Room temperature mesogens formed by H-bonded Schiff-bases α,β,γ-triketonates

Three new series of Schiff bases 1a–c derived from α,β,γ-triketones 2a–c were synthesized and their mesomorphic properties investigated by polarizing optical microscope, differential scanning calorimetry, and powder X-ray diffraction. These Schiff bases were obtained by condensations of α,β,γ-triketones and 3-amino-1-propanol in refluxing absolute ethanol. All compounds were characterized and identified by 1H and 13C NMR spectroscopy. Both series of compounds 1a and 1c formed kinetically unstable monotropic behavior. Compounds 1a, 1c showed smectic A or/and C mesophases, in contrast compounds 1b exhibited rectangular columnar phases. The phases were confirmed by variable-temperature powder X-ray diffractions. The formation of mesophases in 1a–c was probably induced by intermolecular H-bonds, which was consistent with XRD data. Removal of –OH group in compound 1d led to the crystal phase. Some of these Schiff bases were in fact room temperature over a wide range of temperatures.