Unlocking Room‐Temperature Phosphorescence of Polycyclic Aromatic Hydrocarbons and Beyond via External Heavy‐Atom Engineering

Abstract Room‐temperature phosphorescence (RTP) from purely organic materials holds great potential for optoelectronic and bioimaging applications; however, its realization remains challenging due to inefficient intersystem crossing (ISC) and rapid nonradiative decay. Herein, we present an effective strategy to activate and enhance RTP in heavy‐atom‐free chromophores through external heavy‐atom engineering (HAE). By dispersing these chromophores within hydrophobic halogen‐rich polymer matrices, external HAE is employed to enhance spin–orbit coupling and promote efficient ISC. The generality of this strategy is demonstrated across a series of polycyclic aromatic hydrocarbons and further extended to other heterocyclic chromophores, affording bright (phosphorescence quantum yields up to 61.6%) and long‐lived (phosphorescence lifetimes up to 273 ms) RTP materials under ambient conditions, with emission wavelengths spanning from 500 to 700 nm. This supramolecular approach circumvents the need for covalent introduction of heavy atoms to the luminophores, thereby preserving their intrinsic photophysical properties while unlocking desirable triplet‐state emissions. Overall, the current external HAE strategy provides a versatile platform for the construction of high‐performance organic RTP materials, offering new insights into the design principles of organic RTP systems and broadening the material landscape for optoelectronic and bioimaging applications.