An AIE-Active Tetraphenylethylene-Based Cyclic Urea as a Selective and Efficient Optical and Colorimetric Chemosensor for Fluoride Ions

摘要

Anion sensing is a very challenging and important issue in many diverse fields,including biological,medical and environmental sciences.In this paper,we report the serendipitous synthesis of a tetraphenylethylene(TPE)bearing a cyclic urea(coded as: 1).This easy-to-make,simple chemosensor shows high selectivity towards fluoride(F~-)ions.Importantly,this work demonstrates two important factors: firstly,the use of cyclic urea for ion sensing and secondly,the use of aggregation induced emission(AIE)-TPE signalling units.This selective fluoride sensing can be observed by the naked eye,UV-vis absorption,fluorescence spectroscopy,and 1H-NMR spectroscopy.Solutions of sensor 1 are fluorescent in DMSO with fluorescence quantum yield Φ=1.3 and upon addition of fluoride ions the emission is quenched with ΦF=0.07.Notably,other anions,such as CN~-,AcO~-,NO_3 ~-,H2PO4 ~-,HSO4 ~-,I~-,OH~-,ClO_4~-,SCN~-and Cl~-,do not show any quenching effect.The binding constant(K)between sensor 1 and fluoride was found to be 4.90×10~8 M~(-2)with a detection limit of 30 μM.We also studied AIE-activity of 1 in THF/water mixture.As such the fluorescence quantum yield(ΦF)of 1 in pure THF solution shown to be 0.05% which was enhanced 22-fold to 1.98 and 6.65% at fw=90 and 99%,respectively.This is clear confirmation that compound 1 is AIE active due to decreased solubility and increased molecular self-assembly as the water fraction is increased.