The Synergistic Mechanisms of AIE, ESIPT and ICT in the α-cyanostilbene-based Derivative: A Red-fluorescence Probe With a Large Stokes' Shift for Copper (II) Ion Determination and Reversible Response to Amine/acid Vapor.

Abstract

Herein, α-cyanostilbene-based luminogen with an electron donor-π-electron acceptor (D-π-A) architecture was formylated into the salicylaldehyde-analogue luminogen, followed by the Schiff base reaction with phenylamine, a red-emitting luminogen was elaborately designed and successfully synthesized in a high yield of 89%. Its well-defined structure was confirmed by FT-IR, MALDI-TOF-MS, HR-MS and 1H/13C NMR technologies. Based on the synergistic mechanisms of aggregation-induced emission (AIE), excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT), it enjoyed a red-fluorescence emission at 627 nm in THF/water mixtures (fw = 95%) and was used as a probe. Moreover, the TLC-based test strips loaded with the probe not only exhibited the reversible fluorescence response to amine/acid vapor but also showed sensitive and selective fluorescence response towards Cu2+. Furthermore, the fluorescence titration experiment between the probe and Cu2+ in THF/water mixtures (fw = 95%, pH = 7.4) revealed that the detection limit was 1.18 × 10-7 M and the binding constant was 1.59 × 105. Job's plot experiment and HR-MS analysis revealed the 2:1 binding stoichiometry of the probe with Cu2+. The method enabled real-time assessment for Cu2+ in real water samples. This study could offer insightful opinions on the development of long-wavelength emissive luminogens based on α-cyanostilbene.