Synthesis And Application Of Novel Quinoline-based Fluorescent Probe

Small-molecule fluorescent probes have been extensively studied due to their high selectivity,high sensitivity and rapid response time.Quinoline is a typical fluorophore which has a good coordination ability with metal ions.By modifying its structure,it can coordinate with different metal ions and change its fluorescence properties which achieve a response to a particular metal ion.Therefore,it is of great significance to study the influence of different functional groups on the optical properties for further application of quinoline compounds in fluorescent probes.In this thesis,a series of derivatives were designed and synthesized based on quinoline group and the relationship between the structure and the spectral properties of these derivatives was investigated by fluorescence and UV-Vis absorption spectra,and five new fluorescent probes were also developed for detection of Pd²⁺.Firstly,compounds 1-9 were synthesized from quinoline-2-carboxaldehyde,quinoline-8-carboxaldehyde,and 8-hydroxy-2-quinolinecarboxaldehyde by introducing benzimidazole,benzoxazole and benzothiazole groups into 2-position and 8-position of quinoline,respectively.The-NH of benzimidazole derivatives was then replaced to obtain carboxylic acid methyl ester derivatives 10-12 and carboxylic acid derivatives 13-15.The hydroxyl of 8-hydroxyquinoline derivatives was also acetylated to obtain compounds 16-18.Secondly,by comparing the spectral properties of the series of compounds,it was found that the introduction of different substituents and different substituent positions had a great influence on the fluorescence properties of these compounds.The results showed that benzoxazole derivatives had longer fluorescence emission wavelengths than other heterocyclic derivatives.The spectral properties of different substituent positions showed that 8-position substituted heterocyclic compounds had longer fluorescence emission wavelengths than 2-position substituted ones.The emission wavalength of 2-position substituted heterocyclic compounds could be red-shifted by introduction of electron-donating groups such as hydroxyl group and acetoxy group at the 8-position.The 2-position substituted benzimidazole compounds and their derivatives without active hydrogen group at 8-position generally had high fluorescence quantum yield and can emit strong fluorescence.Finally,the fluorescence sensing properties of carboxylic acid methyl ester and carboxylic acid substituted derivatives were investigated by fluorescence sensing tests such as water content,metal ion selectivity and interference,response time,p H effect,complexation ratio,spectral titration and complexation reversibility.The introduction of ester groups and carboxyl groups improved the water solubility of quinoline compounds to enable them to emit strong fluorescence under high water content conditions and the fluorescence of compounds 10,11,13,14 and 15would be significantly quenched with the addition of Pd²⁺.Accordingly,these five compounds were developed as fluorescent probes for the detection of Pd²⁺in aqueous solution,in which compounds 13 and 14 could response to Pd²⁺in pure water and successfully applied to fluorescence imaging in living cells.