Dual‐Locking Strategy for Highly Bright and Ultralong Red Room‐Temperature Phosphorescence Enabling Unconventional Time‐Dependent Afterglow

Red organic room‐temperature phosphorescence (ORTP) materials with both high brightness and ultralong lifetime are still rare due to the energy gap law. Currently, most reported red phosphors are rigid polycyclic aromatic hydrocarbons (PAHs). In this research, a non‐PAH merocyanine with pure π‐π* transition character (NBMCy‐B4) was designed to render the red phosphor an inherently long τ P . Meanwhile, a dual‐locking strategy featuring molecular‐engineered double intramolecular H ‐bonds and a new quasi‐planar benzocycloketone (5‐methoxytetralone, 5M‐TL) host matrix effectively protected the vulnerable red triplet excitons from nonradiative transitions, promoted the triplet–triplet energy transfer (TTET, 350 nm excitation), and dramatically boosted the Φ P and τ P of NBMCy‐B4/5M‐TL to 12.3% and 794 ms, which surpass those of most red PAH afterglow materials. Furthermore, the intrinsic intersystem crossing (ISC) of NBMCy‐B4 enables its excitation by 488 nm visible light, making it a special type of red ORTP material that has a dual‐mode excitation capability based on two distinct triplet‐yielding pathways. When doped in 5M‐TL, analogous merocyanines with different N ‐Me benzoheterocycles (NBMCy‐B1‒B3) emitted multicolored RTP. Codoping of short‐lived NBMCy‐B2 (green) and long‐lived B4 (red) in 5M‐TL afforded an unconventional and color‐tunable time‐dependent afterglow material with unique practical value in dynamic afterglow anti‐counterfeiting.