Carbazole Analog Doping‐Induced Bright Red and Near‐Infrared Organic Room‐Temperature Phosphorescence with Long Lifetime

Abstract Materials with room‐temperature phosphorescence (RTP) from deep red to near‐infrared (NIR) region exhibit great potential for emerging applications. However, such molecules typically require a low‐lying first triplet (T 1 ) excited state, which may not be optimal for exciton stabilization, potentially compromising the phosphorescence lifetime. This study reports the design of four 9 H ‐carbazole (Cz) analogs with extended conjugation lengths used as dopants to achieve RTP emissions in deep red and NIR regions with lifetimes exceeding 700 ms. These findings reveal that substituting reactive hydrogen atoms in Cz analogs with methyl groups significantly enhances the photoluminescence quantum yield (PLQY) of these materials compared to their non‐methylated counterparts. Additionally, these doping systems can be activated by visible light, achieving persistent phosphorescence even under the excitation of 450 nm light. Theoretical calculations demonstrate the crucial roles of charge transfer state and the enhanced spin‐orbital coupling (SOC) matrix elements upon doping for achieving long‐lifetime phosphorescence beyond 600 nm. This research presents a strategy employing Cz‐based doping systems to facilitate RTP emissions extending from visible to deep red and NIR regions.