Synthesis And Performance Of A Fluorescent Chemosensor Based On Acylhydrazone Based Supramolecular Gels

Low molecular weight gels（LMWGs）have been widely studied and applied in the field of supramolecular chemistry due to their ability to construct functional soft materials through non-covalent interactions.These soft materials not only retain some of the characteristics of the solution and solid state,but also offer the ability to synergistically tune their properties through a combination of many influencing factors（eg.temperature,type of gelling agent,and solvent）.with their self-assembled structures,three-dimensional networks and large specific surface areas,LMWGs have found a wide range of applications in many fields.Among these LMWGs,fluorescent LMWGs have received increasing attention due to their excellent photophysical properties,especially their aggregation-induced emission behaviour.The above-mentioned advantages give fluorescent LMWGs excellent sensing capabilities with multiple detection pathways（solution state,gel state,and dry gel state）and signal modes（colour change,fluorescence intensity change,and gel state change）.This thesis paper provides a short categorical summary of the research work done in this direction by researchers at home and abroad in recent years.By reading a large amount of literature and the work done by our group in recent years on supramolecular gel fluorescence chemosensors,three supramolecular self-assembled gel chemosensors based on acylhydrazone groups were designed and prepared,and their performance in ion recognition detection was investigated.The discussion in this thesis is developed in the following five aspects:In Chapter 1,introduces the domestic and international research progress and classification of supramolecular gel chemical sensors,analyses and summarizes the previous research ideas,and presents the research ideas and methods of this thesis in conjunction with the existing research work of our group.In Chapter 2,a self-assembled supramolecular gel fluorescence chemosensor based on an acylhydrazone group was designed and prepared by a three-step method for the ultrasensitive alternating detection of Fe³⁺and H₂PO₄^-.The gel factor DN is designed as a conjugated structure in the molecular structure,mainly to facilitate its aggregation-induced emission and to allow a high fluorescence quantum yield.The gel factor DN can form supramolecular gels（ODN）in DMF solvents through intermolecular hydrogen bonding andπ-πstacking,and ODN exhibits intense blue aggregation-induced emission（AIE）.Importantly,the ODN enables ultra-sensitive dual-channel detection of Fe³⁺and H₂PO₄^-by means of an“ON-OFF-ON”pattern of fluorescence intensity.In addition,the supramolecular sensor ODN can be used as a fluorescent smart material with good results.With a limit of detection（LOD）of 4.23×10^-8 M for Fe³⁺,the practical application of ODN shows its potential as a bifunctional fluorescent display material for biosystem monitoring.In Chapter 3,an acylhydrazone supramolecular gel sensor OQN with ion detection of the dual fluorophores quinoline and naphthalene was successfully constructed by introducing two different conventional fluorophores quinoline and naphthalene into the molecular structure.The gel factor QN can form supramolecular gels（OQN）in DMF solvent through intermolecular hydrogen bonding andπ-πstacking.the OQN exhibits intense bright yellow aggregation-induced emission（AIE）.Importantly,the OQN enables ultra-sensitive detection of Fe³⁺and Cu²⁺by means of an“ON-OFF”mode of fluorescence intensity.In addition,the supramolecular sensor OQN can be used as a fluorescence smart display material with a limit of detection（LOD）of up to 1.56×10^-8 M for Fe³⁺and 1.23×10^-8 M for Cu²⁺.In Chapter 4,a three-step method was used to synthesise a gel factor N containing two naphthalene conventional fluorophores in the molecular structure,which can form a supramolecular gel ON in a mixture of DMSO and H₂O through intermolecular hydrogen bonding andπ-πstacking.ON exhibits intense yellowish aggregation-induced emission（AIE）.ON enables ultra-sensitive detection of Fe³⁺through the fluorescence intensity“ON-OFF”mode.In addition,the supramolecular gel fluorescence chemosensor ON can be used as a fluorescent smart safety display material with good results,and the limit of detection（LOD）for Fe³⁺is up to 1.30×10^-7 M.This shows the potential of ON as a functional fluorescent display material for monitoring biological systems.In Chapter 5,a summary comparative analysis of the three designed and prepared supramolecular gel fluorescence chemosensors is presented and a brief evaluation of the expected effect of recognition detection is made.The gel factors of all three systems in this thesis were synthesised using a three-step method.The gel factors of all three systems were based on acylhydrazone bonds in their molecular structure,and their main purpose was to increase the self-assembly weak interactions and improve the structural properties of the gels.On this basis the design idea of introducing conjugated,dual fluorophores into the molecular structure was used to investigate the effect of the presence or absence of fluorophores and the type of fluorophore on the fluorescence properties of the gels.The detection limits of all three supramolecular gel fluorescence chemosensors were relatively low in terms of recognition detection,indicating that the sensitivity of the sensors achieved the expected results.