Lateral Boron-Doping Intensifies Diradical State and Stabilizes Spins of peri-Acenoacene: A Nanographene Diradicaloid...

Control over topological structures is important for achieving desirable electronic structures of polycyclic aromatic hydrocarbons (PAHs). Especially the zigzag edge topology may induce spin-polarized edge states that are useful for spintronics and quantum devices but simultaneously enhances intrinsic instability in terms of oxidation activity and radical reactivity. In this study, we disclose lateral boron doping of peri-acenoacenes, a kind of fully zigzag-edged PAHs. The as-synthesized molecule features a planar C₄₄B₂ π-skeleton with two pairs of carbon- and boron-doped zigzag edges. It possesses a pronounced open-shell singlet diradical state, magnetic activity, and excellent ambient stability, characterized by its diradical character of 0.69 and singlet-triplet energy gap of -1.68 kcal mol^-1, together with a half-life time of 46 days, thus representing the first boron-doped nanographene diradicaloid. Moreover, a few unexpected physical properties were observed, such as a very narrow energy gap of <0.9 eV and long-wavelength NIR absorption beyond 1300 nm, as well as five-step reversible redox activity. As studied, the boron atoms make significant contributions to these intriguing properties via impeding π-electron current and stabilizing spins and π-orbitals through the characteristic vacant p orbital. In addition, theoretical calculations demonstrate that this lateral doping strategy is applicable to other heteroatoms including nitrogen, oxygen, and sulfur, and in comparison, the boron atom is not general but instead is unique.