Electron-deficient acene-based liquid crystals: Dialkoxydicyanopyrazinoquinoxalines

Three electron-accepting dialkoxydicyanopyrazinoquinoxaline derivatives (1a, 1b, and 1c) showed properties of smectic (Sm) liquid crystals. Temperature-dependent X-ray diffraction studies were consistent with the formation of a bilayer structure through the π-overlap and interdigitation of alkoxy chains in the Sm liquid crystalline state. Intermolecular dipole-dipole interactions between the cyano groups played an important role in stabilizing the bilayer structure and liquid crystalline properties. Elongation of the alkoxy chains from C₆H₁₃O- (1a) and/or C₁₂H₂₅O- (1b) to C₁₈H₃₇O- (1c) changed the molecular arrangements and the liquid crystal phase from SmA to SmC, suggesting the importance of the van der Waals interaction of C_nH_2n+1O- chains for stabilizing the liquid crystalline phase. A hole-mobility value of 5 × 10^-3 cm² V^-1 s^-1 was observed for the SmA phase of 1b at 438 K based on transient photocurrent measurements.