Temperature Effect on Dual Fluorescence of 2-(2′-Hydroxyphenyl)benzimidazole and Its Nitrogen Substituted Analogues
Temperature Effect on Dual Fluorescence of 2-(2′-Hydroxyphenyl)benzimidazole and Its Nitrogen Substituted Analogues
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DOI：
10.1021/jp405804c
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发表时间：
2013-11-14
影响因子：
3.3
通讯作者：
Krishnamoorthy, Govindarajan
中科院分区：
文献类型：
--
作者：
Chipem, Francis A. S.;Krishnamoorthy, Govindarajan
在不同极性和溶剂中研究了温度对 2-(2'-羟基苯基)苯并咪唑 (HPBI) 及其氮取代类似物 2-(2'-羟基苯基)-3H-咪唑并[4,S-b]吡啶 (HPIP-b) 和 2-(2'-羟基苯基)-1H-咪唑[4,S-c]吡啶 (HPIP-c) 双荧光的影响。氢键结合能力。实验研究采用了吸收、稳态和时间分辨发射光谱技术。进行密度泛函理论计算以确定构象异构体的相对数量。计算预测，随着温度的升高，反式烯醇的数量增加，而顺式烯醇的数量减少。在所有温度下，顺式烯醇与反式烯醇的总体比率按 HPIP-c < HPIP-b < HPBI 的顺序增加。除甲醇和乙二醇中的HPBI外，两种发射的荧光都随着温度的升高而减弱，并且在互变异构体带中比在正常带中更明显。使用阿伦尼乌斯方程和范特霍夫方程分析数据。荧光随温度的变化受 (i) 构象异构体相对数量的变化和 (ii) 激发态非辐射衰变的增加控制。正常发射的非辐射衰变的增加与温度升高时反式烯醇相对数量的增加相竞争。
The effects of temperature on the dual fluorescence of 2-(2'-hydroxyphenyl)benzimidazole (HPBI) and its nitrogen substituted analogues, viz., 2-(2'-hydroxyphenyl)-3H-imidazo[4,S-b]pyridine (HPIP-b) and 2-(2'-hydroxyphenyl)-1H-imidazo[4,S-c]pyridine (HPIP-c), were investigated in solvents of different polarity and hydrogen bonding capability. Absorption, steady-state, and time-resolved emission spectroscopic techniques were employed for the experimental study. Density functional theoretical calculations were performed to find the relative population of the conformers. The calculations predict that, with increase in temperature, the population of trans-enol increases, while that of cis-enol decreases. At all temperatures, the population ratio of cis-enol to trans-enol increases in the order HPIP-c < HPIP-b < HPBI. Except for HPBI in methanol and ethylene glycol, the fluorescence of both emissions decreases with an increase in temperature and is more pronounced in the tautomer band than in the normal band. The data are analyzed using the Arrhenius and van't Hoff equations. The change in the fluorescence with temperature is governed by (i) the change in the relative population of conformers and (ii) the increase in non-radiative decay from the excited states. The increase in non-radiative decay from the normal emission competes with the increase in the relative population of trans-enol with a rise in temperature.