Design, synthesis, and properties of polystyrene‐based through‐space charge transfer polymers: Effect of triplet energy level of electron donor moiety on delayed fluorescence and electroluminescence performance

Two kinds of polystyrene‐based through‐space charge transfer (TSCT) polymers consisting of spatially‐separated acridan donor moieties bearing phenyl or naphthyl substituents and triazine acceptor moieties are designed and synthesized. It is found that TSCT polymers containing phenyl‐substituted acridan donors exhibit high‐lying singlet ( S 1 ) and triplet ( T 1 ) states with small singlet‐triplet energy splitting (∆ E ST ) of 0.04 – 0.05 eV, resulting in thermally activated delayed fluorescence (TADF) with reverse intersystem crossing rate constants of 1.1 – 1.2 × 10 6 s −1 . In contrast, polymers bearing naphthyl‐substituted acridan donors, although still having TSCT emission, exhibit no TADF effect because of the large ∆ E ST of 0.30 – 0.33 eV induced by low‐lying locally excited T 1 state of naphthyl donor moiety. Solution‐processed organic light‐emitting diodes using TSCT polymers containing phenyl‐substituted acridan donors reveal sky‐blue emission at 483 nm together with maximum external quantum efficiency (EQE) of 11.3%, which is about 30 times that of naphthyl‐substituted counterpart with maximum EQE of 0.38%, shedding light on the importance of high triplet energy level of donor moiety on realizing TADF effect and high device efficiency for through‐space charge transfer polymer.