TD-DFT Study of the Excited-State Potential Energy Surfaces of 2-(2′-Hydroxyphenyl)benzimidazole and its Amino Derivatives

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• 作者：Hui-Hsu Gavin Tsai ; Hui-Lun Sara Sun ; Chun-Jui Tan
• 刊名：Journal of Physical Chemistry A
• 出版年：2010
• 出版时间：April 1, 2010
• 年：2010
• 卷：114
• 期：12
• 页码：4065-4079
• 全文大小：858K
• 年卷期：v.114,no.12(April 1, 2010)
• ISSN：1520-5215

文摘

In this study, we used TD-PBE0 calculations to investigate the first singlet excited state (S₁) behavior of 2-(2′-hydroxyphenyl)benzimidazole (HBI) and its amino derivatives. We employed the potential energy surfaces (PESs) at the S₁ state covering the normal syn, tautomeric (S₁−T_syn), and intramolecular charge-transfer (S₁−T_ICT) states in ethanol and cyclohexane to investigate the reaction mechanisms, including excited-state intramolecular proton transfer (ESIPT) and intramolecular charge-transfer (ICT) processes. Two new S₁−T_ICT states, stable in ethanol and cyclohexane, were found for HBI and its amino derivatives; they are twisted and pyramidalized. The flat PES of the ICT process makes the S₁−T_ICT states accessible. The S₁−T_ICT state is effective for radiationless relaxation, which is responsible for quenching the fluorescence of the S₁−T_syn state. In contrast to the situation encountered conventionally, the S₁−T_ICT state does not possess a critically larger dipole moment than its precursor, S₁−T_syn state; hence, it is not particularly stable in polar solvents. On the basis of the detailed PESs, we rationalize various experimental observations complementing previous studies and provide insight to understand the excited-state reaction mechanisms of HBI and its amino derivatives.