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

Abstract

Abstract 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.