Intramolecular C-H⋅⋅⋅O Hydrogen-Bonded Solid Emitter as Colorimetric and Fluorometric Cyanide-Selective...

An indole-indanedione-based small molecule, compound 1Me, comprising an intramolecular C-H⋅⋅⋅O hydrogen-bond (H-bond) and with an intramolecular charge transfer (ICT) characteristic was prepared for the colorimetric and fluorometric detection of CN^- . Compound 1Me is virtually nonfluorescent in solution but emits a strong yellow fluorescence in the solid state because of the intramolecular C-H⋅⋅⋅O H-bond, which inhibits the free rotation of the exocyclic C-C single bond of 1Me. The nucleophilic addition of CN^- to the β-conjugated carbon of the indanedione group of 1Me, which breaks the intramolecular C-H⋅⋅⋅O H-bond and blocks ICT, causes the colorimetric and fluorometric responses of 1Me to CN^- . Furthermore, inexpensive and portable paper-based test kits containing 1Me could be used to rapidly and conveniently sense CN^- using the naked eye in real time. The results provide a new strategy for designing colorimetric and fluorometric cyanide-selective sensors based on an intramolecular C-H⋅⋅⋅O hydrogen bonded solid emitter.