Reversible pH switchable aggregation-induced emission of self-assembled benzimidazole-based acrylonitrile dye in aqueous solution

Abstract

We report the pH switchable fluorescence and aggregation-deaggregation behaviour of a 2-benzimidazolyl substituted acrylonitrile dye (BIA). From the single molecular entity, three prototropic species (tri-state system) are derived that respectively emit in the red, green and cyan spectral regions. The neutral form is capable of self-assembly in an aqueous environment exhibiting stable red-orange aggregation-induced emission (AIE) at 600 nm in the physiologically relevant pH range. The aggregation and emission are pH switchable and fully-reversible. The molecule is shown to similarly function in the solid state where its emission can be modulated by exposure to acidic and basic vapours. Multicolour and reversibly pH switchable tri-state emission from a single fluorophore containing a biologically active benzimidazole moiety can find application in ratiometric optical chemosensing, bioimaging and functional materials.