New luminescent compounds consisting of 10H-phenoxaboryl group as an electron-accepting unit and carbazole (9), 9,9dimethylacridane (10), or phenoxazine (11) as an electron-donating unit have been synthesized. Compounds 10 and 11 showed thermally activated delayed fluorescence (TADF) with light blue and green emissions, respectively, with very high PL quantum yields (PLQYs), however, compound 9 exhibited only a prompt emission and no delayed component. Photoluminescence studies and quantum chemical calculation based on density functional theory (DFT) and timedependent density functional theory (TD-DFT) revealed that in comparison with compound 9, HOMO and LUMO for compounds 10 and 11 are well separated, resulting in lowering ∆EST and effective reverse intersystem crossing (RISC) between a lowest triplet excited state (T1) and a lowest singlet excited state (S1). Organic light-emitting diodes (OLEDs) using compounds 10 and 11 exhibited light blue and green emissions with very good maximum ηext of 15.1% and 22.1%, respectively.

An oxygen-bridged planarized triphenylborane has been successfully synthesized. X-ray crystallographic analysis revealed that the molecule has a complete planarized structure and the shortest C-B bonds among the triarylboranes synthesized to date.

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