Crystallization-induced highly efficient phosphorescence in metal-free organic phosphors

Room-temperature phosphorescence (RTP) emissions of metal-free organic materials have garnered considerable research attention from the fields of organic electronics and bioelectronics. However, achieving ultralong phosphorescence lifetimes and high quantum efficiencies of pure organic materials without relying on the heavy-atom effect remains challenging. Herein, a heavy-metal-free organic compound—1,4-phenylenebis((4-(9H-carbazol-9-yl)phenyl)methanone) (BCzPMB)—exhibiting two types of crystal structures with highly efficient afterglow features was synthesized. In these crystals, BCzPMB-DCM exhibited a high phosphorescence quantum efficiency of 9.1% and a lifetime of 368.7 ms. BCzPMB-N showed a phosphorescence quantum efficiency of 5.7% and a lifetime of 404.9 ms. Experimental and theoretical studies attributed this persistent RTP emission to intermolecular interactions, including π-π and intermolecular hydrogen bonding interactions. Additionally, the luminescence behavior of BCzPMB-DCM resembled that of BCzPMB-N after treatment with n-hexane, and a visual anticounterfeiting application instance was successfully demonstrated. Overall, the results of this study are anticipated to provide valuable insights for advancing the applications of organic luminogens with RTP properties.