A set of π-expanded imidazole derivatives employing excited state intramolecular proton transfer (ESIPT) was designed and synthesized. The relationship between the structure and photophysical properties were thoroughly elucidated by comparing with the analogue blocked with ESIPT functionality. The compound possessing an acidic NH function as part of an intramolecular hydrogen bond system has much higher fluorescence quantum yield and Stokes shift and the π-expansion strongly influences the optical properties. The occurrence of ESIPT for imidazole tosylamide derivatives were less affected by the hydrogen-bonding ability of the solvents compared to the unprotected amine. The low pKa values for the monocation ⇌ neutral equilibrium indicate the presence of intramolecular hydrogen bonding between the amino proton and tertiary nitrogen atom.
设计并合成了一组利用激发态分子内质子转移(ESI
PT)的π-扩展
咪唑衍
生物。通过与阻断了 ESI
PT 功能的类似物进行比较,深入阐明了其结构与光物理特性之间的关系。作为分子内氢键系统的一部分,具有酸性 NH 功能的化合物具有更高的荧光量子产率和斯托克斯位移,而且 π 的扩展对其光学性质有很大影响。与未受保护的胺相比,
咪唑对
甲苯磺酰胺衍
生物发生 ESI
PT 的情况受溶剂氢键能力的影响较小。单定位⇌中性平衡的 pKa 值较低,表明
氨基质子和叔氮原子之间存在分子内氢键。