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Novel hexyl-substituted bisthiophene compounds containing a thiazolothiazole(5,4-d) unit have been explored. The molecules are soluble in common organic solvents, which would enhance their chance of possible integration in printable electronics. Synthesis and complete elucidation of the chemical structures by detailed 1D/2D NMR spectroscopy are described. This provides interesting input for chemical shift prediction software, because few experimental data on this type of compounds are available. Furthermore, the potential n-type character of these derivatives is verified using electrochemical measurements. In addition, the low-bandgap character of conjugated polymers containing the thiazolothiazole unit is demonstrated by performing an electropolymerization.

A series of 5′‐aryl‐substituted 2,5‐bis(3′‐hexylthiophen‐2′‐yl)thiazolo[5,4‐d]thiazole derivatives was synthesized and these expanded semiconductors were investigated as active materials for solution‐processable organic field‐effect transistors. Field‐effect mobilities of up to 10−3 cm2 V−1 s−1 were obtained, representing the first reasonable FET behavior for highly soluble thiazolo[5,4‐d]thiazole‐based small organic compounds suitable for printable electronics. Thermal and electrooptical material properties were studied by thermogravimetric analysis, differential scanning calorimetry, cyclic voltammetry, and UV/Vis spectroscopy. Trends in thermal and optical data were supported by (time‐dependent) density functional theory calculations. Additional X‐ray diffraction, atomic force microscopy, and scanning electron microscopy studies provided insight in the relationship between the molecular structures, film morphologies, and FET performances. The fibrillar microcrystalline structure observed for the best‐performing thienyl‐substituted material was linked to the high mobility.