Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamilnadu, India.
J Fluoresc. 2011 Mar;21(2):595-606. doi: 10.1007/s10895-010-0747-5. Epub 2010 Nov 3.
A group of novel 2-aryl imidazole derivatives were synthesized and characterized by NMR spectra, X-ray, mass and CHN analysis. An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazoles (dmip and dmtip) have been studied using emission spectroscopy and it was detected that the two distinct ground state rotamers of I and II are responsible for the normal and the tautomer emission respectively. In hydrocarbon solvent, the tautomer emission predominates over the normal emission for both dmip and dmtip. This reveal that rotamer II is responsible for the tautomer emission and it is stabler than rotamer I which causes the normal emission. In alcoholic solvent like ethanol, a dramatic enhancement of normal emission is observed which was due to increased solvation, the more polar rotamer I become stabler than rotamer II. In dioxane-water mixtures it is observed that the addition of water inhibits the ESIPT process due to the formation of the intermolecular hydrogen bonding involving water. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the imidazole derivatives were performed and discussed. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state.
一组新型 2-芳基咪唑衍生物被合成并通过 NMR 谱、X 射线、质谱和 CHN 分析进行了表征。通过发射光谱研究了羟基咪唑（dmip 和 dmtip）中的激发态分子内质子转移（ESIPT）过程，发现 I 和 II 两种不同的基态构象异构体分别负责正常和互变异构体发射。在烃溶剂中，dmip 和 dmtip 的互变异构体发射均优先于正常发射。这表明构象异构体 II 负责互变异构体发射，它比导致正常发射的构象异构体 I 更稳定。在乙醇等醇类溶剂中，观察到正常发射显著增强，这是由于溶剂化增加，极性更强的构象异构体 I 变得比构象异构体 II 更稳定。在二氧六环-水混合物中，观察到由于涉及水的分子间氢键的形成，水的添加抑制了 ESIPT 过程。对咪唑衍生物的基态和激发态的构象异构体的能量、偶极矩、电荷分布进行了 DFT 计算和讨论。PES 计算表明，在激发态下，两种构象异构体之间的转换能垒比基态高得多。
