Promising four-coordinated organoboron emitters for organic light-emitting diodes

Four-coordinated organoboron compounds have drawn intense attention as light-emitting and/or electron-transporting layers in organic light-emitting diodes (OLEDs) due to their remarkable solid-state luminescence and electron-transporting properties. During the past dozen years, by exploring the conjugating ligand moieties, a variety of fascinating four-coordinated boron-containing compounds have been constructed, mainly including N,O (nitrogen, oxygen)-, N,N-, O,O-chelated types. These compounds are promising emissive materials for OLEDs: they have been shown to be superior highly efficient and full-colour emitters for OLEDs with some TADF emitters based on these ligands achieving high external quantum efficiencies over 20% in devices. This review focuses on the significant advances in four-coordinated organoboron emitters over the past dozen years, with emphases on material design and OLED performance. The molecular structures summarized here are comprehensive and up-to-date, covering compounds with traditional fluorescence, phosphorescence, and thermal-activated delayed fluorescence (TADF).