Photoinduced Proton-Coupled Electron Transfer of Hydrogen-Bonded p-Nitrophenylphenol鈥揗ethylamine Complex in Solution

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• 作者：Chaehyuk Ko ; Brian H. Solis ; Alexander V. Soudackov ; Sharon Hammes-Schiffer
• 刊名：The Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：January 10, 2013
• 年：2013
• 卷：117
• 期：1
• 页码：316-325
• 全文大小：426K
• 年卷期：v.117,no.1(January 10, 2013)
• ISSN：1520-5207

文摘

Proton-coupled electron transfer can occur through concerted (electron鈥損roton transfer, EPT) or sequential mechanisms, but this distinction becomes less well-defined for photoinduced reactions. These issues have been examined with transient absorption experiments on a hydrogen-bonded complex consisting of p-nitrophenylphenol and t-butylamine. These experiments revealed two spectroscopically distinct states: the higher-energy excited state was interpreted to be a conventional intramolecular charge transfer (ICT) state within the p-nitrophenylphenol, whereas the lower-energy state was interpreted to be an ICT-EPT state, where photoexcitation resulted in both ICT and the shifting of electronic density corresponding to effective proton transfer from the phenol to the amine. In the present work, the singlet excited states of the hydrogen-bonded p-nitrophenylphenol鈥搈ethylamine complex in 1,2-dichloroethane are studied with time-dependent density functional theory and higher-level ab initio methods. The calculations suggest that the 蟺蟺* state, which is the S₁ state at the Franck鈥揅ondon geometry, corresponds to the state denoted ICT-EPT in the experimental analysis, whereas the n蟺* state, which is the S₂ state at this geometry, likely corresponds to the state denoted ICT in the experimental analysis. According to the calculations, the 蟺蟺* state has charge-transfer character, as well as a change in electronic density on the amine, with the minimum-energy structure corresponding to the proton bonded to the nitrogen acceptor, consistent with proton transfer. The n蟺* state has little charge-transfer character, as well as negligible change in electronic density on the amine, with the minimum-energy structure corresponding to the proton bonded to the oxygen donor. The calculations also provide evidence of an avoided crossing between these two states located energetically close to the Franck鈥揅ondon point. These calculations provide the foundation for future nonadiabatic molecular dynamics studies of the relaxation process.