HEXAALKOXYTRICYCLOQUINAZOLINES - NEW DISCOTIC LIQUID-CRYSTALS

Tricycloquinazoline (TCQ), a molecule of both biological and physical interest, has been found to function as the core fragment for a new fa mily of discotic mesogens, which have C3 symmetry and six aliphatic si de chains. Six representative homologous 2,3,7,8,12,13-hexaalkoxy-TCQ derivatives 5 were synthesized, with alkyl side chain lengths varying from 3 to 16 carbon atoms. These highly fluorescent, heteroaromatic co mpounds are conveniently obtained by alkylation of hexahydroxy-TCQ, 10 . The latter is prepared by trimerization of 5,6-dimethoxyanthranil, 8 , followed by demethylation of the resultant hexamethoxy-TCQ, 9. All c ompounds, 5, are mesogenic within a very broad temperature range. The nature of these new mesophases was studied by DSC and by optical micro scopy with polarized light and X-ray diffraction. DSC measurements sho w highly reversible behavior at both melting and clearing points, indi cating high chemical stability. Photomicroscopic pictures show mosaic textures, characteristic of an ordered hexagonal, columnar phase (D(ho )), that are very similar to those we reported earlier for hexakis(thi oalkoxy)-TCQ derivatives 4. The diffraction spacings of two representa tive compounds (having 5 and 11 carbon atoms in the side chain) in the mesophase are consistent with a two-dimensional hexagonal lattice hav ing unit cell sides of a = 21.2 and 28.7 angstrom, respectively, and c ontaining one molecule per unit cell.