The first hexagonal columnar discotic liquid crystalline carbazole derivatives induced by noncovalent pi-pi interactions

The synthesis of 13 discotic mesogens is described in which the well-known hexakis( pentyloxy) triphenylene liquid crystalline material has been chemi cally modified to incorporate one, two, three and six carbazole moieties. T hese modifications have been achieved by the alkylation or esterification o f mono-, di-, tri- and hexa-hydroxytriphenylene derivatives with alkyl brom ides and carboxylic acids incorporating the carbazole moiety. The pure comp ounds are not liquid crystalline in nature but when doped with TNF, hexagon al columnar mesophases are induced, as shown by DSC, OPM and X-ray diffract ion. These mesophases exist below room temperature. The mesophase clearing temperatures are dependent on several factors including the chain length se parating the carbazole moiety from the triphenylene core, and the nature of the ether or ester linkage, and the degree of TNF doping. The data suggest that the most stable mesophases (highest clearing temperatures) are formed when a 2 : 1 complex is formed between the carbazole derivatives and the T NF, respectively. The correlation length obtained from X-ray diffraction re veals that the columnar order for one of the ether derivatives decreases, w hereas the correlation length increases for one of the ester derivatives. T his result suggests that the TNF is not only partaking in pi-pi noncovalent bonding interactions, but also in polar interactions with the C=O bond. Su ch mesogenic carbazole derivatives may have advantageous photorefractive pr operties over the amorphous polymeric materials.