Switching of Reverse Charge Transfers for a Rational Design of an OFF-ON Phosphorescent Chemodosimeter of Cyanide Anions

A rational approach to luminescence turn-on sensing of cyanide by a dicyanovinyl-substituted acetylide Pt(II) complex, which primarily relies on the nucleophilic addition reaction of cyanide anions to the alpha-position of the dicyanovinyl group, is described. The strategy used for the design of this cyanide-selective sensor takes advantage of a switch of charge transfer from ML'CT to MLCT/L'LCT in this acetylicle Pt(II) sensor. As a result, this chromophore that exhibits almost no basal luminescence displays observable changes in its UV-visible spectrum and acquires strong phosphorescence upon addition of cyanide anions. DFT computations reveal that the frontier molecular orbitals of the anionic system obtained after addition of CN- are drastically different from those of the neutral initial species. TD-DFT computations permitted a full assignment of the observed absorption bands and explained well the emissive properties of the species under consideration.