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Designing highly efficient purely organic phosphors at room temperature remains a challenge because of fast non-radiative processes and slow intersystem crossing (ISC) rates. The majority of them emit only single component phosphorescence. Herein, we have prepared 3 isomers (o, m, p-bromophenyl)-bis(2,6-dimethylphenyl)boranes. Among the 3 isomers (o-, m- and p-BrTAB) synthesized, the ortho-one is the only one which shows dual phosphorescence, with a short lifetime of 0.8 ms and a long lifetime of 234 ms in the crystalline state at room temperature. Based on theoretical calculations and crystal structure analysis of o-BrTAB, the short lifetime component is ascribed to the T\(^M_1\) state of the monomer which emits the higher energy phosphorescence. The long-lived, lower energy phosphorescence emission is attributed to the T\(^A_1\) state of an aggregate, with multiple intermolecular interactions existing in crystalline o-BrTAB inhibiting nonradiative decay and stabilizing the triplet states efficiently.
Activating Organic Phosphorescence via Heavy Metal–π Interaction Induced Intersystem Crossing
(2022)
Heavy‐atom‐containing clusters, nanocrystals, and other semiconductors can sensitize the triplet states of their surface‐bonded chromophores, but the energy loss, such as nonradiative deactivation, often prevents the synergistic light emission in their solid‐state coassemblies. Cocrystallization allows new combinations of molecules with complementary properties for achieving functionalities not available in single components. Here, the cocrystal formation that employs platinum(II) acetylacetonate (Pt(acac)\(_{2}\)) as a triplet sensitizer and electron‐deficient 1,4,5,8‐naphthalene diimides (NDIs) as organic phosphors is reported. The hybrid cocrystals exhibit room‐temperature phosphorescence confined in the low‐lying, long‐lived triplet state of NDIs with photoluminescence (PL) quantum yield (Φ\(_{PL}\)) exceeding 25% and a phosphorescence lifetime (τ\(_{Ph}\)) of 156 µs. This remarkable PL property benefits from the noncovalent electronic and spin–orbital coupling between the constituents.