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 ( increment 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 x 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 increment 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.