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

Red-emissive fluorophores generally consist of large π-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 1 a-c are reported that consist of a very small π-system (only a single benzene) but display efficient red emission in crystals. Crystal 1 a having a molecular weight of only 252 g mol^-1 shows red emission with the maximum of 620 nm and a fluorescence quantum yield of 0.40. The unique emission property of crystal 1 a is mainly because of the planarization of skeleton dominated by the strong intramolecular hydrogen bonds and the packing structure with negligible π-π interactions contributed by the mini π-system. Moreover, besides efficient red emission, high crystallinity with co-planar facets endows crystal 1 a with significant amplified spontaneous emission.