A Stable [4,3]Peri-acene Diradicaloid: Synthesis, Structure, and Electronic Properties.

The synthesis of peri-fused acenes (peri-acenes) with two or more rows is challenging due to their intrinsic open-shell diradical character. Herein, we report the isolation of a derivative (4) of [4,3]peri-acene in crystalline form. The parent [4,3]peri-acene, containing three rows of tetracene, has a large diradical character (y =94.8 %) originating from aromatic stabilization. Due to kinetic blocking, 4 showed a reasonable stability with a half-life time of ≈157 h under ambient conditions. Its structure was determined by X-ray crystallographic analysis, and bond-length analysis revealed eight localized Clar's sextets. 4 exhibited an open-shell singlet ground state with a narrow electrochemical energy gap (1.13 eV) and a small singlet-triplet energy gap (-0.57 kcal mol from SQUID measurements). Its electronic properties are compared with previously reported peri-tetracene and teranthene derivatives.