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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Photoinduced Generation of the pi-Conjugated Zwitterionic State in the ESIPT Fluorophore of 2,4-Bisimidazolylphenol
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Photoinduced Generation of the pi-Conjugated Zwitterionic State in the ESIPT Fluorophore of 2,4-Bisimidazolylphenol

机译：在2,4-bisimidazolyl苯酚的Esipt荧光团中光诱导的pi缀合的两性离子状态产生

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摘要

We demonstrate that 2,4-bis(4,5-diphenyl-1H-imidazol-2-yl)phenol (2,4-bImP) undergoes photoinduced conversion into the so-called "pi-conjugated zwitterion" after causing an excited-state intramolecular proton transfer (ESIPT) reaction. The powder sample of 2,4-bImP exhibits largely Stokes-shifted fluorescence characteristics to ESIPT fluorophores. On the other hand, its originally colorless solutions become colored when exposed to UV light for several minutes, whose color depends on the type of solvent. In particular, the CHCl3 solution rapidly turns dark green with the absorption maximum around 700 nm, and the colored solution is nearly restored to original by alternating addition of acid and base. To explain such drastic and reversible color changes, we hypothesized that the occurrence of ESIPT (i.e., deprotonation of the phenol and protonation of the imidazolyl group at its 2-position) triggered the charge-separated structure between the negatively charged phenolate and the positively charged imidazoliumyl group at its 4-position, which allowed resonance with the neutral p-quinoid structure. The formation of this pi-conjugated zwitterion was strongly supported by the results of and H-1 NMR and Raman measurements.
机译：我们证明，2,4-双（4,5-二苯基-1H-咪唑-2-基）苯酚（2,4-bImP）在引发激发态分子内质子转移（ESIPT）反应后，经历光诱导转化为所谓的“π共轭两性离子”。2,4-bImP粉末样品的荧光特性在很大程度上由斯托克斯位移转变为ESIPT荧光团。另一方面，其原本无色的溶液在紫外线照射几分钟后会变色，其颜色取决于溶剂的类型。特别是，CHCl3溶液迅速变为深绿色，最大吸收波长约为700 nm，通过交替添加酸和碱，有色溶液几乎恢复到原始状态。为了解释这种剧烈且可逆的颜色变化，我们假设ESIPT的出现（即苯酚的脱质子化和咪唑基在其2位上的质子化）触发了带负电荷的苯酚基和带正电荷的咪唑基在其4位上的电荷分离结构，它允许与中性对喹啉结构共振。这种π共轭两性离子的形成得到了核磁共振和拉曼光谱测量结果的有力支持。

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