Boron-Doped Molecular Carbons Bearing a Formal Boron-Inserted Pentalene: Synthesis, Electronic Structures and Properties

Two boron-doped molecular carbons (BMCs), featuring one formal boron-inserted pentalene (BP) embedded into the C₂₀B or C₂₈B polycyclic π-skeleton, were successfully synthesized. Despite their small-size conjugated structures, both of them exhibit unusual broad light absorption, narrow energy gaps, and electron-accepting ability, as well as local antiaromaticity with pseudo 4π electrons. As disclosed, these intriguing physical properties are significantly contributed by the boron atom and pentagonal ring in the BP substructure, thus demonstrating the importance of such BP incorporation into polycyclic π-systems.