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Self-assembled liquid crystals formed by hydrogen bonding between non-mesogenic 1,3,4-oxadiazole-based pyridines and substituted benzoic acids

A series of new supramolecular liquid crystalline complexes have been prepared readily through intermolecular hydrogen bonding between non-mesogenic 1,3,4-oxadiazole-based pyridines and substituted benzoic acids. The liquid crystalline properties of the H-bonded complexes were studied by infrared spectrometry, polarising optical microscopy, differential scanning calorimetry and small-angle X-ray scattering. All the H-bonded complexes exhibited liquid crystalline behaviours with various mesophases such as nematic (N), smectic A and hexagonal columnar mesophases, which are determined by the electronic nature of terminal groups and the number of alkoxy chains of the H-acceptors and H-donors. The rod-like H-bonded complexes 2a/3a, 2a/3b and 2a/3c with an electron-withdrawing end group (NO2, F or CN) fascinate to form an enantiotropic smectic A phase, whereas complex 2a/3d bearing an electron-donating methoxy end group tends to display a monotropic N phase. In contrast, the disc-shaped complexes 2b/3e and 2c/3e with six peripheral decyloxy chains are room temperature liquid crystals exhibiting columnar mesophase. All the complexes 2a/3a, 2a/3b, 2a/3c and 2a/3d in CH2Cl2 solutions exhibited an intense broad absorption peak at ca. 303 nm, and emitted a strong blue emission with λmax at ca. 390 nm and good photoluminescence quantum yields (ΦFL = 0.56–0.81).