Multifunctional Optical Probes Based On3,5-Dichlorosalicylaldehyde And Its Schiff Base Derivatives

Salicylaldehyde and its Schiff base derivatives, as excellent multiple stimuliresponsive molecules, are good candidates to design new optical probe formultifunctional optical probes. The existing optical probes based on these compoundsare mainly designed by changing the structure of amine in order to detect differentanalytes. In this thesis, we developed new optical probes by changing the substituentgroups of their salicylaldehyde moieties. It should be pointed out that the introduction ofthe ortho-para dichlorine substituents on the phenol group raise the acidity of thephenolic moiety and thus improve properties of the multiple stimuli responses for theprobes. So we have designed an array of multifunctional optical probes for Mg2+, tracewater and pH based on3,5-dichlorosalicylaldehyde and its Schiff base derivatives, andare devoted to the research on their sensing mechanisms and detection properties inorder to develop their applications in materials and biological field. The works in thisthesis mainly contains four aspects as follows:Firstly, based on3,5-dichlorosalicylaldehyde selective chelation towards metalcations, a novel reversible fluorescence “turn-on” Mg2+chemosensor1was designedand developed using a simple commercial3,5-dichlorosalicylaldehyde. According toresearch, the proposed sensor works based on Mg2+-induced formation of the2:11-Mg2+complex generating a chelation-enhanced fluorescence (CHEF) effect andtherefore displaying a fluorescence “turn-on” response. It exhibits high sensitivity andselectivity for the quantitative monitoring of Mg2+with a wide detection range (0-40μM), a low detection limit (3.18×10-7mol/L) and a short response time (<0.5s). It canalso resist the interference from the other co-existing metal ions especially Ca2+.Consequently, this fluorescent sensor can be utilized to real-time monitor Mg2+in realsamples from drinking water. In order to facilitate the applications in portable fieldanalysis for Mg2+, the PMMA thin film doping1molecules was fabricated and used tomonitor Mg2+in drinking water selectively.Secondly, based on a water-triggered hydrolysis reaction of a3,5-dichlori- salicylaldehyde Schiff base, the first water chemodosimeter3was designed andsynthesized. The ortho-para dichlorine substituents on the phenol group promote itshydrolysis reaction in the presence of trace water generating green fluorescent3,5-dichlorosalicylaldehyde and non-fluorescent rhodamine ethanediamine. This processleads to a fluorescence turn-on response and a simultaneous dual channel signalmodulation (both in the fluorescence and absorption spectra). Especially, compound3was found to be an outstanding fluorescence enhancement water sensor in methanolwith an extremely low detection limit of22ppm. Consequently this probe can beutilized to detect trace water in commercial methanol. The quantitative detection of awide range of water content was enhanced in THF and acetonitrile, where thefluorescence peak intensity was nearly proportional to the amount of water added. Thisreveals that this sensor had tremendous potential in quantitative analysis of watercontent in these solvents.Thirdly, based on the hydrolysis reaction of the complex of3,5-dichlori-salicylaldehyde Schiff base (compound4) and Zn(Ⅱ), we first utilized this complexfor the detection of trace amounts of water and a novel fluorescence ratiometric waterchemodosimeter4-Zn(Ⅱ) was developed. In methanol, addition of trace amounts ofwater led to a Zn2+dissociation of the highly blue fluorescent complex4-Zn(Ⅱ)generating free compound4, and followed by a hydrolysis reaction of the ligand4producing the green fluorescent1and the non-fluorescent amine. We were excited tofind that the ratio of these two emission intensities had a significant linear correlationwith the concentration of water content in a range of0-10%. This indicates that it canquantitively detect water over a wide range. In order to further application, the dyestufftest papers absorbing a certain amount of4-Zn(Ⅱ) were prepared to determine thewater content in methanol by naked-eye observation. In THF with low water content,the probe underwent the Zn2+dissociation generating free compound4rather thanthe hydrolysis reaction of newly generated4. While upon the continuous addition oflarge amounts of water, futher dissociation of the complex carried out and thegenerated free ligand4was hydrolyzed. In fluorescence spectra, this process exhibiteda novel fluorescence “ON-OFF-ON” reponse to water content. Compared to waterchemosidometer3, the ratiometric probe4-Zn(Ⅱ) shows comparable detection limitreaching ppm level not only in methanol but also in THF. Therefore,4-Zn(Ⅱ) can beused to determine water content in different grades of commercial THF and distinguish between the freshly purchased HPLC THF and the older wet one.Finally, based on the hydrolysis reaction of3and the respective responses of itshydrolysis products, a new pH probe was designed and developed using compound3.This probe is composed of a non-fluorescent rhodamine derivatives compoud2thatcould stains the acid organelles using ethylene diamine as a linker with another cytosolstaining group compound1. When compound3was added into the aqueous solutionwith different pH values, it underwent the process of the hydrolysis and decomposedinto2and3, and followed by the respective responses of these two hydrolysis productsto H+in different pH ranges. Thus, it exhibited a novel “ON–OFF–ON” typefluorescence and absorption dual-channel signal modulation in aqueous solution towardH+: under neutral conditions, it showed green fluorescence; under acidic conditions, itshowed organge fluorescence. Based on this design of dual fluorophores, probe3possessed a wide detection range of pH value. Furthermore, it exhibited a highselectivity towards H+over other interfering species containing biologically relevantmetal ions. Thereby,3has the potential to be exploited as an efficient candidate formonitoring pH fluctuations in live cells. Interestingly, on account of the respectiveproper pH response ranges under neutral and acidic conditions for3, simultaneous insitu staining and pH monitoring of the cytosol and acidic organelles like lysosomescould be accomplished.