White Afterglow Room‐Temperature Emission from an Isolated Single Aromatic Unit under Ambient Condition

Single aromatic structures generally do not generate emission with a white afterglow (i.e., a lifetime longer than 1 s). This study shows white afterglow room‐temperature (RT) emission from an isolated single aromatic structure doped into a rigid amorphous matrix in air. 2,5,8,11,14,17‐Hexa(4‐(2‐ethyl‐hexyl‐)‐hexa‐peri‐hexabenzocoronene (6EhHBC) doped into β‐estradiol shows blue‐green thermally activated delayed fluorescence (TADF), as well as red phosphorescence with a lifetime of 3.9 s, at RT in air. The energy difference between the lowest singlet excited state and the lowest triplet excited state (ΔE _ST) of 6EhHBC is reduced to below 0.5 eV because of the effective separation between the two molecular orbitals related to fluorescence caused by the large 2D symmetric extension of the planar aromatic cyclic structures. The long‐lived RT triplet state of 6EhHBC in the rigid host matrix enables an efficient TADF with ΔE _ST ≈ 0.5 eV at RT, as well as a red afterglow RT phosphorescence, leading to white afterglow RT emission.