Supramolecular transformation from ordered columnar to disordered columnar to tetragonal micellar structures in clicked dodeca-alkylated discotic triphenylene liquid crystals

Abstract

We prepared three discotic liquid crystals (DLCs) based on a triphenylene (TP) disc functionalized with twelve alkyl peripheries. The synthesis of the discogens was performed by a click reaction using Cu(OAc)₂ as the catalyst, with six triazolyl groups connecting the TP core with twelve alkyl chains. According to thermal data from differential scanning calorimetry (DSC), discogen 1, which has the shortest hexyl peripheries, exhibited two LC phases, and 2 and 3, with decyl and tetradecyl peripheries, respectively, displayed three LC phases as a function of the temperature. Structural analyses using small- and wide-angle X-ray scattering (SAXS and WAXS) techniques revealed ordered and disordered hexagonal columnar LC phases in all the discogens. On the other hand, an unconventional micellar phase with P4₂/mnm symmetry consisting of thirty micelles was found only in 2 and 3, when the temperature increased. The thermally induced transformation from the columnar to the micellar phase can be explained by increased chain entropy at higher temperatures. The complex micellar packing in the noncubic phase is attributed to the softness of the DLC micelles because the micellar corona consists of flexible alkyl chains. The discogen design concept in this study (i.e., the introduction of multibranched alkyl peripheries to the discotic mesogens via click chemistry) resulted in unconventional columnar-to-micellar transformation in conventional TP DLCs.