Solution-Processable Organic Semiconductors Featuring S-Shaped Dinaphthothienothiophene (S-DNTT): Effects of Alkyl Chain Length on Self-Organization and Carrier Transport Properties

A series of dialkylated dinaphtho[2,1-b:2′,1′-f]thieno[3,2-b]thiophenes (S-DNTTs) featuring an S-shaped sinuous π-core substituted with different alkyl chains were developed as versatile p-type organic semiconductors. The effects of the crooked shape of the π-core and the length of the flexible alkyl chains on the solution processability, thermal durability, self-organization ability, and charge-transport functionality were systematically investigated. Because the newly developed dialkylated S-DNTTs show relatively high solubilities in organic solvents, high-performing organic field-effect transistors (OFETs) can be fabricated using both dip-coating and vacuum-deposition techniques. It was revealed that the OFET performance for dialkylated S-DNTTs was significantly affected by subtle variations in the alkyl chain length. Consequently, among this family, S-DNTT-10 with longer decyl groups achieved the highest field-effect hole mobilities of up to 11 and 3.5 cm2 V-1 s-1 with on/off current ratios of over 107 in the dip-coated and vacuum-deposited OFETs, respectively. In addition, the high OFET performance of the S-DNTT-10-based system can be preserved for more than three months under ambient conditions, demonstrating its long-term stability and high durability. As revealed by two-dimensional grazing incidence X-ray diffraction analyses, a simple dip-coating method can induce unidirectional molecular orientation/assembly and thereby produce highly oriented single-crystalline domains, leading to such high hole mobilities exceeding 10 cm2 V-1 s-1 in the dip-coated OFETs.