Organic semiconductor materials are interesting due to their application in various organic electronics devices. [1]benzothieno[3,2-b][1]benzothiophene (BTBT) is a widely used building block for the creation of such materials. In this work, three novel solution-processable regioisomeric derivatives of BTBT—2,7-bis(3-octylthiophene-2-yl)BTBT (1), 2,7-bis(4-octylthiophene-2-yl)BTBT (2), and 2,7-bis(5-octylthiophene-2-yl)BTBT (3)—were synthesized and investigated. Their optoelectronic properties were characterized experimentally by ultraviolet–visible and fluorescence spectroscopy, time-resolved fluorimetry, and cyclic voltammetry and studied theoretically by Time-Dependent Density Functional Theory calculations. Their thermal properties were investigated by a thermogravimetric analysis, differential scanning calorimetry, polarizing optical microscopy, and in situ small-/wide-angle X-ray scattering measurements. It was shown that the introduction of alkyl substituents at different positions (3, 4, or 5) of thiophene moieties attached to a BTBT fragment significantly influences the optoelectronic properties, thermal stability, and phase behavior of the materials. Thin films of each compound were obtained by drop-casting, spin-coating and doctor blade techniques and used as active layers for organic field-effect transistors. All the OFETs exhibited p-channel characteristics under ambient conditions, while compound 3 showed the best electrical performance with a charge carrier mobility up to 1.1 cm²·V⁻¹s⁻¹ and current on/off ratio above 10⁷.

Derivatives of naphthalene-diimide (NDI) are among the most studied and popular organic semiconductors showing n-type conductivity. However, the structure and optoelectronic properties of crystalline NDIs N-functionalized with conjugated donors have not been investigated yet. In this study, a novel donor–acceptor compound NDI-Stb bearing one NDI core, as an acceptor, and two stilbene moieties covalently linked via imide positions of NDI, as a donor, was synthesized. A combined experimental and theoretical approach was applied to study the structure and properties of NDI-Stb molecules and its crystals. We found and explained why optical absorption and high-frequency Raman spectra are inherited from those of donor and acceptor moieties, but photoluminescence is determined by the properties of the whole molecule. We resolved the structure of NDI-Stb single crystals and found that strong intermolecular interactions operate along two directions, for which NDI cores stack either on similar cores or on stilbene moieties. These interactions cause suppression of dynamic disorder indicated by a weak low-frequency Raman signal and solid-state luminescence enhancement. Ambipolar charge transport was predicted, and electron transport was experimentally observed in NDI-Stb polycrystalline thin films. The results obtained highlight the potential of using NDIs N-functionalized with conjugated donor moieties in optoelectronic applications, and improve the understanding of structure–property relationships necessary for the rational design of novel donor–acceptor organic semiconductors.