Phenanthroimidazole and dicyanovinyl-substituted triphenylamine for the selective detection of CN−: DFT calculations and practically applications

A novel CN− selective fluorescent turn-on sensor (TPMN) possessing triphenylamine and phenanthroimidazole as signaling units and dicyanovinyl unit for the binding site was designed and synthesized. TPMN exhibited a drastic change in its emission spectra with about 13-fold fluorescence enhancement when treated with CN−, while other tested anions could not arouse the fluorescence enhancement. The experimental and theoretical calculation results showed that this increase in fluorescence intensity of TPMN in presence of CN− is due to the large decrease in the ICT effect by the addition of CN− ion to β-carbon of the dicyanovinyl moiety. TPMN could selectively detect CN− with a detection limit of 0.23 μM among the common anions. The CN−-binding mode was well-characterized to be 1:1 by using Job's plot with an association constant of 5.36 (logKa). Besides, the possible utilization ofTPMN was successively tested in water samples and test kits.