Synthesis And Recognition Properties Of Fluorescent Chemosensors Based On Thiosemicarbazone And Schiff Base

Ion recognition is one of the most important parts of supramolecular chemistry,the development of sensitive and selective chemosensors for important ions are ofintense current interest because these ions play important roles in our living systemand environment, but it is still a large challenge to realize selective recognition forsome ions, chemosensors that discriminates closely related ions is an ideal goal.Selective recognition for ions based on ion-participating reaction and specialcoordination with heteroatoms seems very meaningful. Starting on these issues,recognition for cations and anions based on thiosemicarbazone and Schiff basereceptors are invested by UV-vis spectrum and fluorescence spectrum. There are fourchapters in this thesis:Chapter one: Principle and research progress of fluorescent chemosensorsfor ions recognitionIn this chapter the research progress of fluorescent chemosensors in terms ofrecognition principle for ion recognition was briefly reviewed based on intramolecularcharge transfer (ICT), photoinduced electron transfer (PET), fluorescence resonanceenergy transfer (FRET), excited-state intramolecular proton transfer (ESIPT),monomer-excimer (EM) and chelation-enhanced fluorescence (CHEF), act.Chapter two: Synthesis and Hg2+recognition properties ofthiosemicarbazone derivantA simple Hg2+-selective chemodosimetric system based on thiosemicarbazonewas investigated. The transformation of thiosemicarbazone into semicarbazoneselectively exerted by Hg2+ions and the dimerization of semicarbazone resulted in apronounced OFF-ON-type fluorescent signaling behavior. The coexistent metal ions,such as Fe3+, Ca2+, Cu2+, Co2+, Ni2+, Cd2+, Pb2+, Zn2+, Cr3+, Mg2+, Na+, K+and Fe2+,had no obvious interference with the detection of Hg2+. In addition, S12-Hg2+plays ahigh sensitivity for basic anions to form an “OFF–ON–OFF” type signaling behavior,with the Hg2+-induced emission spectra can be quenched. Moreover, test strips basedon S12exhibited a good selectivity to Hg2+. We believe the test strips could act as aconvenient and efficient Hg2+test kit. Chapter three: Synthesis and cation recognition properties of a novelSchiff base based on2-hydroxynaphthaldehydeA simple cation sensor bearing naphthol OH and imine group was designed andsynthesized, which showed fluorescence turn-on response for Zn2+based onChelation-Enhanced Fluorescence (CHEF) principle. Meanwhile the rapidenhancement of fluorescence emission provide naked eyes detection for Zn2+.Moreover, the sensing of Zn2+was found to be reversible, with the Zn2+-inducedemission spectra being quenched upon addition of EDTA. Even more important, thissensor provides a novel approach for selectively recognizing one of the mostimportant trace elements by emission spectrum.Chapter four: Synthesis and cyanide recognition properties of a simpleSchiff base based on2-hydroxynaphthaldehydeA colorimetric and fluorescent cyanide probe bearing naphthol and imine grouphas been designed and synthesized. This structurally simple probe displays rapidresponse and high selectivity for cyanide over other common anions (F-, Cl-, Br-, I-,AcO-, H2PO4-, HSO4-, ClO4-, and SCN-) in aqueous solution based on theIntramolecular Charge Transfer (ICT) principle. The sensing of cyanide wasperformed via the nucleophilic attack of cyanide anion to imine groups of the probewith a1:2binding stoichiometry, and the fluorescence enhancement of the sensor ismainly due to the ICT process improvement. The detection limits for CN-was4.0×10-7M, which is far lower than the WHO guideline of1.9×10-6M. Thus, thepresent probe should be applicable as a practical system for the monitoring of cyanideconcentrations in aqueous samples.