Intermolecular charge transfer as an excited-state modulator for dual delayed luminescence in doping systems

Research on multifunctional luminescent materials is highly intriguing due to their wide-ranging applications in display technology, data security, and bioimaging. Nonetheless, achieving dual-mode delayed luminescence materials that simultaneously integrate thermally activated delayed fluorescence (TADF) and organic room-temperature phosphorescence (RTP) using pure organic small molecule remains a significant challenge. Herein, we report a host-guest system composed of polyaromatic hydrocarbons (PAHs) as guest emitters embedded within a benzophenone (BP) matrix, which successfully realizes efficient dual emission of TADF and RTP. The charge-transfer (CT) state functions as an "energy redistribution hub", playing a critical role in promoting both reverse intersystem crossing (RISC) and internal conversion (IC), thereby enabling the coexistence of TADF and RTP. Ultrafast spectroscopic analysis confirms that the decay of anion and cation radicals occurs on a comparable timescale, supporting the CT-mediated mechanism. The developed material exhibits several characteristics, including an ultralong RTP lifetime, tunable emission from green to near-infrared, and high photoluminescence quantum efficiency. Notably, these properties are retained even in nanocrystalline form, demonstrating their strong potential for bioimaging applications. This study provides an effective strategy for designing purely organic dual-mode luminescent materials and opens up promising avenues for their future applications.