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.