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TDDFT study on the excited-state proton transfer of 8-hydroxyquinoline: Key role of the excited-state hydrogen-bond strengthening

机译:TDDFT研究8-羟基喹啉的激发态质子转移:激发态氢键增强的关键作用

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Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been employed to study the excited-state intramolecular proton transfer (ESIPT) reaction of 8-hydroxyquinoline (8HQ). Infrared spectra of 8HQ in both the ground and the lowest singlet excited states have been calculated, revealing a red-shift of the hydroxyl group (-OH) stretching band in the excited state. Hence, the intramolecular hydrogen bond (O-H center dot center dot center dot N) in 8HQ would be significantly strengthened upon photo-excitation to the S-1 state. As the intramolecular proton-transfer reaction occurs through hydrogen bonding, the ESIPT reaction of 8HQ is effectively facilitated by strengthening of the electronic excited-state hydrogen bond (O-H center dot center dot center dot N). As a result, the intramolecular proton-transfer reaction would occur on an ultrafast timescale with a negligible barrier in the calculated potential energy curve for the ESIPT reaction. Therefore, although the intramolecular proton-transfer reaction is not favorable in the ground state, the ESIPT process is feasible in the excited state. Finally, we have identified that radiationless deactivation via internal conversion (IC) becomes the main dissipative channel for 8HQ by analyzing the energy gaps between the S-1 and S-0 states for the enol and keto forms. (C) 2014 Elsevier B.V. All rights reserved.
机译:密度泛函理论(DFT)和时变密度泛函理论(TDDFT)计算已用于研究8-羟基喹啉(8HQ)的激发态分子内质子转移(ESIPT)反应。计算了基态和最低单重态激发态下8HQ的红外光谱,揭示了激发态下羟基(-OH)拉伸带的红移。因此,光激发至S-1状态时,8HQ中的分子内氢键(O-H中心点中心点中心点N)将显着增强。由于分子内质子转移反应通过氢键发生,因此通过增强电子激发态氢键(O-H中心点中心点中心点N)可以有效地促进8HQ的ESIPT反应。结果,分子内质子转移反应将在超快的时间尺度上发生,而在ESIPT反应的计算出的势能曲线中的势垒可忽略不计。因此,尽管分子内质子转移反应在基态下是不利的,但是ESIPT过程在激发态下是可行的。最后,我们通过分析烯醇和酮形式的S-1和S-0状态之间的能隙,确定了通过内部转换(IC)进行无辐射失活成为8HQ的主要耗散通道。 (C)2014 Elsevier B.V.保留所有权利。

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