Luminescent lanthanides complexes with mesogenic pyridone ligands: Emission and liquid crystals properties

Abstract

In this work, a systematic investigation of the influence of N-alkylated 4-pyridone ligands containing one cyanobiphenyl mesogenic group linked via a spacer with variable length (6, 8, 9 or 10 methylene groups) on the liquid crystalline properties and luminescence properties of the resulting lanthanide complexes with Eu(III), Sm(III) and Tb(III). The chemical structures of the new products were determined by 1H and 13C NMR spectroscopy, as well as elemental analysis and IR spectroscopy. The lanthanide ions are 9-coordinate and surrounded by three pyridone ligands and three bidentate nitrate ions. The thermal behavior of the new products was analyzed by differential scanning calorimetry (DSC) and thermogravimetrical analysis (TG). The nature of the liquid crystalline phase was confirmed by polarizing optical microscopy (POM) and powder X-ray diffraction (XRD) studies. All complexes remain in the glassy state at room temperature while at higher temperature these materials display a SmA phase. Higher clearing temperatures were recorded for longer spacers. The emission spectra show characteristic emission bands for each lanthanide ion. The emission of the new complexes measured as a function of temperature decreases noticeably upon the increase of temperature and this process is reversible on cooling.