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 (y0=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−1 from SQUID measurements). Its electronic properties are compared with previously reported peri‐tetracene and teranthene derivatives. A stable derivative of [4,3]peri‐acene with three rows of peri‐fused tetracenes was isolated in crystalline form. It exhibits a unique structure with eight localized Clar's sextets and shows a large diradical character (94.8 %) as well as a small singlet–triplet energy gap (−0.57 kcal mol−1).