Temperature-Independent Ultralong Organic Phosphorescence with a Symmetrical Butterfly-Type Structure

Room-temperature phosphorescence (RTP) materials in the solid state have been attracting widespread attention and found broad prospects in the fields of smart wear, optoelectronic devices, bioimaging, and encryption. However, purely organic RTP materials are still scarce due to weak spin–orbit coupling and fast nonradiative transition under ambient conditions. Here, we developed a facile strategy using the heavy-atom effect to construct RTP materials of commercial/lab-synthesized carbazole-based derivatives (DCzB-X/DCzB-X-lab). DCzB-Cl, DCzB-Br, and DCzB-I synthesized with commercial carbazole have ultralong phosphorescence lifetimes of 789.0, 184.3, and 49.6 ms, respectively, much longer than those of lab-synthesized carbazole derivative due to the presence of isomers in the commercial samples. Combined with the single-crystal structure and theoretical calculation analysis, the compact packing mode of the butterfly-type packing style (BPS) with a halogen substituent is favorable for persistent phosphorescence. Impressively, an unusual phenomenon was found, which shows that the phosphorescence lifetime of DCzB-halogen does not increase with the decrease of temperature, indicating that BPS can effectively suppress the nonradiative transition. The results break through the traditional low-temperature-enhanced phosphorescence theory and provide a new platform to rationally design highly efficient RTP materials.