An AIE-active probe for selective fluorometric–colorimetric detection of HSO3− in aqueous solution and real samples

• A new AIE-active fluorescent probe HIBC. • Ratiometric detection of HSO 3 − ions in neutral aqueous solution. • The probe displays large stokes shift. • Notable color change for naked-eye recognition. • Live-cell imaging of HSO 3 − in Hela cells. We report herein a new biphenylcarbonitrile derivative, 4′-hydroxy-3′ -((2-imidazolylimino) methyl)-4-biphenyl carbonitrile (HIBC), which interestingly exhibits an aggregation-induced emission property. HIBC was employed for selective dual mode (fluorimetric and colorimetric) assay of HSO 3 − ions in nearly 100% aqueous medium at pH 7.4. The nucleophilic addition of HSO 3 − on the imino group in HIBC breaks its π-electron conjugation and results in a noticeable absorption and fluorescence spectral changes accompanied by a visible color change. Moreover, the formation of anionic addition product weakened the aggregation effect and meanwhile inhibited ESIPT process in HIBC, causing quenching of keto fluorescence of the probe. The probe shows good selectivity for HSO 3 − ions over all other competitive anions, which renders it a promising candidate for ratiometric fluorescent assay of HSO 3 − in aqueous systems. The limit of detection is 1.83 × 10 −7 mol/L. For the practical applicability, handy paper strips were fabricated from HIBC for convenient recognition of HSO 3 − . Additionally, HIBC was applied for the living HeLa cells bio-imaging.