Molecular Seesaw: How Increased Hydrogen Bonding Can Hinder Excited-State Proton Transfer.
Molecular Seesaw: How Increased Hydrogen Bonding Can Hinder Excited-State Proton Transfer.
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DOI：
10.1021/acs.jpclett.6b01391
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发表时间：
2016-08
期刊：
影响因子：
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通讯作者：
R. Welsch;E. Driscoll;J. Dawlaty;Thomas F. Miller
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文献类型：
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作者：
R. Welsch;E. Driscoll;J. Dawlaty;Thomas F. Miller
本文从理论和实验两方面研究了吲哚衍生物激发态分子内质子转移（ESIPT）相对速率的影响。超快光谱学[j]。化学。A, 2015, 119, 5618-5625]发现虽然1,3-双（2-吡啶基）-4,7-二羟基异吲哚具有两个等效的分子内氢键，但与1,3-双（2-吡啶基）-4-乙氧基-7-羟基异吲哚的单分子内氢键相关的ESIPT速率慢2倍。激发态电子结构计算揭示了一种跷跷板效应，即二醇的两个氢键都比乙氧基醇的单键长，从而解决了这个难题。半经典速率理论恢复了以前无法解释的趋势，并对两个体系中ESIPT的相对H/D动力学同位素效应（KIE）进行了明确的预测。利用超快光谱学对理论KIE预测进行了测试，证实了跷跷板效应。
A previously unexplained effect in the relative rate of excited-state intramolecular proton transfer (ESIPT) in related indole derivatives is investigated using both theory and experiment. Ultrafast spectroscopy [ J. Phys. Chem. A, 2015, 119, 5618-5625 ] found that although the diol 1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole exhibits two equivalent intramolecular hydrogen bonds, the ESIPT rate associated with tautomerization of either hydrogen bond is a factor of 2 slower than that of the single intramolecular hydrogen bond in the ethoxy-ol 1,3-bis(2-pyridylimino)-4-ethoxy-7-hydroxyisoindole. Excited-state electronic structure calculations suggest a resolution to this puzzle by revealing a seesaw effect in which the two hydrogen bonds of the diol are both longer than the single hydrogen bond in the ethoxy-ol. Semiclassical rate theory recovers the previously unexplained trends and leads to clear predictions regarding the relative H/D kinetic isotope effect (KIE) for ESIPT in the two systems. The theoretical KIE predictions are tested using ultrafast spectroscopy, confirming the seesaw effect.