Reaction-based Chemosensors And Photochromic Bisthienylethene Materials With Ions Recognition Ability

As an active area in supramolecular chemistry, the development of highly sensitive and selective chemosensors, especially corresponding immobilized sensing materials has received increasing attention because of their wide applications in the fields of environment science, industrial manufacturing and biological medicine. In the photoisomerization process of photochromic compounds, both photochemical and photophysical properties will be changed. Photochromic compounds are considered as the most promising materials applied to the fields of molecular switches and optical information storage due to their excellent photochemical and photophysical properties. In recent years, the surge of interest has been aroused by the photochromism integrated with the concept of guest recongnition in supramolecular chemistry.In this thesis, several fluorescent chemosensors were synthesized and devoted to detect Hg2+ and CH3Hg+ with high selectivity and sensitivity. The novel mulfunctional mesoporous silica and membrane materials grafted with chemosensors were prepared for simultaneous detection and adsorption of Hg2+ in aqueous solution. These works inspire researches on the quantitive detection of analysts by chemosensors and the industrialization of chemical sensing materials. In addition, a serial of bisthienylethene compounds featuring unsymmetrical structures were designed and synthezied. These photochromic compounds can serve as chemosensors to detect ions, and their photochromic properties are modulated by ions. Based on photochromism and fluorescence output signals, a smart logic circuit is proposed to carry out complicated logic operation and a molecular keypad lock depending on the input sequence is successfully constructed to protect information at molecular scale. The main contents and results are generalized as following:In Chapter 1, the major sensing principles of the fluorescent chemosensor and the concept of the photochromism are simply introduced. The latest progresses of reaction-based fluorescent chemosensors sensing metal ions and photochromic bisthienylethene materials with ions recognition ability are reviewed.In Chapter 2, two novel chemodosimeters (BTA1 and BTA2) which own a 2,1,3-benzothiadiazole unit as the fluorophore coupling to thiourea recognition moiety were designed and synthesized, and their fluorescent behaviors toward various metal ions were investigated. Chemodosimeter BTA1 shows excellent optical properties and exclusively distinguishes Hg2+ and CH3Hg+ from other metal ions in aqueous solutions. Though the response of chemodosimeter BTA2 to Hg2+ and CH3Hg+ is slower than BTA1, fortunately, it will still serve as a promising fluorescent sensor for Hg2+ and CH3Hg+ with high selectivity. Evidences for the Hg2+ or CH3Hg+-promoted desulfurization mechanism are provided by absorption and fluorescence titration spectra and especially 1H NMR titration as well as HRMS experiments.In Chapter 3, a novel organic-inorganic silica material (MCM-3T), prepared by covalently immobilization of the 2,1,3-benzothiadiazole-based chemodosimeter and thiol group to the mesoporous silica material (MCM-48 type), was characterized by several spectroscopic methods. The MCM-3T shows excellent optical properties with a detection limit of ca.8.O×10-6 M towards Hg2+ under optimized condition and exclusively distinguishes Hg2+ from other metal ions in aqueous solution. The MCM-3T can detect Hg2+ in a large pH range from 5.0 to 11.0, indicating its convenience for practical application. The MCM-3T is also an outstanding adsorbent for the removal of Hg2+ from aqueous solution. The adsorption process of Hg2+ on the MCM-3T is well described by Freundlich isotherm equation and the equilibrium adsorption capacity is 234.88 mg·g-1. Furthermore, a new multifunctional silica membrane was synthesized on an alumina ceramic tube and characterized by SEM. The color and emission color of membrane changed obviously and 90.7% of Hg2+ relative to the initial feed was removed after aqueous Hg2+ solution permeated through the membrane. The simple synthetic strategy, economical starting materials as well as the considerable signal changes exhibit a promising application of the MCM-3T and multifunctional silica membrane for simultaneous detection and separation of Hg2+ in the environmental and industrial fields.In Chapter 4, two new structurally unsymmetrical bisthienylethene derivatives (PI and P2) were designed and synthesized. Compound P1 possesses the gated photochromic reactivity. Compound P1 does not exhibit any photochromic property in organic solution (e.g. acetonitrile) upon alternative irradiation with ultraviolet and visible light. But Cu2+ and water can independently trigger the reversible photochromic reaction of compound P1. Under alternative illumination with ultraviolet and visible light, P2 exhibits a typical photochromic response of bisthienylethene derivatives in CH3CN solution. The photochromic and fluorescent properties of compound P2 and its complex with Cu2+ are tailored by Cu2+ and CN coordinations. Furthermore, compound P2 is used to develop a complicated logic circuit for a molecular traffic signal with three inputs and three outputs. A molecular keypad lock with memory storage function is constructed to visualize these sequence-dependent phenomena. This present work provides deeper insights for the future design of functional photochromic compounds featuring special structures. In Chapter 5, two new chemosensors (P5 and P6) based on photochromic dithienylcyclopentene were designed and synthesized, and their spectral behaviors toward various metal ions and anions were investigated in detail. Compounds show excellent optical properties and distinguish Hg2+ and F- in CH3CN. Job's plot reveals that the presence of Hg2+ induces the formation of a 1:1 complex between P5 or P6 and Hg2+. From the spectral responses and 1H NMR analysis, the deprotonation of the thioamide protons is proposed to explain the sensing mechanism for P5 and P6 toward F-. It is found that P5 and P6 exhibit ring-opening and ring-closing photoisomerization with UV/Vis light irradiation. Furthermore, their photochromic properties can be modulated by Hg2+ and F-ions. Moreover, P5 and P6 in photostationary states become promising sensors for Hg2+ and F-with high selectivity.