COLUMNAR MESOPHASES OF OCTA-ALKYLOXYDIBENZOPYRENES AND THEIR CHARGE-TRANSFER COMPLEXES - SYNTHESIS, X-RAY AND NMR

The mesomorphic properties of five homologues of the 1,2,5,6,8,9,12,13 -octa-alkyloxydibenzopyrene series (DBPn, where n is the number of car bons in each of the side chains) and their charge transfer complexes w ith 2,4,7-trinitro-9-fluorenone (TNF) are described. The neat compound s exhibit a single mesophase which has been identified by X-ray diffra ctometry and optical microscopy as hexagonal columnar (D-hd). Two-dime nsional unit cell parameters are reported for the various homologues a s functions of temperature within the mesophase region. Deuterium NMR of labelled DBPn was used to determine the nature and rate of the mole cular reorientation in the mesophase. Addition of the electron accepto r TNF to the donor DBPn mesogens increases the stability range of the mesophases, with a maximum stability for the equimolar donor/acceptor mixtures. X-ray and deuterium NMR measurements on these charge transfe r stabilized mesophases are also reported. Besides being thermally mor e stable, they are more highly ordered and even exhibit well defined i ntramolecular stacking order, classifying them as D-ho. Under certain conditions, a diffraction peak at a position corresponding to twice th e normal intracolumnar distance is also observed, indicating that the donor and acceptor molecules are stacked alternately in the columns. W hen alkanes are added to the 1:1 charge transfer complexes, a lyotropi c nematic phase is induced. It is shown that these nematics are of the type N-c, with columnar structures as the mesogenic units.