Highly Contorted 1,2,5-Thiadiazole-Fused Aromatics for Solution-Processed Field-Effect Transistors: Synthesis and Properties

A straightforward strategy has been used to construct 1,2,5-thiadiazole-fused 12-ring π systems through twofold Stille coupling and subsequent cyclodehydrogenation by utilizing the building blocks of naphthodithiophene and 5,6-substituted benzo[b]-2,1,3-thiadidazole. Molecules 1 a and 1 b, which exhibit highly contorted π surfaces, show a butterfly-shaped conformation according to DFT calculations. Within the molecules, a plane-to-plane angle of 44.8° was found. UV/Vis absorption, thermogravimetric analysis, differential scanning calorimetry, and cyclic voltammetry (CV) were used to study their physical properties. Strong intermolecular interactions of the nonplanar molecules were also observed by concentration-dependent ¹H NMR spectroscopy measurements and thin-film XRD characterization. The low-lying LUMO and high-lying HOMO levels of the molecules are −3.73 and −5.48 eV, respectively, as estimated from CV measurements; this indicates their potential as semiconducting materials for solution-processed organic field-effect transistors (OFETS). A field-effect hole mobility of up to 0.035 cm² V⁻¹ s⁻¹, a threshold voltage of 6.98 V, and a current on/off ratio of 8.65×10⁵ in air for 1 a have been demonstrated with the top-contact bottom-gate field-effect transistor device structures; this represents an important step toward the solution-processed OFET application of contorted aromatics.