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噁唑体系激发态质子转移和失活的理论研究
谢斌斌,李春香,崔刚龙,方遒
作者单位E-mail
谢斌斌 北京师范大学化学学院, 理论与计算光化学教育部重点实验室, 北京 100875  
李春香 北京师范大学化学学院, 理论与计算光化学教育部重点实验室, 北京 100875  
崔刚龙 北京师范大学化学学院, 理论与计算光化学教育部重点实验室, 北京 100875 ganglong.cui@bnu.edu.cn 
方遒 北京师范大学化学学院, 理论与计算光化学教育部重点实验室, 北京 100875 fangqiu917@bnu.edu.cn 
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DOI:10.1063/1674-0068/29/cjcp1512242
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基金项目:
Excited-State Proton Transfer and Decay in Hydrogen-Bonded Oxazole System:MS-CASPT2//CASSCF Study
Bin-bin Xie,Chun-xiang Li,Gang-long Cui,Qiu Fang
Abstract:
Herein we have employed high-level multi-reference CASSCF and MS-CASPT2 electronic structure methods to systematically study the photochemical mechanism of intramolecularly hydrogen-bonded 2-(2'-hydroxyphenyl)-4-methyloxazole. At the CASSCF level, we have optimized minima, conical intersections, minimum-energy reaction paths relevant to the excited-state intramolecular proton transfer (ESIPT), rotation, photoisomerization, and the excited-state deactivation pathways. The energies of all structures and paths are refined by the MS-CASPT2 method. On the basis of the present results, we found that the ESIPT process in a conformer with the OH…N hydrogen bond is essentially barrierless process; whereas, the ESIPT process is inhibited in the other conformer with the OH…O hydrogen bond. The central single-bond rotation of the S1 enol species is energetically unfavorable due to a large barrier. In addition, the excited-state deactivation of the S1 keto species, as a result of the ultrafast ESIPT, is very efficient because of the existence of two easily-approached keto S1/S0 conical intersections. In stark contrast to the S1 keto species, the decay of the S1 enol species is almostly blocked. The present theoretical study contributes valuable knowledge to the understanding of photochemistry of similar intramolecularly hydrogen-bonded molecular and biological systems.
Key words:  Excited state proton transfer  Photoisomerization  Conical intersection  Ab initio  Photochemistry