An Intelligent AIEgen with Nonmonotonic Multi-Responses to Multistimuli

Abstract

<p>Intelligent stimulus-response (S/R) systems are the basis of natural process and machine control, and have been intensively explored in biomimetic design, analytical chemistry and biological applications. However, nonmonotonic multi-S/R systems are still rarely studied so far. Now, we propose a rational design strategy to achieve such a unique S/R system by integrating opposite luminescence behaviors in one molecule. When solvent polarity increases, many heterocycles often become more emissive due to the suppression of the proximity effect. However, molecules with donor-acceptor (D-A) structures tend to be less emissive because of the twisted intramolecular charge transfer. Meanwhile, protonation on D/A moieties will weaken/strengthen the D-A interaction to result in blue/red-shifted emissions. By combining a protonatable heterocyclic acceptor and a protonatable donor together in one molecule, we can easily achieve nonmonotonic brightness responses to polarity stimuli and nonmonotonic color responses to pH stimuli. In this work, a simple molecule, namely ASQ is chosen as the model compound to verify the design strategy feasibility. It successfully shows two opposite trends of responses to polarity and pH stimuli, and aggregation-induced emission (AIE) with a nonmonotonic AIE curve. Moreover, the acidified ASQ solution is also a pure organic up-conversion and white-light-emitting system. A new mechanistic viewpoint is established to explain its unique anti-Stokes emission. Besides, ASQ shows multivalent functionalities including albumin protein sensing, ratiometric pH sensing, and amine gas sensing, etc. Therefore, ASQ is proved to be a fundamentally important and versatile functional “intelligent” AIE luminogen with nonmonotonic multi-responses to multi-stimuli. <br></p>

Spiro-fused bicyclo[3,2,2] octatriene-cored triptycene: synthesis, molecular packing, and functional aggregates

“…Unlike ACQ, molecules of AIE exhibit weak or an absence of photoluminescence when dissolved in solution but intense photoluminescence when aggregated [15]. This state-dependent phenomenon is primarily attributed to the restriction of intramolecular motions on aggregation, which limits the nonradiative leap of excited states, although other mechanistic considerations have been proposed [16][17][18][19]. After the seminal report on the polyphenyl silole system [20], multiple AIE-active molecules have been reinvestigated or newly discovered [21,22].…”