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Science 14 November 2008:
Vol. 322. no. 5904, pp. 1073 - 1077
DOI: 10.1126/science.1160902
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Reports

Spectroscopic Tracking of Structural Evolution in Ultrafast Stilbene Photoisomerization

Satoshi Takeuchi,1 Sanford Ruhman,2 Takao Tsuneda,3 Mahito Chiba,4 Tetsuya Taketsugu,5 Tahei Tahara1*

Understanding a chemical reaction ultimately requires the knowledge of how each atom in the reactants moves during product formation. Such knowledge is seldom complete and is often limited to an oversimplified reaction coordinate that neglects global motions across the molecular framework. To overcome this limit, we recorded transient impulsive Raman spectra during ultrafast photoisomerization of cis-stilbene in solution. The results demonstrate a gradual frequency shift of a low-frequency spectator vibration, reflecting changes in the restoring force along this coordinate throughout the isomerization. A high-level quantum-chemical calculation reproduces this feature and associates it with a continuous structural change leading to the twisted configuration. This combined spectroscopic and computational approach should be amenable to detailed reaction visualization in other photoisomerizing systems as well.

1 Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan.
2 Institute of Chemistry, Hebrew University, Jerusalem 91904, Israel.
3 School of Engineering, University of Tokyo, Tokyo 113-8656, Japan.
4 National Institute of Advanced Industrial Science and Technology, Tsukuba 305-6568, Japan.
5 Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan.

* To whom correspondence should be addressed. E-mail: tahei{at}riken.jp

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Science. ISSN 0036-8075 (print), 1095-9203 (online)