標題: | Photoisomerization dynamics of azobenzene in solution with S-1 excitation: A femtosecond fluorescence anisotropy study |
作者: | Chang, CW Lu, YC Wang, TT Diau, EWG 應用化學系 應用化學系分子科學碩博班 Department of Applied Chemistry Institute of Molecular science |
公開日期: | 18-Aug-2004 |
摘要: | Measurements of anisotropy of femtosecond fluorescence after direct excitation of the S-1(npi(*)) state of azobenzene in hexane and ethylene glycol solutions have been carried out to address the controversy about inversion and rotation in the mechanism of photoisomerization. The observed anisotropies in hexane decay to a nonzero asymptotic level with a relaxation period the same as that for slow decay of the corresponding biexponential transient; this effect is attributed to involvement of the out-of-plane CNNC-torsional motion on approach to a twisted conical intersection along the "rotation channel" that depolarizes the original in-plane transition moment. In contrast, when the rotational channel becomes substantially hindered in ethylene glycol, the anisotropies show no discernible decay feature, but the corresponding transients show prominent decays attributed to involvement of in-plane symmetric motions; the latter approach a planar-sloped conical intersection along a "concerted inversion channel" for efficient internal conversion through vibronic coupling. The proposed mechanism is consistent with theoretical calculations and rationalizes both results on quantum yields and ultrafast observations. |
URI: | http://dx.doi.org/10.1021/ja049215p http://hdl.handle.net/11536/26466 |
ISSN: | 0002-7863 |
DOI: | 10.1021/ja049215p |
期刊: | JOURNAL OF THE AMERICAN CHEMICAL SOCIETY |
Volume: | 126 |
Issue: | 32 |
起始頁: | 10109 |
結束頁: | 10118 |
Appears in Collections: | Articles |
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