Effectively Unlocking the Potential Molecular Room Temperature Phosphorescence of Pure Carbazole Derivatives

Abstract The current prevailing views are that carbazole derivatives without isomers show inferior room temperature phosphorescence (RTP) and that N‐ aryl carbazole derivatives exhibit no ultralong RTP in dilute film states since the distorted structures easily dissipate the excitation energy. In the current work, we present that doping N‐aryl carbazole derivatives with heteroatoms and/or heavy halogen into PMMA at the molecular level by thermoplasticizing solution‐cast films can achieve ultra‐long‐lived (>1 s) and highly‐efficient (>36%) molecular RTP without the need of crystallization and isomer doping. Unlike isomer‐doped crystals that almost all emit yellow RTP, the RTP colors of doped PMMA films depend on the molecular structures of carbazole derivatives. Also, we can realize highly efficient and long‐lived red fluorescence afterglow via persistent Förster resonance energy transfer from RTP emission to fluorescent emitter. These colorful afterglow polymer films exhibit an ultra‐long (>20 h) photo‐activation pattern memory effect. This work has challenged existing experimental results and relative RTP mechanisms, providing a reasonable processing strategy for manifesting and enhancing the deserved RTP properties of organic doped polymers.