Efficient Red-Emissive Organic Crystals with Amplified Spontaneous Emissions Based on a Single Benzene Framework

Red-emissive fluorophores generally consist of large pi-extended systems and thus encounter the problem of serious fluorescence quenching in the solid state. A series of structurally simple compounds 2,5-bis(alkylamino)terephthalates 1a-c are reported that consist of a very small pi-system (only a single benzene) but display efficient red emission in crystals. Crystal 1a having a molecular weight of only 252 gmol(-1) shows red emission with the maximum of 620 nm and a fluorescence quantum yield of 0.40. The unique emission property of crystal 1a is mainly because of the planarization of skeleton dominated by the strong intramolecular hydrogen bonds and the packing structure with negligible pi-pi interactions contributed by the mini pi-system. Moreover, besides efficient red emission, high crystallinity with co-planar facets endows crystal 1a with significant amplified spontaneous emission.