Competition and promotion of different mesophases in a series of novel unsymmetrical discotic dimers via subtle modification of spacers and peripheral side chains

The highly ordered columnar plastic (Col(hp)) phase with charge carrier mobility up to 10(-2) cm(2) v(-1) s(-1) which is comparable to that of organic single crystals is considered as a potential charge transport material applied in electronic devices. The Colhp phase formed by monomers hexapropoxytriphenylene (HAT3) and hexabutoxytriphenylene (HAT4) as well as their corresponding symmetrical dimers can be supercooled into glassy states but with no monodomains obtained. It is expected that longer-lasting glassy states with monodomains can be engineered by making them subtly unsymmetrical. Unsymmetrical dimers with a Colhp phase can be constructed by the combination of any two of the three different monomers (HAT3, HAT4 and HAT5). Herein, three series of triphenylene-based dimers T3,4Dm, T4,5Dm, and T3,5Dm were synthesized by changing the spacer length (m = 6-12) and their mesophase was investigated by differential scanning calorimetry, polarizing optical microscopy, and wide-angle X-ray diffraction. These dimers can not only retain the order of the corresponding monomers but also obtain highly ordered single domains much more easily. To our surprise, the superlattice structure was firstly observed among these unsymmetrical dimers which made them not only be tractable models for discotic polymers with charge carrier mobility up to 10(-2) cm(2) v(-1)s(-1) but also provide a practical way for cultivating single crystals from discotic liquid crystals. The molecular stacking suggested that two different subunits tend to self-recognize and stack together, which was firstly reported by us and is very meaningful for supramolecular self-organization.