Star-Shaped ESIPT-Active Mechanoresponsive Luminescent AIEgen and Its On–Off–On Emissive Response to Cu²⁺/S^2–

Abstract

Design and development of multifunctional materials have drawn incredible attraction in recent years. Herein, we report the design and construction of versatile star-shaped intramolecular charge transfer (ICT)-coupled excited-state intramolecular proton transfer (ESIPT)-active mechanoresponsive and aggregation-induced emissive (AIE) luminogen triaminoguanidine-diethylaminophenol ( LH 3 ) conjugate from simple precursors triaminoguanidine hydrochloride and 4-( N , N -diethylamino)salicylaldehyde. Solvent-dependent dual emission in nonpolar to polar protic solvents implies the presence of ICT-coupled ESIPT features in the excited state. Aggregation-enhanced emissive feature of LH 3 was established in the CH 3 CN/water mixture. Furthermore, this compound exhibits mechanochromic fluorescence behavior upon external grinding. Fluorescence microscopy images of pristine, crystal, and crushed crystals confirm the naked-eye mechanoresponsive characteristics of LH 3 . In addition, LH 3 selectively sensed a Cu 2+ ion through a colorimetric and fluorescence “turn-off” route, and subsequently, the LH 3 -Cu 2+ ensemble could act as a selective and sensitive sensor for S 2– in a “turn-on” fluorescence manner via a metal displacement approach. Reversible “turn-off–turn-on” features of LH 3 with Cu 2+ /S 2– ions were efficiently demonstrated to construct the IMPLICATION logic gate function. The Cu 2+ /S 2– -responsive sensing behavior of LH 3 was established in the paper strip experiment also, which can easily be characterized by the naked eye under daylight as well as a UV lamp (λ = 365 nm).

Trace-Level Humidity Sensing from Commercial Organic Solvents and Food Products by an AIE/ESIPT-Triggered Piezochromic Luminogen and ppb-Level “OFF–ON–OFF” Sensing of Cu2+: A Combined Experimental and Theoretical Outcome

“…From Figure D, it can be inferred that with the increasing glycerol fraction, more specifically with the increasing viscosity, there occurs fluorescence enhancement, owing to the suppression of the intramolecular rotation, followed by facile ESIPT, making the molecule highly emissive. Thus, the analyses further validate the AIE-induced fluorescence enhancement by the RIR mechanism. , Interestingly, in Figure S14, SI, it can be observed that with the increasing concentration of NAP-1 at room temperature from 0.1 to 100 μM, the intensity of the keto emission band is increased with a gradual decrease of the enol emission band. This speculates that in the excited state a facile proton transfer process takes place with the increasing concentration or aggregation of the compound, thereby facilitating the AIE-induced emission through RIR .…”

ESIPT‐based AIE luminogens: Design strategies, applications, and mechanisms

“…Therefore, almost all the reported ESIPT‐based AIEgens for detection of metal cations involve SSB or SAA scaffolds, or at least, involve Schiff base or azine bearing an intramolecular hydrogen bond O─H···N. [ 28–57 ]…”

“…The development of ESIPT‐based AIEgens has attracted great attention in the fields of physics, chemistry, and biology science. A growing number of ESIPT‐based AIEgens have been developed and applied in the detection of cations, [ 28–57 ] anions, [ 34, 35, 41, 43, 58–68 ] and small molecules, [ 69–76 ] bioimaging in the living cell and in vivo, [ 77–116 ] drug delivery systems (DDS), [ 44, 117–119 ] liquid crystal, [ 120–122 ] white light emitters, [ 123–127 ] and latent fingerprinting. [ 56, 128–131 ]…”

A salicylaldehyde benzoyl hydrazone based near-infrared probe for copper(ii) and its bioimaging applications

“…In addition, these compounds display keto-enol tautomerism, and both the nitrogen atom and oxygen atom in the Schiff bases can act as ligand donors for Cu 2+ and consequently produce stable coordination complexes via coordination effects. 40,41 The phenol group in phenol-based Schiff base units is deprotonated in the coordination process, which could diminish the electrondonating ability of the oxygen atom. [42][43][44][45][46] Moreover, it has been reported that the uorescence signal of hemicyanine-based NIR uorophores could be turned in a controllable manner by diminishing the electron-donating ability of the oxygen atom in its phenol group.…”