Hepta-thienoacenes with Internal Carbazole: Synthesis, Regioselectivities and Organic Field-Effect Transistor Applications

Acenes/heteroacenes, the most widely studied small-molecule organic semiconductors, always possess linear structures. In this work, three stable, soluble and angular π-extended hepta-thienoacenes with an internal carbazole, that is, thienobenzo-fused carbazole (DTBCz) were synthesized via a four-step tandem method. The tandem synthesis starting from carbazole derivatives led to interesting isomeric effects. The synthetic regioselectivity was discussed in detail. Their physical properties and electron density distributions were studied by UV/Vis absorption, photoluminescence, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), cyclic voltammetry (CV) measurements, and theoretical calculations. Their potentials as semiconducting materials were evaluated by fabricating the solution-processed organic field-effect transistors (OFETs). The more angular shaped isomer of DTB[32,34]Cz displayed the best performance with hole mobility up to 0.0044 cm² V⁻¹ s⁻¹ in devices with a thickness of ca. 115 nm. Particularly, the performance of DTB[32,34]Cz-based devices showed less dependence on the thickness of their active layer.