A novel and simple fluorescent and colorimetric primary chemosensor based on Congo-Red for sulfite and resultant complex as secondary fluorescent chemosensor towards carbonate ions: Fluorescent probe mimicking INHIBIT logic gate.

A simple receptor based on Congo-Red (CR) was prepared by complexation of CR into two equivalents of Cu (II) ([CR-(Cu)2]) and it has been designed for detection of sulfite and carbonate ions. This chemosensor exhibits high sensitivity for sulfite over other anions in aqueous buffer solution. It exhibits colorimetric 'naked eye' and fluorometric responses to SO3(2-) which results from the addition of SO3(2)(-) to CR diazo moiety. Hereupon, CO3(2-) greatly limits the fluorescence of the resultant sulfite-receptor complex via a hydrogen bonding interaction ([CR-(Cu)2]-SO3). This system can be applied for selective detection of CO3(2-) in the presence of other anions. The detection limits of SO3(2-), calculated by the colorimetric and fluorometric methods, were found to be 0.07 and 0.09µmolL(-)(1), respectively. The sulfite-receptor complex also displayed the ability to detect up to 0.06µmolL(-)(1) CO3(2-). The fluorescence output mimicked 'INHIBIT' logic gate function. The output was exhibited by the intramolecular charge transfer of the [CR-(Cu)2] probe, and was provided by chemical inputs (SO3(2-) and CO3(2-)).