Molecular Design and Alignment for Ambipolar SCLC Mobility in Self-Assembled Columnar Discogens.

Abstract

The future of next-generation electronics relies on low-cost organic semiconductors that are tailored to simultaneously provide all requisite optoelectronic properties, focusing greatly on ambipolar charge-transport and solution processability. In this regard, room-temperature discotic liquid crystals (DLCs) are potential candidates, where quasi-1D self-assembly affords a charge-transport channel along their columnar axis. This work shows a molecular design strategy by utilizing anthraquinone as the primary motif, surrounded by ester functionalized tri-alkoxy phenyl units to develop room-temperature DLCs (1.1-1.3). Here, the polar ester functionality stabilizes the columnar mesophase over a wide range through the involvement of dipole-dipole interaction along with the π-π stacking. Throughout the entire mesophase transition, reported compounds 1.1-1.3 exhibit a highly ordered 2D columnar oblique (Col_ob) self-assembly. Space charge limited current (SCLC) experiments reveal balanced ambipolar charge transport, with the maximum hole and electron mobilities of 5.04 and 4.93 cm² V^-1 s^-1, respectively. From the conoscopic results, their propensity to align in a highly homeotropic fashion is demonstrated. It is further justified by the azimuthal plot corresponding to the (11) peak of grazing incidence small angle X-ray scattering (GISAXS), denoting the crucial role of the design and alignment for efficient movement of charge carriers in the material.