Synthesis And Properties Of Polyhydroxybenzoylhydrazone Fluorescent Compounds

Acylhydrazone is a kind of special Schiff base with good stability which is synthesized by a condensation reaction between hydrazide and active carbonyl compound.Acylhydrazones are widely used in the synthesis of fluorescent probes,antibacterial drugs and antitumor drugs because of their excellent metal ion coordination ability and biological activity.Besides,introducing hydroxyl to acylhydrazone structure can change some photophysical properties of acylhydrazone compounds.When the hydroxyl group on the benzene ring is on ortho position,it will cause an excited-state intramolecular proton transfer(ESIPT)process.At present,the researches of polyhydroxybenzoylhydrazone fluorescence compounds mainly focus on the coordination ability between molecules and metal ions,while the researches on the photophysical properties and the molecular interaction of these compounds are relatively rare.In this paper,a series of hydroxybenzaldehyde benzoylhydrazone compounds whose positions of phenolic hydroxyl are different were designed and synthesized firstly,and then their solid and liquid photophysical properties were tested.The results show that the introduction of o-hydroxy group can make hydroxybenzaldehyde benzoylhydrazone compounds have larger Stokes shift and higher fluorescence quantum efficiency,and 2-hydroxybenzaldehyde-2-hydroxybenzoylhydrazone has the highest fluorescence quantum efficiency(28.31%).Based on these research results,1,1,2,2-tetra(3-aldehyde-4-hydroxyphenyl)ethylene which has o-hydroxy group was designed and synthesized,and then condensed with o-hydroxybenzoylhydrazide,m-hydroxybenzoylhydrazide and p-hydroxybenzoylhydrazine respectively to obtain three kinds of polyhydroxybenzoylhydrazone tetraphenylethylene fluorescent compounds whose positions of phenol hydroxyl were different.Then their solid and liquid photophysical properties were tested.The results show that all the three compounds have aggregation-induced emission(AIE)property and excited-state intramolecular proton transfer(ESIPT)property.Besides,adding bad solvent into good solution of1,1,2,2-tetra(3-(2-hydroxybenzoylhydrazone)-4-hydroxyphenyl)ethylene molecule can obtain organogel rapidly,and during this gelation process,the changes of optical properties and rheological mechanical properties are synchronous,so that we can realize in-situ visual monitoring of this gelation process by detecting the change of fluorescence emission spectrum of organogel.By analyzing the results of XRD,IR,SEM and ~1H-NMR,we believe that this low molecular organogel mainly integrates a three-dimensional porous network structure through intermolecular hydrogen bonding.In this paper,2-hydroxybenzaldehyde-2-hydroxybenzoylhydrazone which has good photophysical properties is combined with tetraphenylethylene structure to obtain a compound which has both AIE and ESIPT properties.This work provides a new way to change the optical properties of tetraphenylethylene fluorescent compounds.Besides,based on the formation mechanism of low molecular organogel,we tried to add bad solvent into the good solution of organic molecule to obtain low molecular organogel.Compared with the traditional heating-cooling method,this method is more convenient and this gelation process can be monitored synchronously through the change of fluorescence emission spectrum,avoiding the damage to the organogel which cannot be avoided by the traditional test method.This method provides a new idea and method for the preparation of the organogel and the monitor of the gelation process.