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 pi-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 4 pi 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 pi-systems.