Diboron-based Delayed Fluorescent Emitters with Orange-to-red Emission and Superior OLEDs Efficiency.

For the application of OLEDs in lighting and panels, the basic requirement is to include a full spectrum color range. Compared with the development of blue and green luminophores in thermally activated delayed fluorescence (TADF) technology, the progress of orange-to-red materials is slow and needs further investigation. In this study, three diboron compound-based materials, dPhADBA, dmAcDBA, and SpAcDBA, were designed and synthesized by nucleophilic arylation of three amine donors on 9,10-diboraanthracene (DBA) in a two-step reaction. With increasing electron-donating ability, they show orange-to-red emission with TADF characteristics. The electroluminescence (EL) of these diboron compounds exhibit emissions λmax at 613, 583, and 567 nm, for dPhADBA, dmAcDBA, and SpAcDBA, respectively. It is noteworthy that the rod-like D-A-D structures can achieve high horizontal ratios (84~86%) and outstanding device performance for orange-to-red TADF OLEDs: the highest external quantum efficiencies (ηEQE) for dPhADBA, dmAcDBA, and SpAcDBA are 11.1 ± 0.5%, 24.9 ± 0.5%, and 30.0 ± 0.8%, respectively. Therefore, these diboron-based molecules offer a promising avenue for the design of orange-to-red TADF emitters and the development of highly efficient orange-to-red OLEDs.