Achieving Charge‐Transfer from the Boron‐Vertices of o ‐Carborane: Dual‐Emission with a Shift of 505 nm (2.1 eV)

The boron-vertices of o-carborane have long been considered to be inert in conjugation with π-substituents. Herein, we demonstrate that the boron vertices of o-carborane can be engineered to participate in intense charge-transfer (CT) transitions. Through strategic design-appending electron-donating carbazoles at the boron vertices-we synthesized three 9,12-substituted o-carboranes (1, 2a, and 2b). While 1 only shows LE emission, compounds 2a and 2b, which contain phenyl groups at the carbon vertices, show unprecedented dual emission with a colossal gap of up to 505 nm (2.1 eV) between bands. Photophysical and theoretical studies reveal that photoexcitation triggers a unidirectional conversion from a locally excited (LE) state to a CT state, yielding the first direct evidence of CT from a boron-functionalized donor into the carborane cage. This CT emission is highly sensitive to environment, exhibiting aggregation-induced emission enhancement with quantum yields reaching 80%. Our findings disrupt the longstanding carbon-centric view of carborane-based luminescence, unveiling a new strategy to activate boron-vertex participation in electronic conjugation, opening a pathway for the development of high-performance dual-emissive materials based on o-carborane.