Synthesis and self-assembly of donor-spacer-acceptor molecules. Liquid crystals formed by single-component "complexes" via intermolecular hydrogen-bonding interaction

A series of donor-spacer-acceptor molecules, 4-{[n-(4-stilbazoyl)] alkyloxy}benzoic acid, where n is the number of carbon atoms in alkyloxy chain and equals to 6, 8, 10, and 12, respectively, for 6a-d, were synthesized. The molecular "complexes" formed by identical 6a-d molecules generated hydrogen-bonded liquid-crystalline polymers by connecting a rigid donor and a rigid acceptor of the molecules via hydrogen-bonding interaction. The thermal behaviors were studied by differential scanning calorimetry, polarizing microscopy and X-ray diffraction. The phase transition temperature of 6a-d on both cooling and heating decreased steadily with the increase in length of the spacer. The hydrogen-bonding interaction in 6a-d was investigated by X-ray photoelectron spectroscopy and FT-IR spectroscopy. The intermolecular hydrogen-bonding interaction was evidenced by the fact that there were two characteristic bands at 2450 and 1920 cm(-1) in the FT-IR spectra and the change in binding energy of N 1s by 0.72-0.88 eV relative to its reference compound trans-4-octyloxy-4'-stilbazole (7) were observed.