Construction Of Triazine-and Corrole-based Covalent Organic Frameworks For Fluorescence Detection

Although most pollutants exist in low concentrations,many of them have considerable toxicological problems that pose a potential hazard to humans and other life forms.Examples include heavy metal ions(e.g.,Cu(II),Cr(III))and various organic compounds(e.g.,organic explosives).Therefore,it is urgent to develop sensors with high sensitivity and selectivity for specific pollutants.As a newly emerging kind of porous material,covalent organic frameworks(COFs)have drawn much attention to their sensing application because of their fascinating structural features.A novel flexible 2D COF(DTZ-COF)was synthesized using two ?-electron deficient triazine monomers rather than the commonly used one ?-electron rich fused aromatic ring under solvothermal conditions.Fortunately,DTZ-COF exhibits excellent crystallinity and high surface area,which are rarely observed in previously reported flexible 2D COFs.The comparison between flexible DTZ-COF and a non-flexible 2D TPT-TPT-COF with a similar framework suggests that the introduction of flexible building units can indeed improve the photoluminescence(PL)efficiency.The ?-electron deficient DTZ-COF has excellent fluorescence performance and exhibits unique solvent responsiveness.As a chemical sensor for detection of picric acid(2,4,6-trinitrophenol,TNP),the efficient fluorescence quenching involving both static and dynamic behavior ensures the high selectivity and sensitivity(ppb level).A new corrole-based covalent organic framework(Cor Me O-COF)with good crystallinity and high porosity was also designed and synthesized.Cor Me O-COF can detect Cu(II)with high sensitivity and selectivity based on the efficient fluorescence quenching caused by photoinduced electron transfer(PET)process.Moreover,Cor Me O-COF can selectively detect trivalent metal ions with fluorescence enhancement,such as Ga(III),Al(III),Cr(III)and Fe(III).In-depth mechanism study revealed that the binding of metal ions on the skeleton can inhibit the aggregation-caused quenching(ACQ)resulting in the improved PL efficiency.These results point out a new direction for using corrole-based COFs materials as efficient chemosensors to detect trace amount of metal ions in the environmental and biological systems.