Abstract

Two series of hexakis(alkyloxy)triphenylenes have been synthesised and characterised. All materials contain two different lengths of n-alkyloxy chains. Series I (C₅C_n) materials contain three –OC₅H₁₁ chains and three –OC_nH_2n + 1 chains. Series II (C_mC_n) materials contain three –OC_mH_2m + 1 chains and three –OC_nH_2n + 1 chains, such that m + n  = 10. Hexagonal columnar mesophases are observed in Series I for n ≥ 3 and, in Series II, for C₅C₅ and C₆C₄. Investigation by XRD shows that, within Series I, increasing the C_n chain length increases the intercolumnar spacing. Furthermore, the intercolumnar spacings for constitutional isomers are identical. The difference in the lengths of the two types of alkyl chain at the periphery of the molecules is defined as the Interdigitation Length (IL) and is a measure of the maximum extent of interdigitation that is possible between neighbouring molecules. Series I and II materials have been studied to probe the effect of IL on the change in enthalpy (ΔH_Col–I) and entropy (ΔS_Col–I) for the mesophase to isotropic liquid phase transition. In contrast to C_xC_x materials, which show a decrease in ΔH_Col–I and ΔS_Col–I with increasing chain length, Series I and II mesogens all exhibit ΔH_Col–I and ΔS_Col–I values similar to those of long chain C_xC_x materials, irrespective of chain length.