Aggregation-induced emission switch showing high contrast mehanofluorochromism and solvatofluorochromism: Specifically detects HSO₃⁻ in bioimaging studies

In this work, a novel mechanoresponsive luminescent (MRL) and aggregation induced emission (AIE) switch, 2-(4-((9-butyl-9H-carbazol-3-yl)ethynyl)benzylidene)malononitrile (CABM) has been synthesized by a perfect blending of the carbazole-based triple bond and benzyl malononitrile conjugated derivative via the ‘sonogashira coupling reaction’. The optoelectronic properties of this donor–π–acceptor (D–π–A) framework spontaneously originates a prominent yellow fluorescence which further exhibits a mechanical stimuli induced orange – red emission. Interestingly, just after fumed with dichloromethane (DCM) vapor, the rubbed CABM powder facilely exhibits a restoration in the emission profile as well as fluorescence color. Moreover, this multidimensional switch, CABM shows a prominent solvent dependent sensitivity towards different polarities of organic solvents. CABM also exhibits a typical intramolecular charge transfer (ICT) mechanism along with AIE behaviors with high solid-state efficiency. Importantly, CABM acts as a fluorescence indicator for the qualitative and quantitative detection of low-level water content as impurity in organic solvent. CABM is also found to specifically sense HSO₃⁻ anion compared to other guest anions. These promising observations inspire us for the bioimaging studies by using human blood cells which clearly exhibit that CABM can be used to detect HSO₃⁻ in human peripheral blood mononuclear cells (PBMCs).