Novel wide-range columnar and lamellar photoluminescent liquid crystalline lanthanides complexes with mesogenic 4-pyridone derivatives

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).