Achieving Charge‐Transfer from the Boron‐Vertices of <i>o</i> ‐Carborane: Dual‐Emission with a Shift of 505 nm (2.1 eV)
Xiaoyang Xu, Xueyuan Zhao, Shuang Xu, Xinning Zhang, Qihao Wang, Lin Wu, Xin Li, Junqing Shi, Jiani Ma, Lei Ji, Wei Huang
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.