Room-temperature columnar liquid crystalline organic semiconductors based on pyrazino[2,3-<i>g</i>]quinoxaline: synthesis, characterization, sensing and hole mobility studies.

Abstract

We have synthesized three molecules based on the pyrazino[2,3-<i>g</i>]quinoxaline core, where each structure possesses pendant phenyl rings linked to terminal alkoxy substituents <i>via</i> a phenyl acetate group. The molecules are differentiated by the number of alkoxy chains present at their ends. Photophysical studies of the derivatives revealed high molar extinction coefficients and substantial Stokes shifts. They exhibited good thermal stability. The compound with three peripheral alkyl chains on each side of the symmetrical molecule PQE1 stabilizes the columnar hexagonal mesophase, but PQE2 and PQE3, with two chains per side (<i>meta</i>- or <i>ortho</i>-<i>meta</i>-positioned), exhibited crystalline phases. This emphasizes the role of alkoxy chain number and positioning in promoting mesophase formation in structurally similar derivatives. Cyclic voltammetry revealed comparable redox behavior of the derivatives. Experimental and theoretical analyses showed that they have similar band gaps. PQE1 has demonstrated hopping-assisted charge transport, exhibiting hole mobility in the order of 10^-4 cm² V^-1 s^-1 along with specific photoresponsive behavior to 450 nm light. These findings elucidate structure-mesophase relationships, guiding the design of liquid crystalline materials with tailored optoelectronic properties.