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-tris(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.