Novel High-Performance Liquid-Crystalline Organic Semiconductors for Thin-Film Transistors

A novel class of liquid-crystalline organic semiconductors based on 2,5′-bis-[2-(4-pentylphenyl)vinyl]-thieno(3,2-b)thiophene and 2,5′-bis-[2-(4-pentylphenyl)vinyl]-(2,2′)bithiophene were synthesized through proper structural design. The materials exhibited high field-effect mobilities up to 0.15 cm2 V−1 s−1 and current on/off ratio of 1 × 106. The high performance is attributed to their abilities to form highly ordered structures through molecular packing, which is revealed by single-crystal and thin film X-ray diffraction (XRD). The structures were analyzed by polarized optical microscope and showed obvious changes in texture corresponding to the phase changes in DSC diagrams, indicating their abilities to form liquid-crystalline structures. High environmental stabilities have been demonstrated with these new compounds, which is consistent with their low HOMO levels and large band gaps. In addition, UV−vis spectra of the thin films formed from these compounds have showed that their absorption peaks mainly appear in the range of ultraviolet spectrum region, indicating they could be used for the application of those circuits requiring transparency such as optoelectronic devices.