Cocrystallization‐Induced Red Ultralong Organic Phosphorescence

Organic cocrystals formed through multicomponent self‐assembly have attracted significant interest owing to their clear structure and tunable optical properties. However, most cocrystal systems suffer from inefficient long‐wavelength emission and low phosphorescence efficiency due to strong non‐radiative processes governed by the energy gap law. Herein, an efficient long‐lived red afterglow is achieved using a pyrene (Py) cocrystal system incorporating a second component (NPYC4) with thermally activated delayed fluorescence (TADF) and ultralong organic phosphorescence (UOP) properties. The cocrystal (NPYC4‐Py) not only inherits the excellent luminescence of its monomeric counterparts, but also exhibits unique dual‐mode characteristics, including persistent TADF and UOP emission with a high quantum yield of 58% and a lifetime of 362 ms. The precise cocrystal stacking distinctly reveals that intermolecular interactions lock the cocrystal formation and weaken the intermolecular π‐π interactions between NPYC4 and Py, thereby stabilizing the excited triplet excitons. Furthermore, the favorable energy level of NPYC4 acts as a bridge, reducing the energy gap between the S1 and T1 states for Py, therefore activating its red phosphorescence from Py. This research provides direct insights into achieving efficient red UOP through co‐crystallization.