Globally Aromatic 10-Boratetraoxacorroles: Boron-Doped Macrocyclic Chromophores with Intense Red-to-Near-Infrared Emission

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Neutral, globally aromatic boron-containing macrocycles are exceptionally rare, with the 10-bora-21,22,23,24-tetraoxacorroles reported herein representing only the second class of such compounds known to date, following the 5-bora-21,22-dioxaporphyrin we recently described, and are also the first neutral, globally aromatic boracorroles. Here, we present a furan-based 10-bora-21,22,23,24-tetraoxacorrole and an oxadiborepin-fused derivative thereof. The global aromaticity of both macrocyclic boranes in the neutral state is supported by experimental data and NICS and ACID cal­culations. They exhibit intense absorption spanning the ultraviolet to near-infrared (NIR) regions of the electromagnetic spectrum. Notably, the novel boracorroles display bright red and red-to-NIR fluorescence, achiev­ing quantum yields more than twice (Φ fl = 35–46%) that of conventional triphenylcorrole (Φ fl = 19%). DFT analysis reveals that the frontier orbital en­ergies are strongly modulated by the meso- B atom, generating a large HOMO to HOMO−1 energy gap and, consequently, mark­edly enhanced Q-band extinction coefficients arising from the predominantly single-configurational character of the S 0 →S 1 transition (HOMO to LUMO). Incorporation of the BOB bridge in the oxadiborepin-fused derivative significantly stabilizes the LUMO, giving rise to red-shifted absorption and emission alongside distinct electrochemical behavior. In addition, the BOB unit further amplifies the global aromaticity of the boracorrole, underscoring efficient π-conjugation across this heteroatomic bridge.

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