoothly without a barrier on the S-1 surface, while in the OMpCA-H2O complex, there exists a barrier along the isomerization coordinate. The calculated barrier height of OMpCA-H2O is in good agreement with that observed experimentally.

• 出版日期2012