Low‐Molecular‐Weight J‐Aggregate Solid Red Emitter for Selective and Quantitative Detection of Cyanide.

A dimethylaniline (donor)‐indanedione (acceptor) conjugate (sensor 1) with a very low molecular weight of 277 g mol−1 and intramolecular charge transfer (ICT) characteristics was synthesized. Sensor 1 shows weak ICT fluorescence in solution, but strong emission (Φ=16%) in the solid state owing to intramolecular and intermolecular C−H⋅⋅⋅O hydrogen bonds that inhibit the free rotation of the exocyclic C−C single bond. Compared to yellow emitter 1Y, which has a similar donor‐acceptor structure, sensor 1 shows red fluorescence in the solid state owing to J‐aggregate formation. The colorimetric and fluorometric responses of sensor 1 to cyanide in both solution and solid state are due to the nucleophilic addition of cyanide to the β‐conjugated carbon of the indanedione group, which prohibits ICT. Additionally, inexpensive portable paper‐based test kits based on sensor 1 were easily prepared and could be used for fast and quantitative naked‐eye cyanide detection in real time. [ABSTRACT FROM AUTHOR]