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

Abstract

AbstractAnion 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−, NO3−, H2PO4−, HSO4−, I−, OH−, ClO4−, SCN− and Cl−, do not show any quenching effect. The binding constant (K) between sensor 1 and fluoride was found to be 4.90×108 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.