Bright Benzindolo-Benzochalcogenazolo-Based N , N -Coordinated Difluoroboron Complexes Exhibiting Yellow Electroluminescence Targeting White Organic Light Emitting Diodes

Three benzindolo−benzochalcogenazolo-based boron difluoride complexes (bI-NNB-bCh) incorporating benzoxazole, benzothiazole, and benzoselenazole acceptor units were synthesized and studied as emissive materials for organic light-emitting diodes (OLEDs). The compounds exhibit favorable electrochemical and photophysical properties, enabling their integration into vacuum-deposited OLEDs. Devices employing a conventional OLED host produce yellow−green electroluminescence with external quantum efficiencies (EQEmax) of 3.80%. Among the investigated emitters, the benzothiazole derivative delivers the best device performance, consistently with its higher photoluminescence quantum yield of 96% in the polymeric matrix. Replacing an OLED host exhibiting thermally activated delayed fluorescence results in near-white electroluminescence, demonstrating the critical influence of host−guest interactions and excited-state environments on emission characteristics. Under these conditions, close to 25% enhancement of EQEmax was achieved for the benzothiazole-based devices emitting near-white electroluminescence with color coordinates of (0.38; 0.42). These results highlight heteroaromatic acceptor engineering within the bI-NNB-bCh framework as an effective strategy for tuning photophysical properties and OLED performance.