Time-Resolved and Mechanistic Study of the Photochemical Uncaging Reaction of the o-Hydroxycinnamic Caged Compound

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• 作者：Youqing Yu ; Lidan Wu ; Xiaoran Zou ; Xiaojuan Dai ; Kunhui Liu ; Hongmei Su
• 刊名：The Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：August 22, 2013
• 年：2013
• 卷：117
• 期：33
• 页码：7767-7775
• 全文大小：467K
• 年卷期：v.117,no.33(August 22, 2013)
• ISSN：1520-5215

文摘

The o-hydroxycinnamic derivatives represent efficient caged compounds that can realize quantification of delivery upon uncaging, but there has been lack of time-resolved and mechanistic studies. We used time-resolved infrared (TRIR) spectroscopy to investigate the photochemical uncaging dynamics of the prototype o-hydroxycinnamic compound, (E)-3-(2-hydroxyphenyl)-acrylic acid ethyl ester (HAAEE), leading to coumarin and ethanol upon uncaging. Taking advantage of the specific vibrational marker bands and the IR discerning capability, we have identified and distinguished two key intermediate species, the cis-isomers of HAAEE and the tetrahedral intermediate, in the transient infrared spectra, thus providing clear spectral evidence to support the intramolecular nucleophilic addition mechanism following the trans鈥揷is photoisomerization. Moreover, the product yields of coumarin upon uncaging were observed to be greatly affected by the solvent polarity, suppressed in CH₂Cl₂ but enhanced in D₂O/CH₃CN with the increasing volume ratio of D₂O. The highly solvent-dependent behavior indicates E1 elimination of the tetrahedral intermediate to give rise to the final uncaging product coumarin. The photorelease rate of coumarin was directly characterized from TRIR (3.6 脳 10⁶ s^鈥?), revealing the promising application of such o-hydroxycinnamic compound in producing fast alcohol jumps. The TRIR results provide the first time-resolved detection and thus offer direct dynamical information about this photochemical uncaging reaction.