Synthesis And Properties Of2,2’–Bisbenzimidazole Derivative Fluorescent Sensors

Anew derivative based fluorescent chemosensor Lwas designed and synthesized.Fluorescent sensor has attracted much attention over the years for its many meritsincluding high specificity and high sensitivity in supramolecular chemistry. Thistechnology has been widely used for the real-time in situ detection of molecularevents both in the environment chemical.2,2’–Bisbenzimidazole can emitfluorescence of big Stokes shift and high fluorescence quantum yield through protonstransfer in molecules. Of all, bifunctional probes, which refer to those based on asingle host that can independently recognize two guest species with distinct spectraresponses by the same or different channels, have already emerged and have graduallybecome a new research focus in the field of fluorescence sensors.In response to these research focus, some novel selective fluorescentchemosensors based on2,2’–Bisbenzimidazole derivative, were developed andcharacterized for the recognition of cations and anions. This thesis mainly containingthe following aspects:Chapter1briefly summaries the application and research progresses of2,2’–Bisbenzimidazole derivative, which as the fluorescent receptor.(Ⅰ) the definitionand design principle of fluorescent sensor;(Ⅱ) the research significance of ionrecognition;(Ⅲ) research progress of selective recognition;(Ⅳ) research progress ofsequential recognition.Chapter2describes synthesis methods involved in this thesis. Compared withconventional methods, the procedures described are easy handing, environmentllycompatible, shorter reaction time (1.5h) and higher yield (96%). The grinding methodis adopted under low temperature including acylation, cyclization and so on.Thestructures have been supported by IR,1H–NMR,13C–NMR, ESI–MS, crystal data,and emission spectral studies. This structurally simple probe displays rapid responseand high selectivity for cyanide over other common anions (F-, Cl-, Br-, I-, AcO-,H--2PO4, HSO4, ClO-4, and SCN-) in aqueous solution. The detection limits for CN-was1×10-9M, 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 cyanide concentrations in aqueous samples.Chapter3revealed2,2’-Bisbenzimidazole derivative (L2) was designed as afluorescent chemosensor for Fe3+. This structurally simple chemosensor displayssignificant fluorescence quenching with increasing concentrations of Fe3+. L2exhibited high selectivity and antidisturbance for Fe3+among environmentallyrelevant metal ions in aqueous media. Moreover, test strips based on L2exhibited agood selectivity to Fe3+. We believe the test strips could act as a convenient andefficient Fe3+test kit.Chapter4reported a series of benzimidazoles fluorescence compounds ofcarboxyl, cyano and other substituents as the basic raw materials for sequentialrecognition of ions based on the displacement approach. Then their fluorescenceemission spectrums in aqueous medium were tested and the influence on fluorescenceproperties of different substituents were studied. Notably, the fluorescenceON–OFF–ON switching is also quite different from other switchings that involved areversible process instead of the forward process used. The benzimidazole derivativesexhibit highly selective and successive recognition of ions in water solution. ThisON–OFF–ON switching process could be repeated at several times with littlefluorescence loss. Furthermore, the detection limit of the sensor L toward Hg2+was1.0×10-9M. Based on properties that sensors reacted with ions and changes of thefluorescence emission intensity by adding ions into sensors with different order, wesuccessfully constructed logic gates. In addition, the chemical inputs of ions in asequential manner generated an output which mimicked the functions of a securitykeypad lock.