Fluoride-regulated colorimetric and fluorometric switch through B-F dynamic covalent reactions of AIEgens

It is extremely challenging to design external stimuli-controlled molecular switches with absorption and fluorescence dual-mode outputs that are suited for diverse states. Herein, we propose a general molecular design strategy for achieving fluoride-regulated colorimetric and fluorometric switches based on B-F dynamic covalent reactions by introducing borate units into AIE-active molecular skeletons. A group of fluoride-responsive smart molecules was designed by introducing one or two borate units into the typical aggregation-induced emission molecular skeleton tetraphenylethene, all of which can be combined with fluoride ions to form stable products with sharp color and fluorescence changes. It is proved that the addition of fluoride ions onto the boron center can regulate the photophysical behaviour of these compounds, and the AIE activity of these compounds enables them to perform well in a solid matrix, which is more desirable in diverse practical applications. Their fluoride-responsive photophysical behaviour and AIE activity provide an opportunity to develop a quantitative detection method for fluoride ions with high selectivity and high sensitivity both in solution and on a solid matrix-like test strip, which greatly simplifies the recognition of fluoride ions. The dynamic nature of the B-F covalent reaction and the multicolor switching behaviour of these smart molecules was demonstrated in controllable colorful patterning and advanced data encryption with excellent performance. This study highlights that the combination of the B-F dynamic covalent reaction and the AIEgens can greatly expand fluoride-responsive smart molecules from only solution-based fluoride sensing to diverse surface/interface-involved applications in dual-mode signaling.