Induction of a cholesteric phase via self-assembly in supramolecular networks built of non-mesomorphic molecular components

Abstract

Supramolecular hydrogen-bonded networks have been prepared by self-assembly of a chiral bifunctional H-bond acceptor and achiral trifunctional H-bond donors. A stilbazole dimer, (R)-1,2-bis{4-\\[2-(4-pyridyl)ethenyl]phenoxy}propane (1) has been synthesized for use as a chiral component for cholesteric networks. Compound 1 has been complexed with tri functional H-bond donors, p,q-bis{2-\\[2-(4-carboxyphenoxy)ethoxy]ethoxy}benzoic(2-6) \\[p, q =2,4 (2); 2,5 (3); 2,6 (4); 3,4 (5); 3,5 (6)], maintaining the 1 :1 donor/acceptor group stoichiometry. With the exception of the complex from 1 and 6, these H-bonded complexes exhibit cholesteric phases and glass transition behaviour, while all individual components are non-mesomorphic. For example, the H-bonded complex consisting of 1 and 2 shows a cholesteric phase from 75 to 184 C on heating. These results suggest that supramolecular liquid crystalline networks with macroscopic helical structures have been formed by intermolecular hydrogen bonds between non-mesomorphic smaller molecules. The solid state films obtained by cooling the samples from their mesophases exhibit cholesteric colours associated with selective reflection. The cholesteric structure is preserved in the glassy state of the networks.