A Full‐Ring‐Fused Perylenediimide Dimer for High‐Performance n‐Type Organic Field‐Effect Transistors

Comprehensive Summary The design and synthesis of high‐mobility n‐type organic semiconductors remain a central research imperative in organic field‐effect transistor (OFET) technology. While π‐extended perylenediimides (PDIs) have been extensively investigated with tunable physicochemical properties, fully ring‐fused PDI derivatives remain underexplored—primarily hindered by synthetic challenges inherent to cyclizing electron‐deficient aromatic cores. Herein, we report f‐2PDI, a fully ring‐fused PDI dimer linked via a dithienothiophen‐pyrrolobenzothiadiazole (TPBT) bridge, which is obtained through Scholl cyclization mediated by ferric chloride in nitromethane. Unlike the electron‐rich thiophene‐benzene bridging motifs utilized in previous PDI dimers, TPBT's electron‐deficient fused backbone enhances electron affinity, synergizing with the electron‐accepting character of PDI moieties to fine‐tune frontier molecular orbital (FMO) energy levels and strengthen intermolecular electronic coupling. Comprehensive physicochemical characterization verifies low‐lying FMO energy levels, broadened absorption, a highly planar backbone conformation, and enhanced packing order with a favorable edge‐on orientation. These attributes translate to exceptional OFET electron mobility of 1.51 cm 2 ·V –1 ·s –1 —two orders of magnitude greater than that of its unfused analog s‐2PDI (0.012 cm 2 ·V –1 ·s –1 ). This striking mobility improvement underscores the effectiveness of full ring fusion in optimizing solid‐state charge transport, with particular emphasis on the utility of electron‐deficient bridging units for tailoring charge transport properties.