Recent Advances in Materials with Room-Temperature Phosphorescence: Photophysics for Triplet Exciton Stabilization

Room-temperature phosphorescence (RTP), which has a much longer emission lifetime than fluorescence, often enables unique material characteristics and fabrication of state-of-the-art optoelectronic devices that cannot be realized using conventional fluorescent materials. The triplet exciton characteristics related to the appearance of efficient RTP also often provide intrinsic intra-and inter-molecular physical information about the materials. This article reviews recently reported aromatic materials that present RTP characteristics. Various aromatic materials with RTP characteristics are classified in terms of their radiative rates and radiationless rates from the lowest triplet excited state (T1) while taking the presence and absence of heavy atoms and charge transfer characteristics at T1 into consideration. Statistical arrangements based on physical factors of RTP materials indicate that the recent appearance of RTP in various metal-free aromatic structures is related to a large reduction in quenching caused by strong intermolecular interaction between the aromatics and the surrounding materials; additionally, intrinsic factors of the aromatics including the radiative rate and the nonradiative rate caused by intramolecular vibration are still not well controlled. Intrinsic control of these rates is important for overall control of the RTP yield and lifetime for potential material applications. Finally, recent applications using the RTP characteristics are highlighted.