Cove-Edged Boron-Doped peri-Acenes via Alkyne-Enabled Cyclization

Heteroatom-doping of polycyclic aromatic hydrocarbons may alter their electronic structures and thereby achieve intriguing physical properties. However, it is very challenging to dope the boron atom into [n,m]peri-acenes due to the synthetic difficulty and limited synthetic method. Herein, we disclose implementation of alkyne-enabled cyclization on organoborane π-system to construct cove-edged boron-doped [n,m]peri-acenes (BPAs). We synthesized two boron-containing π-systems that own the C₄₄B₂ and C₆₂B₂ polycyclic conjugated skeletons, respectively. Both of them feature two boron atoms and two cove regions at the zigzag edges, and thus may be regarded as an unprecedented kind of cove-edged BPAs. Detailed studies illustrate that these cove-edged BPAs exhibit significantly modulated electronic structures and properties, such as distinctive global aromaticity, multi-reversible redox activity and tunable photophysical properties. Notably, they exhibit the obviously stabilized molecular orbitals, especially HOMOs, further leading to the enlarged energy gaps and excellent ambient stability. Moreover, the stimulated emission (SE) and amplified spontaneous emission (ASE) properties are achieved for the C₄₄B₂ molecule, thus not only representing a new example of ASE-active organic materials but also demonstrating the promising utility in organic photonics. As revealed, the boron-doping and cove-edging both play a prominent role in producing these remarkable electronic effects and properties.

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