Asymmetric conjugated oligomers based on polycyclic aromatics as high mobility semiconductors: The influence of chalcogens

We herein report the synthesis and characterization of four asymmetric conjugated oligomers based on polycyclic aromatics, i.e., 2-(5-hexylselenophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene (BTBT-S6), 2-(5-hexylfuryl- 2-yl)[1]benzothieno[3,2-b][1]benzothiophene (BTBT-F6), 2-(5-hexylselenophen-2-yl)[1]benzosele-nopheno[3,2-b][1]benzoselenophene (BSBS-S6) and 2-(5-hexylfuryl-2-yl)[1]benzofuro[3,2-b][1]benzofuran (BFBF-F6), for elucidating the influence of chalcogens on molecular geometries, electronic structures, thin film microstructures and the performance of organic thin-film transistors (OTFTs). Compared to the previously reported analogue 2-(5-hexylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene (BTBT-T6), all four molecules have higher-lying highest occupied molecular orbital (HOMO) energy levels. BTBT-S6 and BSBS-S6 (S replaced by Se atoms) display similar mesomorphic behavior and packing motif in solid state. However, BSBS-S6 shows much poorer crystallinity. Only crystal phase was observed for BTBT-F6 and BFBF-F6 (S replaced by O atoms). These two molecules also adopt the molecular arrangements, film growth modes and film morphology distinct from BTBT-S6 and BSBS-S6. Thus, the four molecules exhibited very different OTFT performance. BTBT-S6 showed the highest mobility of 4.68 cm(2)V(-1)s(-1) and all other three compounds exhibited mobilites lower than 1 cm(2)V(-1)s(-1).