Boron is an electron-deficient element possessing only three valence electrons, and is highly unusual in that its trivalent, three-coordinate compounds—despite not satisfying the octet rule—can exist in a stable form. Unlike its group 13 counterparts such as aluminum and gallium, boron forms sufficiently strong covalent bonds with carbon and other elements, enabling the synthesis of boron-containing organic compounds that can be handled in much the same way as conventional organic molecules, provided that appropriate molecular design is employed.

Because tricoordinate boron possesses an empty 2p orbital, its incorporation into π-conjugated systems leads to 2p(B)–π conjugation, which gives rise to a variety of unique functions: optical absorption and emission properties resulting from a lowered LUMO energy level, donor–π–acceptor (D–π–A) conjugation with electron-donating groups, and molecular switching behavior triggered by Lewis base coordination to the vacant orbital.

We focus on the aforementioned 2p(B)–π conjugation and aim to develop optoelectronic functional molecules based on electronic interactions between boron, π-conjugated systems, and main-group elements. Using dibenzoheteraborins—rigid and robust fused π-conjugated frameworks incorporating boron along with donor-type main-group elements such as nitrogen or sulfur—as the central scaffold, we have developed a range of functional molecules, including fluorescent emitters, anion sensors, and phosphorescent compounds. 

We have developed blue emitters for organic light-emitting diodes (OLEDs) by harnessing the optical properties of dibenzoheteraborins. These emitters exhibit excellent thermally activated delayed fluorescence (TADF) characteristics and maintain high quantum efficiency even under high-brightness, high-current-density operation in OLED devices. This demonstrates that the dibenzoheteraborin framework is effective in suppressing efficiency roll-off in OLEDs. In the excited state, the TADF properties are enhanced through electronic interactions between multiple heteraborin units.

We are also exploring the development of ultraviolet (UV) emitters based on the dibenzoheteraborin framework, white-emitting molecules utilizing dual emission, and phosphorescent emitters that leverage the heavy atom effect of chalcogens. In addition, we are investigating the application of dibenzoheteraborins in organic photocatalysis.