Intramolecular C−H⋅⋅⋅O Hydrogen‐Bonded Solid Emitter as Colorimetric and Fluorometric Cyanide‐Selective Chemodosimeter

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. An intramolecular C−H⋅⋅⋅O hydrogen‐bonded solid emitter (1Me) with an intramolecular charge transfer (ICT) characteristic was prepared for the colorimetric and fluorometric detection of cyanide based on an intramolecular C−H⋅⋅⋅O hydrogen‐bond on–off switching mechanism.