π-Conjugated polymeric light emitting diodes with sky-blue emission by employing thermally activated delayed fluorescence mechanism

Conjugated polymer light emitting diodes integrated with thermally activated delayed fluorescence (TADF) mechanism are attractive for display and illumination applications owing to their excellent device performance and convenient device fabrication. Whereas, there are rare reports on the conjugated TADF polymeric emitters with blue emission. Herein, a deep-blue TADF molecule, 2-(9,9-dimethyl acridan)-9,9-dimethylthioxanthene-S, S-dioxide, was incorporated into conjugated polymeric backbones through Suzuki coupling reaction with the host units of carbazole and triphenylamine derivatives to gain PCzDD-50 and PTDD-50, respectively. Despite of suffering from inevitable spectrum redshift and exciton concentration quenching, these two polymeric emitters could also exhibit sky-blue emission with the verified TADF characteristic. According to the molecular simulations and photophysical analysis, PCzDD-50 demonstrates relatively high-efficiency reverse intersystem crossing process and photoluminescence quantum yield, which can be partly ascribed to the enhanced spin orbit crossing interaction. In consistence with the PL properties, PCzDD-50 displays superior device performance with maximum external quantum efficiency (EQE) of 8.2% and Commission Internationale de L'Eclairage coordinates of (0.22, 0.35). To our best knowledge, it is the highest EQE values ever reported for TADF conjugated polymers with sky-blue emission.