Microwave-assisted facile synthesis of liquid crystalline non-symmetrical hexaalkoxytriphenylenes containing a branched chain and their characterization

Two novel series of liquid crystalline non-symmetrical hexaalkoxytriphenylenes containing a branched alkyl chain have been prepared using microwave dielectric heating. Series 1 contains 2-ethyl hexyloxy group as the branched chain whereas series 2 contains 3,7-dimethyl octyloxy as the branched chain along with five normal alkoxy chains. The number of carbon atoms varies from four to eight in the normal alkoxy chains. Mesophase behaviour of the compounds has been characterized by polarizing optical microscopy, differential scanning calorimetry and mesophase structure has been characterized by X-ray diffractometry. All the compounds show enantiotropic mesophase transitions with columnar hexagonal structure. In series 1 (4a-e) the mesophase range and transition temperatures of all the compounds are lowered as compared to the parent compounds whereas in series 2 (5a-e) the transition temperatures of all the compounds are lowered, mesophase range for lower members are decreased, however, higher members show more mesophase stability. Both melting and clearing temperatures of series 2 (5a-e) show strong odd-even effect. The intercolumnar distance increases as expected for compounds of both the series with increase in alkyl chain length with some degree of interdigitation of the alkyl chains. The intercolumnar distances for the compounds of the series 2 are slightly higher than the compounds of the series 1. Compound 4c displays homeotropic alignment without using any special technique for alignment of the columnar phase or application of any external force.