Study of Acyl Group Migration by Femtosecond Transient Absorption Spectroscopy and Computational Chemistry

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• 作者：Elena A. Pritchina ; Nina P. Gritsan ; Gotard T. Burdzinski ; Matthew S. Platz
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：October 25, 2007
• 年：2007
• 卷：111
• 期：42
• 页码：10483 - 10489
• 全文大小：336K
• 年卷期：v.111,no.42(October 25, 2007)
• ISSN：1520-5215

文摘

The primary photophysical and photochemical processes in the photochemistry of 1-acetoxy-2-methoxyanthraquinone (1a) were studied using femtosecond transient absorption spectroscopy. Excitation of 1a at 270nm results in the population of a set of highly excited singlet states. Internal conversion to the lowest singletn* excited state, followed by an intramolecular vibrational energy redistribution (IVR) process, proceedswith a time constant of 150 ± 90 fs. The ¹n* excited state undergoes very fast intersystem crossing (ISC,11 ± 1 ps) to form the lowest triplet * excited state which contains excess vibrational energy. The vibrationalcooling occurs somewhat faster (4 ± 1 ps) than ISC. The primary photochemical process, migration of acetoxygroup, proceeds on the triplet potential energy surface with a time constant of 220 ± 30 ps. The transientabsorption spectra of the lowest singlet and triplet excited states of 1a, as well as the triplet excited state ofthe product, 9-acetoxy-2-methoxy-1,10-anthraquinone (2a), were detected. The assignments of the transientabsorption spectra were supported by time-dependent DFT calculations of the UV-vis spectra of the proposedintermediates. All of the stationary points for acyl group migration on the triplet and ground state singletpotential energy surfaces were localized, and the influence of the acyl group substitution on the rate constantsof the photochemical and thermal processes was analyzed.