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Title: Effect of disubstitution pattern of the terminal alkyl chains on the mesophase of liquid crystals based on lanthanide(III) complexes: A study of the thermal, emission and dielectric behavior
Authors: Ilinca, Theodora 
Chiriac, Florentina Laura 
Ilis, Monica 
Manaila-Maximean, Doina 
Ganea, Paul 
Pasuk, Iuliana 
Circu, Viorel 
Affiliations: University of Bucharest, Romania 
National Research and Development Institute for Industrial Ecology, ECOIND 
University of Bucharest, Romania 
University Politehnica of Bucharest, Romania 
National Institute Materials Physics 
National Institute Materials Physics 
University of Bucharest, Romania 
Keywords: Liquid crystals;Lanthanidomesogen;4-Pyridone;Dielectric spectroscopy
Issue Date: May-2022
Publisher: Elsevier
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
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.
Journal of Molecular Liquids, vol. 360, 2022,
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