Highly emissive hierarchical uniform dialkylfluorene-based dimer microcrystals for ultraviolet organic laser

The hierarchically uniform condensed structure of light-emitting conjugated molecules is an effective platform to obtain an excellent electronic landscape with little physical defect and further improve the photophysical property. Herein, a highly emissive dialkylfluorene-based dimer crystal structure is constructed with crystalline-enhanced emission for ultraviolet organic microlasers. Instable planar conformation of a fluorene dimer can be stabilized in a rigid crystalline framework, which is a fundamental factor to fabricate the hierarchically uniform structure (including planar conformational molecules and periodical molecular packing in the crystalline structure). Therefore, a high photoluminescence quantum efficiency of 50 and 75% is obtained for neat spin-coated films and single crystals, respectively, attributing to the little physical defect in this hierarchical oriented structure. This robust crystalline-enhanced emission enables their microcrystals to construct ultraviolet organic lasers (395 nm) with a low threshold of 7.65 × 10^-3 nJ cm^-2 pulse^-1, which is 4 times lower than that of the controlled trimer one (TDMeF). These observations reasonably confirm that the hierarchically ordered architecture of conjugated materials shows great promise in optoelectronic applications.