Fluorescence from pentacyanopropenide aggregates in melamine

Aggregation-induced optical properties of molecules are at the forefront of materials sciences. Here, tetracyanoethylene (TCNE) is reacted and encapsulated in melamine. Crystallization in aqueous tetrahydrofuran solutions of melamine and TCNE at different concentrations yields colorful crystals with fluorescence emission at multiple wavelengths. Combined infrared spectroscopy and mass spectrometry reveal that the crystals are melamine doped with a trace amount of 1,1,2,3,3,-pentacyanopropenide. The fluorescence excitation-emission spectral mapping elucidates concentration dependences of the fluorescence emission in both precursor solutions and crystals. Based on density functional theory calculations the multi-wavelength emissions can be attributed to aggregates of the pentacyanopropenide. Highly stable doped melamines have the potential as multifunctional optical materials in optielectronics.