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.