Supramolecular liquid-crystalline networks built by self-assembly of multifunctional hydrogen-bonding molecules

Supramolecular liquid-crystalline networks have been prepared by self-assembly of multifunctional H-bond donor and acceptor molecules through the formation of intermolecular hydrogen bonds. Two tricarboxylic acids, 1,3,5-tras(2-(2-(4-carboxyphenoxy)ethoxy)ethoxy)-benzene (1) and 3,4-bis(2-(2-(4-carboxyphenoxy)ethoxy)ethoxy)benzoic acid (2), have been synthesized for the use as trifunctional H-bond donors. These trifunctional H-bond donors have been complexed with bifunctional H-bond acceptors, such as 4,4′-bipyridine (3), 1,2-bis(4-pyridyl)ethane (4), trans-1,2-bis(4-pyridyl)ethylene (5), and bis(2-(2-(4-(2-(4-pyridyl)-ethenyl)phenoxy)ethoxy)ethyl) ether (6), maintaining a 1:1 donor/acceptor group stoichiometry. All individual components are nonmesogenic. Self-assembly of these multifunctional compounds results in the formation of liquid-crystalline network structures. For example, the H-bonded complex 1/5 shows a smectic A phase from 176 to 156°C, while 2/5 exhibits a nematic phase between 200 and 87°C on cooling. This behavior is attributed to the dynamics of the hydrogen bonds. These results suggest that the trifunctional H-bond donors adopt linear conformations that induce calamitic mesomorphic behavior with bifunctional H-bond acceptors.