Cyanide fluorescent sensors from diphenylacetylene derivatives

Abstract

A novel series cyanide fluorescence sensors (F1-F4) containing phenylene-ethynylene as fluorogenic center and salicylaldehyde as CN- receptor were successfully synthesized by using Sonogashira coupling reaction as a key synthetic step. The sensors exhibited selective fluorescence turn-on responses in contact with cyanide anion in aqueous DMSO or aqueous media containing Triton X-100 non ionic surfactant. The fluorescence turn-on signal is associated with the reduction of the quenching effect by internal charge transfer (ICT) process within the sensing molecules. Upon the addition of cyanide anion, the resonance electron withdrawing aldehyde group is converted into the corresponding cyanohydrin which is no longer capable of withdrawing the electrons by the resonance effect. F3, which contain one salisadehyde group and two phenylene-ethynylenes, gives the highest cyanide sensitivity among four compounds synthesized. The fluorescence quantum yields determined before and after the cyanide addition confirm that the fluorescence quenching by the ICT process in F3 is reduced the most. The detection limit of this cyanide sensor is 1.6 μM (42 ppb) in the aqueous media which is below the concentration limited by WHO in drinking water of 2.7 μM. The paper-based solid state sensors fabricated from F3 allow naked eye detection of cyanide anion down to 5 nanomole.