Design And Synthesis Of Optical Chemosensors And Study Of Its Recognition Properties

Fluorescent and colorimetric chemosensors for selectively detecting ions are widely used in many fields. The advantages of fluorescence chemosensors are high selectivity, sensitivity and simplicity. Colorimetric sensors are popular due to their capability to detect analyte by the naked eye without resorting to any expensive instruments. In this thesis, a series of new optical chemosensors were synthesized and investigated for their applications in the detection of heavy metal cations (Cd²⁺, Hg²⁺) and fluoride anion (F-). The details are as follows:1. A fluorescein based chemosensor 1 exhibiting good water solubility and biocompatibility was synthesized and characterized. The selectivity of compound 1 to Cd²⁺ in HEPES buffer solution from a series of cations is evident as its exceptional fluorescence enhancement. The sensitivity of compound 1 to Cd²⁺ was illustrated in living cells, indicating its potential application for Cd²⁺ diagnoses in clinics.2. Rhodamine-based chemosensors with free thiol monomer A, and disulfide linked dimers B and C were designed for Hg²⁺ recognition by virtue of the strong affinity of mercury to sulfur. Spectroscopic results reveal that chemosensor C exhibits real-time response, high sensitivity and selectivity to Hg²⁺ by comparison to other cations, mechanistically ascribed to the transfer from rhodamine spirolactam to thiazoline derived open ring rhodamine via Hg²⁺ induced desulfurization. The utilization of C for monitoring of mercury levels in living cells was thus examined, the imaged Hg²⁺ concentration reaching the safety limit for human beings.3. Two new fluoride colorimetric chemosensor L1 and L2 were designed and synthesized based on coumarin derivatives. A significant color change was observed visually (naked-eye) upon addition of fluoride ions to a solution of compound L1 or L2 in acetonitrile, and other anions such as Cl^-, Br^-, I^-, H₂PO₄^-, NO₃^-, HSO4^-, AcO^-, show no response.4. Photochemical reaction and silanization method were successfully used in modification of cBN surfaces. Further modification of amine-terminated cBN films with fluorescent molecules presents the possibility of practical sensing applications of cBN-based devices.