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.