A ratiometric fluorescent probe for bisulphite anion, employing intramolecular charge transfer

4-(1H-benzimidazol-2-yl)benzaldehyde (1) has been developed as a new ratiometric fluorescent probe for bisulphite, based on the modulation of intramolecular charge transfer (ICT). Upon mixing with bisulphite in aqueous ethanol, an aldehydebisulphite adduct was formed and the ICT of the probe was switched off, which resulted in a ratiometric fluorescence response with an enhancement of the ratios of emission intensities at 368 and 498nm. The detection range of the probe for bisulphite is in the 2.0200 mu mol/L concentration range and the detection limit is 0.4 mu mol/L. Probe 1 produces a ratiometric fluorescent response to bisulphite with a marked emission wavelength shift (130nm) and displays high selectivity for bisulphite over other anions. Copyright (c) 2012 John Wiley & Sons, Ltd.