A series of 3,4,5-tridodecyloxybenzyl pyridinium salts derived from 4-hydroxypyridine has been designed and prepared. The liquid crystalline properties of these compounds were investigated by polarized optical microscopy, differential scanning calorimetry and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis. The N-3,4,5-tridodecyloxybenzyl-4-pyridone intermediate shows a monotropic columnar hexagonal mesophase ranging from 56 C down to room temperature while the corresponding bromide dodecyl O-alkylated pyridinium salt shows one enantiotropic columnar mesophase and one additional monotropic columnar phase at lower temperatures. Replacing bromide ion (Br ) with other counterions (NO 3 ; BF 4 and PF 6 ) resulted in mesophase suppression. These luminescent pyridinium salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. Photoluminescent properties of the pyridinium salts do not depend significantly on the nature of counterion employed.

In the present work, new luminescent lanthanide complexes with extended mesomorphic range were prepared by coordination with lanthanide ions (Eu3+, Sm3+, and Tb3+) of the new 4-pyridone-based organic ligands (L) with 3,4- (7- n) and 3,5-di(alkyloxy)benzyl (8- n) mesogenic groups and variable length (n = 12 or 14 carbon atoms) onto the benzyl unit. The cumulative results of the elemental analyses as well as the 1 H, 13C NMR, and IR spectroscopies support the structure of the organic derivatives and their lanthanide complexes [LnL3(NO3)3] (9- n/Ln and 10- n/Ln) described in this work. These complexes show characteristic lanthanide solid-state emission, both at room and elevated temperatures corresponding to crystalline, glassy, or liquid crystal states. The long-range SmA phases displayed by all complexes were supported by a combination of characterization methods, including differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and variable-temperature powder X-ray diffraction (XRD). This work shows that the number, substitution pattern, and length of flexible alkoxy chains are important parameters for controlling the phase-transition characteristics of the lanthanide complexes. Complexes with 3,4-disubstituted pattern (9- n/Ln) shows higher clearing temperatures (nearly 60 C for Eu3+, 70 C for Sm3+ and 85 C for Tb3+ complexes) compared to their counterparts with a 3,5-disubstituted pattern (10- n/Ln). Moreover, complexes 9- n/Ln crystallize when cooling their LC phase while complexes 10- n/ Ln are stable in a glassy state at room temperature as a consequence of the different close interdigitated molecular packing evidenced by XRD measurements. Dielectric spectroscopy was employed to detect the changes of order degree specific to each phase (crystalline, LC, or isotropic). The variation of dielectric constant and the electrical conductivity versus temperature shows three transition intervals for selected complexes 10- 14/Sm and 10- 14/Tb, which delimit the main intervals: 45–60 C, 90–110 C; 140–160 C corresponding to the Cr1-Cr2, Cr2 – SmA and SmA-Iso transitions, and agree very well with the DSC results. The change of characteristic time, obtained by Havriliak-Negami fit function, with temperature also provides a very good correlation with the DSC and POM results.

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.