Novel electron-deficient phenanthridine based discotic liquid crystals

Abstract

Nitrogen-containing polycyclic core 5-phenylnaphtho[1,2,3,4-lmn] phenanthridine and its nitro-functionalized positional isomers were synthesized using Pictet-Spengler reaction between hexaalkoxytriphenylene-1-amine and various aryl aldehydes. The hexagonal columnar phase was observed in all the synthesized novel compounds. Mesomorphic characterization was carried out using conventional thermal analysis and X-ray diffraction techniques. These compounds showed room temperature liquid crystal phase and there is no crystalline phase observed even at −20 °C upon cooling from the isotropic temperature. Further, the long range of mesophase was confirmed by polarizing optical microscopy. Subsequently, charge transfer complexes were prepared by mixing the synthesized polycyclic hetero-aromatic compounds with 2,3,6,7,10,11-hexakis(octyloxy)-triphenylene. In UV–Vis absorption spectra, a redshift was found for the charge transfer complexes; which confirmed the interaction between donor-acceptor counterparts. The electrical conductivity of the charge transfer complexes and their pure target compounds was measured.