Novel isocyanobenzene carbazole-based thermally activated delayed fluorophors towards solution-processed blue emitting OLED devices with high efficiency

Achieving efficient blue emission is an exigent challenge for the application of thermally activated delayed fluorescent organic light-emitting diodes (TADF-OLEDs). Carbazole benzonitrile-based TADF molecules exhibit promising performance in achieving the goal. Here, by replacing the cyano group in the sensitizer with the isocyano group, a 9 nm hypochromatic shift in photoluminescence spectra of the sensitizer and an enhanced efficiency of the Förster energy transfer (FET) in TADF-sensitized fluorescence (TSF) is found. By using the isocyano-based compounds as sensitizers, a maximum external quantum efficiency of 24.5 % is obtained in solution-processed OLEDs, surpassing the cyano-based counterparts with similar structures. Moreover, the full width at half maximum (FWHM) of the emitter in the electroluminescence spectrum is also decreased from 47 nm to 38 nm, indicating a more complete energy transfer.