Fused-ring and linking group effects of proton donors and accepters on simple H-bonded liquid crystals

Two fused-ring structures, 6-decyloxy-2-naphthoic acid C(10)ONA (3) and 6-dodecyloxy-isoquinoline IS (8), were synthesized and utilized as proton donor and acceptor moieties to construct a series of simple mesogenic supramolecules. The other complementary hydrogen-bonded (H-bonded) moieties are benzoic acids, thiophenecarboxylic acid and pyridines containing different alkyl chain lengths connected by ether and ester linkages, i.e. 4-alkoxybenzoic acid C(n)OBA (1), terephthalic acid monoalkyl ester C(n)COOBA (2), 2,5-thiophenedicarboxylic acid monodecyl ester C(10)COOTHA (4), 4-alkoxypyridine CnOP (6) and isonicotinic acid alkyl ester CnCOOP (7). Several series of simple mesogenic supramolecular dimers were constructed from 1:1 molar ratios of proton donors (C(n)OBA, C(n)COOBA, C(10)ONA and C(10)COOTHA) and proton accepters (IS, CnOP and CnCOOP), though the proton acceptor CnCOOP induced phase separation in all complexes. In order to investigate their fused-ring and linking group effects on the mesogenic properties of the H-bonded complexes, analogous simple supramolecular structures are compared. Supramolecular architecture and the distinct mesomorphism of these simple H-bonded liquid crystalline materials were confirmed by polarizing optical microscopy, DSC and powder X-ray diffraction experiments.