Articles

A new class of thermotropic lanthanido mesogens has been designed and prepared. They are based on 4-pyridone ligands that possess mesogenic cyanobiphenyl groups attached to the 4-pyridone unit via a flexible long alkyl spacer and show a very high thermal stability (decomposition temperatures near 300 °C). Depending on the alkyl length spacer, these complexes exhibit a SmA phase with transition temperatures influenced by the number of mesogenic groups employed and the spacer length.

A series of novel liquid crystals with various lanthanide ions (Eu(III), Sm(III) and Tb(III)) was designed and prepared starting from corresponding lanthanide nitrates and N-alkylated 4-pyridones derivatives with mesogenic 3,4,5-tris(alkyloxy)benzyl moieties (alkyl= hexyl, octyl, decyl, dodecyl, tetradecyl or hexadecyl). These new lanthanidomesogens were investigated for their mesogenic properties by a combination of differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and temperature dependent powder X-ray diffraction (XRD). Additionally, their thermal stability was assessed by thermogravimetric analysis (TG). All these complexes display an enantiotropic liquid crystalline behavior with either a lamellar (SmA), in the case of shorter chains analogues (6 and 8 carbon atoms) or a hexagonal columnar (Colh) phase, for complexes with higher number of carbon atoms (12, 14 and 16), assigned on the basis of their characteristic texture and XRD studies. For complexes with an intermediate number of carbon atoms in the side chains (10), both a lamellar phase at lower temperatures and a Colh phase at higher temperatures were evidenced. In solid state, all these complexes show characteristic emissions assigned to the corresponding lanthanide ion. In addition, the luminescence decay curves showed single exponential decays with the characteristic times in the ms range (0.75-0.90 ms for Eu(III), 0.045-0.060 ms for Sm(III) and 0.75-1.05 ms for Tb(III), respectively).