Highly sensitive and selective fluorometric off-on K+ probe constructed via host-guest molecular recognition and aggregation-induced emission

In this work, we integrated the concept of aggregation-induced emission (AIE) with the specific supramolecular recognition between K + ions and crown ether moieties to develop more effective fluorometric K + probes. We synthesized a novel crown ether-functionalized tetraphenylethene (TPE) derivative, TPE-(B15C5) 4, via the thiol-ene click reaction of thiol-derivatized TPE, TPE-(SH) 4, with maleimide-functionalized benzo-15-crown-5 (B15C5). In TPE-(B15C5) 4, the TPE core and four outer B15C5 moieties serve as the AIE-active motif and supramolecular K +-recognizing functionalities, respectively. TPE- (B15C5) 4 molecularly dissolves in THF with negligible fluorescence emission. As we have envisaged, upon K + addition, TPE-(B15C5) 4 can be effectively induced to aggregate due to K +-mediated cross-linking via the formation of K +/B15C5 (1/2 molar ratio) molecular recognition complex in a sandwiched manner. This process is concomitantly accompanied with the turn-on of fluorescence emission via the AIE mechanism. Thus, TPE-(B15C5) 4 can serve as highly sensitive and selective fluorometric off-on K + probes.