Synthesis of a novel smectic liquid crystalline glass and characterization of its charge carrier transport properties

Abstract

A new organic semiconductor material with both a self-organized molecular alignment in smectic liquid crystals and a solid nature in amorphous materials, i.e., a glassy liquid crystalline organic semiconductor has been proposed, and its model compound, 1,3,5-benzenetricarboxylic acid, tris{12-[6′-(4′′-octylphenyl)-2′-naphthyloxy]-1-dodecyl ester} (LCG-triester 8-PNP-O12), was synthesized, and we characterized its phase transition behaviors in slow cooling and rapid cooling. It exhibited smectic A (SmA) and smectic B (SmBhex) phases in slow cooling, and a SmBhex glassy phase with a high Tg close to 60 °C when cooled rapidly from the SmA and SmBhex phases. Its charge carrier transport properties in the smectic mesophases, including the liquid crystal glassy phase, were first studied by the time-of-flight (TOF) technique, which revealed that the hole mobility in the SmBhex glassy phase was about 3.5 × 10−4 cm2 v−1s−1, comparable to that in the SmBhex liquid crystal phase. We concluded that the high charge transport properties of the smectic mesophase are successfully maintained in the solid glassy state.