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Polarized emission and dielectric studies of

novel lanthanidomesogens based on 4-pyridone ligands Theodora A. Ilincă1, Doina Mănăila-Maximean2, Paul C. Ganea3, Iuliana Pasuk3, Viorel Cîrcu1*

1Department of Inorganic Chemistry, University of Bucharest, 23 Dumbrava Rosie st, Bucharest 020464, Romania 2University Politehnica of Bucharest, Department of Physics, Spl. Independentei 313, Bucharest, R-060042, Romania

3National Institute of Materials Physics, P.O. Box MG-7, Magurele, 077125, Romania

A series of novel lanthanidomesogens based on lanthanide nitrates carrying three 4-pyridone ligands

having two alkoxy chains at the periphery have been designed and investigated (Scheme 1).

Scheme 1. Synthesis of lanthanide(III) complexes.

Structural characterization and purity

Elemental Analysis IR spectroscopy

Table 1. Results of the elemental analysis.

Thermal behaviour and mesophase assignment Table 3. Thermal parameters for the new compounds.

Cr, Cr1, Cr2, Cr3: crystalline phases

Colh: hexagonal columnar phase

Iso: isotropic phase

*transition detected by POM.

Thermogravimetric analysis

Introduction/Samples

Results

These compounds were investigated by a combination of :

• Differential scanning calorimetry (DSC), Diamond DSC Perkin Elmer, 10oC/min rate

• Polarizing optical microscopy (POM), Nikon 50iPol microscope equipped with a Linkam THMS600 hot stage and

TMS94 control processor

• The thermal stability was studied by thermogravimetric analysis (TG), TA Q50 TGA

• C, H, N analyses were carried out with an EuroEA 3300 instrument

• Emission spectra, OceanOptics QE5PRO spectrometer attached to the microscope and using a Nikon Intensilight

excitation source

• Polarized emission studies, DC LAB POWER SUPPLY LABPS3005N, measured on a cell with planar alignment with

9 µm thickness

• IR spectra were recorded on a Bruker spectrophotometer using KBr discs

• 1H and 13C NMR spectra were recorded on a Bruker spectrometer operating at 300 MHz, using CDCl3 as solvent

• Broadband Dielectric Spectrometer, NOVOCONTROL Technologies GmbH & KG with an Alpha-A high-performance

frequency analyzer in the LF domain (0.01 to 107 Hz), equipped with WinDETA software

Methodology/Instrumentation/Experimental

• All Eu(III), Sm(III) and Tb(III) complexes show strong and characteristic emission spectra in both solid state and

liquid crystalline.

• For the lanthanide complexes, DSC and POM data indicate the formation of an enantiotropic liquid-crystalline phase

identified as hexagonal columnar mesophase, confirming the structural role of the metal ion.

• The melting temperatures of the lanthanide complexes do not depend on the size of the lanthanide(III) ion.

• The compounds show a high thermal stability (up to 270oC).

• One Eu(III) compound (5-14/Eu) has been selected for polarized emission studies in a mixture with E7 (E7:5-14/Eu =

97:3) and a polarization ratio of 1.3 has been measured.

• The dielectric loss spectra versus frequency shows that, bellow the phase transition temperatures, the spectra have a

monotonous descending shape. At temperatures above the LC phase transition, the spectra present a maximum,

appearing at relatively low frequencies (1-100 Hz), and shifting towards higher frequencies at the temperature increase.

Conclusions

PCG thank the Romanian Ministry of Education and Research for financial support under Core Program, Project

21N/2019

References

Acknowledgement

[1]. K. Binnemans, Lanthanidomesogens in Handbook on the Physics and Chemistry of Rare Earths, vol. 43, pp. 1-154,

eds. J.-C. G. Bünzli, and V.K. Pecharsky, Elsevier (2013).

[2]. J.-C. G. Benzli, C. Piguet, B. Donnio, D. Guillon, Chem. Commun., 2006, 3755.

[3]. K. Binnemans, C. Görller-Walrand, Chem. Rev., 102, 2303 (2002).

[4]. A. A. Knyazev, A. S. Krupin, B. Heinrich, B. Donnio, Y. G. Galyametdinov, Dyes and Pigments, 148, 492 (2018).

[5]. Y. G. Galyametdinov, A. A. Knyazev, V. I. Dzhabarov, T. Cardinaels, Kr. Driesen, C. Görller‐Walrand, K.

Binnemans, Adv. Mater., 20, 252 (2008).

[6]. L. F Chiriac, I. Pasuk, M. Secu, M. Micutz, Chem. Eur. J., 24, 13512 (2018).

[7]. L.F. Chiriac, P.C. Ganea, D. Manaila-Maximean, I. Pasuk, V. Cîrcu, J. Mol. Liq., 290, UNSP 111184 (2019).

[8]. A. Pană, F. L. Chiriac, M. Secu, I. Pasuk, M. Ferbinteanu, M. Micutz, V. Cîrcu, Dalton Trans., 44, 14196 (2015).

