Solution-Processable Quinoidal Dithioalkylterthiophene-Based Small Molecules Pseudo-Pentathienoacenes an Intramolecular S···S Lock for High-Performance n-Type Organic Field-Effect Transistors.

A new organic small-molecule family comprising tetracyanoquinodimethane-substituted quinoidal dithioalky(SR)terthiophenes (s) ( (); SR = SCH, (); SR = SCH, (); SR = SCH) was synthesized and contrasted with a nonthioalkylated analogue ( (); R = CH). The physical, electrochemical, and electrical properties of these new compounds are thoroughly investigated. Optimized geometries obtained from density functional theory calculations and single-crystal X-ray diffraction reveal the planarity of the SR-containing core. s pack in a slipped π-π stacked two-dimensional arrangement, with a short intermolecular stacking distance of 3.55 Å and short intermolecular S···N contacts of 3.56 Å. Thin-film morphological analysis by grazing incident X-ray diffraction reveals that all molecules are packed in an edge-on fashion on the substrate. The favorable molecular packing, the high core planarity, and very low lowest unoccupied molecular orbital (LUMO) energy level (-4.2 eV) suggest that s could be electron-transporting semiconductors. Organic field-effect transistors based on solution-sheared exhibit the highest electron mobility of 0.77 cm V s with good ambient stability, which is the highest value reported to date for such a solution process terthiophene-based small molecular semiconductor. These results demonstrate that the device performance of solution-sheared s can be improved by side chain engineering.