Soluble star-shaped molecules based on thiophene derivatives as organic semiconductors for field-effect transistor applications

New star-shaped crystalline molecules have been synthesized through Horner-Emmons reactions using hexyl-substituted thiophene-based carbaldehydes as dendrons and [1,2,4,5-tetra-(diethoxy-phosphorylmethyl)-benzyl]-phosphonic acid diethyl ester as the core units; these molecules have been fully characterized. Three thiophene-based star-shaped molecules exhibit good solubility in common organic solvents and good self-film-forming properties. They are intrinsically crystalline as they exhibit well-defined X-ray diffraction patterns from uniform and preferred orientations of molecules. The semiconducting properties of the star-shaped molecules have been evaluated in organic field-effect transistors. Three crystalline conjugated molecules, 4, 8, and 12, exhibit carrier mobilities as high as 6.0 (±0.5) × 10^-3, 2.5 (±0.5) × 10^-4, and 2.5 (±0.5) × 10^-2 cm ²·V^-1·s^-1, respectively. The dithienothiophene dendrons in 12 induce easy crystallization and small crystallite formation even in as-cast films and can be found to densely cover the surface of a dielectric layer. This helps in attaining good network interconnection of the carrier transport channel, which is responsible for the relatively high carrier mobility in solution-processed organic semiconductors for OFET.