Compound Transition, T/°C (∆H/kJ*mol-1)

4-12 Cr 96 (64.8) Iso 74 (-56.0) Cr

4-14 Cr 98 (68.1) Iso 79 (-67.1) Cr

5-12/Sm Cr 72 (91.2) Colh 204 (1.4) Iso 205 (-1.4) Colh 68 (-45.7) Cr

5-12/Eu Cr 71 (105.2) Colh 200* Iso 200* Colh 68 (-37.8) Cr

5-12/Tb Cr1 71 (16.2) Cr2 84 (58.6) Colh 216 (0.9) Iso 216 (-1.5) Colh 67 (-24.8) Cr

5-14/Sm Cr 73 (71.6) Colh 214 (1.8) Iso 216 (-0.4) Colh 67 (-23.2) Cr

5-14/Eu Cr1 63 (20.9) Cr2 78 (39.3) Colh 242 (1.8) Iso 244 (-1.1) Colh 61 (-7.7) Cr

5-14/Tb Cr1 63 (17.0) Cr2 82 (46.8) Cr3 109 (2.3) Colh 241 (0.7) Iso 240 (-2.1) Colh 60 (-3.2) Cr

Compound Calculated Found

C H N C H N

4-12 78.07 10.74 2.53 77.59 10.70 2.73

4-14 78.76 11.07 2.30 78.91 11.30 2.30

5-12/Sm 64.92 8.93 4.21 66.45 5.05 3.95

5-12/Eu 64.87 8.92 4.20 64.70 5.68 3.93

5-12/Tb 64.65 8.89 4.19 65.41 5.15 3.97

5-14/Sm 66.53 9.35 3.88 65.14 5.44 4.11

5-14/Eu 66.48 9.35 3.88 69.11 2.88 3.20

5-14/Tb 66.27 9.32 3.86 64.73 5.44 4.45

Compound νCH2 alkyl

(cm-1)

νC-C, νC-N

(cm-1)

νC=O

(cm-1)

νΝO3-

(cm-1)

νC-O

(cm-1)

νC-H

(cm-1)

νM-O

(cm-1)

4-12 2919, 2851 1640, 1468 1563 - 1145 855, 721 -

4-14 2918, 2850 1638, 1468 1560 - 1144 854, 721 -

5-12/Sm 2918, 2850 1635, 1468 1535 1309 1142 855, 721 517

5-12/Eu 2918, 2850 1636, 1467 1536 1314 1141 855, 721 517

5-12/Tb 2919, 2850 1635, 1468 1531 1301 1142 851, 721 517

5-14/Sm 2918, 2850 1636, 1467 1536 1309 1142 855, 721 506

5-14/Eu 2919, 2850 1635, 1467 1530 1300 1142 851, 790 516

5-14/Tb 2920, 2851 1635, 1468 1531 1300 1142 846, 776 516

Polarizing optical microscopy

Polarized emission studies

a) c) d) e)

f) g)

b)

Figure 2. TG curves for the lanthanide

complexes 5-n/Ln.

Figure 3. Temperature-dependent emission spectra for 5-12/Eu

complex on heating from 25oC up to 150oC (a) and 5-12/Tb complex

on heating from 30oC up to 100oC (b)

Table 2. Results of the IR analysis

25 50 75 100 125 150 175 200 225

Hea

t Flo

w (

End

o up

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Temperature/oC

heating

cooling

Cr-Colh Colh-Iso

Iso-Colh

Colh-Cr

Figure 1. DSC first heating–cooling

cycle for 5-12/Sm.

ATOM-N 2020 – 10th EDITION August 20-23, Constanța, România

ADVANCED TOPICS IN OPTOELECTRONICS, MICROELECTRONICS AND NANOTECHNOLOGY

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5-14/Eu

5-14/Tb

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303 K heating

333 K heating

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333 K cooling

303 K cooling

* Author for Correspondence: viorel.circu@chimie.unibuc.ro

Figure 4. Pictures taken at the polarizing optical microscope showing

the optical textures of: 5-14/Sm on cooling at 50°C (a); 5-14/Tb on

cooling at 88°C (b); 5-14/Eu on cooling at 32°C (c); 5-12/Tb on cooling

at 100°C (d); 5-12/Eu on cooling at 168°C (e); 5-14/Eu at 55°C (f) and

5-14/Eu at 55°C under UV light (g).

Dielectric studies

Emission properties

a) b)

Figure 5. Emission spectra for E7 doped with 5-14/Eu during

changing the applied voltage from 0 to 11V, in 1V steps (a) and in

0.35V steps (b).

Figure 6. Pictures of E7 doped with 5-14/Eu at

different voltages, ranging from 0V up to 11V

(from left to right).

Figure 7. Pictures of E7 doped with

5-14/Eu at different voltages,

ranging from 0V up to 15V (from

left to right).

Figure 8. Loss tangent spectra versus frequency, logarithmic scales, at fixed

temperatures 303 K, crystal phase; 333 K - onset of the liquid crystal phase;

363 K and 403 K - liquid crystal phase. Solid interior signs correspond to the

heating cycle and open interior of the signs to the cooling cycle.

a)

b)