Simple Acridan-Based Multi-Resonance Structures Enable Highly-Efficient Narrowband Green TADF Electroluminescence

Multi-resonance thermally activated delayed fluorescence (MR-TADF) offered exceptional solution for narrowband organic light emitting diode (OLED) devices in terms of color purity and luminescence efficiency, while the development of new MR skeleton remained an exigent task, especially for long wavelength region. We hereby demonstrate that a simple modification of the B (boron)-N (nitrogen) framework by sp3 -carbon insertion would significant bathochromic shift the short-range chargetransfer emission and improve the device performances. The bis(acridan)phenylenebased skeleton developed in this contribution presented a non-planar conformation and allowed facile introduction of isolating units to prevent triplet-involved quenching, deriving two luminophores with quantum yields approaching 90% and narrow FWMHs below 30 nm in film state. Corresponding green-emissive devices realized superior performances comparing to the planar carbazolyl-based MR-TADF analogues, with a maximum external quantum efficiency (EQEmax) up to 28.2% and small efficiency rolloff without the involvement of any sensitizing host