Thermal and Emission Properties of a Series of Lanthanides Complexes with N-Biphenyl-Alkylated-4-Pyridone Ligands: Crystal Structure of a Terbium Complex with N-Benzyl-4-Pyridone

Abstract

This work focuses on the investigation of the liquid crystalline behavior and luminescence properties of the lanthanide complexes of Eu(III), Sm(III) and Tb(III) with N-biphenyl-alkylated-4-pyridone ligands. The organic ligands having a biphenyl group attached via a long flexible spacer with either 9 or 10 carbon atoms were synthesized by the reaction between 4-hydroxypyridine and the corresponding bromide compounds. The chemical structures of the organic and lanthanide complexes were assigned based on elemental analysis, single-crystal X-ray diffraction, 1H, 13C NMR and IR spectroscopies, and thermogravimetric analysis (TGA). The X-ray diffraction analysis of a parent compound shows that the lanthanide ions are surrounded by three monodentate pyridone ligands and three bidentate nitrate ions, giving a 9-coordinate environment. The mesogenic behavior and the type of liquid crystalline phases exhibited by the new complexes were analyzed by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM), and powder X-ray diffraction (XRD) studies. Only the lanthanide complexes with longer spacer (10) display a monotropic SmA phase, typically on a short thermal range (less than 10 °C). The complexes with shorter flexible chains (9) show no liquid crystalline properties with melting temperatures lower than their analogs with longer spacers. The emission spectra recorded in solid state at room temperatures show typical emission bands for each lanthanide ion employed (Eu(III), Tb(III) and Sm(III)).

Synthesis, Phase Behavior and Computational Simulations of a Pyridyl-Based Liquid Crystal System

“…As a result, the LC molecular architectures are designed using anisotropic mesogenic shape factors and principles. Several two-or three-ring compounds based on Schiff base/ester LCs have been reported and their optical behaviors were analyzed to obtain the correlation between the geometry of mesogens and their mesophase behaviors [5][6][7][8][9].…”

Evidence of Counterion Size Effect on the Stability of Columnar Phase of Ionic Liquid Crystals Based on Pyridinium Salts Derived from N-3,4,5-Tri(alkyloxy)-benzyl-4-pyridones

“…The synthetic procedure employed for the preparation of the pyridinium salts with side alkyl chains of the same length is depicted in Scheme 1. The starting 4-pyridone compounds 1a-f were prepared by the N-alkylation of 4-hydroxypyridine based on the protocol reported elsewhere by us [28][29][30][31]. Subsequent O-alkylation with alkyl bromides in refluxing acetonitrile and in the presence of K 2 CO 3 gave the bromide pyridinium salts 2a-e in good yields of 67-81%.…”