Discotic liquid crystalline hexabenzocoronenes carrying chiral and racemic branched alkyl chains: Supramolecular engineering and improved synthetic methods

Article abstract of DOI:10.1016/S0040-4020(01)00252-6

In this paper we present the synthesis and characterization of three different thermotropic liquid crystalline derivatives of hexabenzocoronene (HBC), substituted at the periphery by six chiral or racemic branched (3,7-dimethyloctanyl) chains, namely the chiral 5a, racemic 5b, and mono-bromo functionalized 18 carrying five alkyl chains. Improved methods for synthesis of HBC precursors, largely relying on transition-metal catalyzed coupling reactions, are also described. Solubility and processability are increased while the thermal K→D_H transitions are shifted to lower temperatures, relative to analogous HBCs carrying n-alkyl chains. In case of substitution with a chiral branched alkyl chain, 5a, strong signals have been recorded by means of circular dichroism spectroscopy. All new compounds were characterized by ¹H, ¹³C NMR, and UV-Vis spectroscopy, and FD-MS. Preliminary mesophase characterization is carried out by differential scanning calorimetry (DSC) and polarized light microscopy. In the course of the DSC experiments, optically pure and racemic HBC derivatives were compared.