Polarized emission and dielectric studies of novel lanthanidomesogens based on 4-pyridone ligands

Abstract

Novel lanthanidomesogens based on lanthanide nitrates carrying three 4-pyridone ligands having two alkoxy chains at the periphery were synthesized and their structure was assigned based on IR spectroscopy and elemental analysis. Their thermal stability was evaluated by TG analysis confirming that the decomposition starts at very high temperatures around 300°C. The liquid crystalline properties were investigated by using a combination of techniques: polarized optical microscopy (POM) and differential scanning calorimetry (DSC) and, for selected compounds, by variable-temperature powder X-ray diffraction. The new liquid crystal display a hexagonal columnar phase (Colh) between 63°C and 242°C, depending on the length of the alkyl chain. Dielectric spectroscopy on a wide frequency range was used to evaluate the dipolar relaxation processes. The emission properties of a mixture of E7 doped with a selected europium complex filled in a planar cell were investigated on changing the applied voltage, ranging from 0V up to 15V.