Synthesis of Mixed Tail Triphenylene Discotic Liquid Crystals: Molecular Symmetry and Oxygen-Atom Effect on the Stabilization of Columnar Mesophases

A series of propyloxyacetyloxy- and alkoxy-containing mixed tail triphenylene based discotic liquid crystals, abbreviated as TP(OCnH2n+1)3(OCOCH2OC3H7)3, n = 4 ~ 8, and hexa(propyloxyacetyloxy)triphenylene, TP(OCOCH2OPr)6 have been synthesized and their liquid crystalline properties have been investigated through differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). These mixed tail triphenylene derivatives exhibit much more stable hexagonal columnar mesophases (Colh) and much wider mesophase temperature ranges than their hexaalkoxytriphenylene TP(OR)6 and hexaalkanoyloxytriphenylene TP(OCOR’)6 analogues. The asymmetrical compounds 2,6,11-trialkoxy-3,7,10-tri(2-propyloxyacetyloxy)triphenylenes with n = 5 ~ 8 possess higher clearing points and wider mesophase ranges than their symmetrical isomers 2,6,10-trialkoxy-3,7,11-tri(2-propyloxyacetyloxy)triphenylenes.