咔唑基席夫碱类化合物合成与分子内可交换氢键(ITP)对吸收和荧光光谱的影响

Synthesis of Carbazole Based Schiff Base Compounds and the Effect of Intramolecular Hydrogen Bonding (ITP) on Absorption and Fluorescence

对于分子探针试剂来说,实现可见光波长范围内的激发-发射,是应用于生物活体的前提条件。咔唑是光敏试剂和生物试剂的重要基体,广泛应用于光敏染料和药物合成。基于分子内强烈氢键效应(SHB)能够显著红移分子吸收与荧光波长的策略,在咔唑席夫碱分子内引入可交换质子官能团(ITP),合成了35个新席夫碱化合物,通过1HNMR、13 CNMR、HRMS、IR进行了表征,确认了其结构。对它们在紫外-可见光吸收性质进行了研究,考察了不同取代基的影响,发现基于SHB的扩环效应导致吸收-发射波长红移到可见光区,ITP效应降低了咔唑环能级差导致吸光强度下降,而相应的荧光发射研究结果则表明,SBH的扩环效应使得荧光发射光谱大幅度红移。具有SHB扩环效应的分子,荧光发射强度也大大增加。与单咔唑相比,双咔唑基席夫碱体系中不管桥结构是柔性的还是刚性桥基,咔唑环上引入—OH的分子都实现了可见光区激发→荧光发射调控。

It is very important for molecular probe reagents to achieve excitation-emission within the visible light wavelength range,it is also a prerequisite for their application in living organisms.Carbazole is an important matrix for photosensitive and biological reagents,widely used in the synthesis of photosensitive fuels and drugs.Based on the strong hydrogen bonding effect(SHB)within the molecule,which can significantly redshift the absorption and fluorescence emission wavelengths.An exchangeable proton functional group(ITP)into the carbazole Schiff base molecule,and 35 Schiff base compounds have been synthesized and characterized by 1HNMR,13 CNMR,HRMS,and IR.The effect of different substituents on their UV-visible absorption properties has been studied,it was found that the ring expansion effect based on SHB made the absorption-emission wavelength redshift to the visible region.It was also found that the ITP effect reduced the energy level difference of the carbazole ring,which leading to a decrease in absorbance intensity.Furthermore,the corresponding fluorescence emission results implied that the ring expansion effect caused a significant redshift in the fluorescence emission spectrum.Surprisingly,molecules with SHB effect also exhibited significantly increased fluorescence emission intensity.It should be pointed out that compared with monocarbazole,in the dicarbazole based Schiff base system,regardless of whether the bridge structure was flexible or rigid,the introduction of—OH molecules on the carbazole ring achieved visible light excitation fluorescence emission regulation.