Solution-Processable Dithienothiophenoquinoid (DTTQ) Structures for Ambient-Stable n-Channel Organic Field Effect Transistors

A series of dialkylated dithienothiophenoquinoids (DTTQs), end-functionalized with dicyanomethylene units and substituted with different alkyl chains, are synthesized and characterized. Facile one-pot synthesis of the dialkylated DTT core is achieved, which enables the efficient realization of DTTQs as n-type active semiconductors for solution-processable organic field effect transistors (OFETs). The molecular structure of hexyl substituted DTTQ-6 is determined via single-crystal X-ray diffraction, revealing DTTQ is a very planar core. The DTTQ cores form a “zig-zag” linking layer and the layers stack in a “face-to-face” arrangement. The very planar core structure, short core stacking distance (3.30 Å), short intermolecular SN distance (2.84 Å), and very low lying lowest unoccupied molecular orbital energy level of −4.2 eV suggest that DTTQs should be excellent electron transport candidates. The physical and electrochemical properties as well as OFETs performance and thin film morphologies of these new DTTQs are systematically studied. Using a solution-shearing method, DTTQ-11 exhibits n-channel transport with the highest mobility of up to 0.45 cm² V⁻¹ s⁻¹ and a current ON/OFF ratio (I_ON/I_OFF) greater than 10⁵. As such, DTTQ-11 has the highest electron mobility of any DTT-based small molecule semiconductors yet discovered combined with excellent ambient stability. Within this family, carrier mobility magnitudes are correlated with the alkyl chain length of the side chain substituents of DTTQs.