New discotic liquid crystals having a tricycloquinazoline core

Abstract

Tricycloquinazoline, a molecule of both biological and physical interest, has been found to function as the core fragment for a remarkable new family of discotic mesogens, which have C₃ symmetry and six aliphatic side chains. Eight representative homologous 2,3,7,8,12,13-hexa(thioalkoxy)tricycloquinazoline derivatives, 14, were synthesized, with alkyl side chain lengths varying from three to eighteen carbon atoms. These highly fluorescent, heteroaromatic compounds are conveniently obtained by nucleophilic substitution of hexachlorotricycloquinazoline, 3, by thiolate anions. Compound 3 is prepared by trimerization of 5,6-dichloroanthranil. 12. All compounds, 14 are mesogenic within a very broad temperature range. The nature of these new mesophases was studied by DSC, optical microscopy with polarized light, and X-ray diffraction. DSC measurements show highly reversible behaviour at the clearing point, indicating high chemical stability. Conversely, the melting transition was found to be irreversible. The diffraction spacings of three representative compounds (having 5,8, and 18 carbon atoms in the side chain) in the mesophase are consistent, in all cases, with a two dimensional hexagonal lattice having unit cell sides of α = 21·2, 24·8, and 34·7 Å, respectively and containing one molecule per unit cell.