The effects of structure and ligand variations on the luminescence of Europium (III) complexes
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Date
2018-02
Authors
Alexander, Orbett Teboho
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
The chemistry of lanthanides has expanded immensely across many scientific fields over the
years and that was mainly due to the rare versatility exhibited by the spectroscopic and
magnetic nature of these metals in the series. With the coordination nature of these
lanthanoids not governed by the orbital directionality, as is the case with transition metals, the
relative coordination chemistry of this series becomes of great interest and therefore is
susceptible to ground breaking science across many scientific disciplines. Europium (III)
metal ion in particular, has been involved in many scientific fields due to its sterling
spectroscopic properties. Its ternary analogues have been extensively employed as emitting
layers in the edifice of optoelectronic devises. Moreover, its applications extend as far as
tailoring active luminescence bioprobes in biomedical sciences which is a vast field with a lot
of other related applications in it. The main interest has always been its red narrow emission
spectral profile which is susceptible to any organic matrix it is submerged in.
The principle aim of this study was to gain insight into the chemistry, coordination and
photoluminescence behaviour of ternary EuIII based complexes. From this idea, it was
decided to synthesize a few novel ligand systems. This include (E)-1-((9-ethylcarbazol-3-
ylimino)methyl)-napthanol, (E)-2-(9-ethylcarbazol-3-yliminomethyl)-6- methoxy phenol,
(E)-2-methoxy-(6-(phenyliminomethyl))-phenol, (E)-1-((2-(pyridin-2-yl)hydrazono) methyl)
naphthalene-2-ol, (E)-2-methoxy-6-((2-(pyridin-2-yl)hydrazono)methyl)phenol, (E)-2-(2-((2-
hydroxynaphthalen-1-yl)methylene)hydrazinyl) quinolin-8-ol and (E)-2-(2-(2-hydroxy-3-
methoxybenzylidene)hydrazinyl) quinolin-8-ol characterized by means of IR, UV/Vis and
NMR (1H, 13C) spectroscopy. Furthermore, the solid state structural characterization was
carried out using single crystal X-ray diffraction spectroscopy for compounds with suitable
single crystals X-ray diffraction collection. However, the intended tailoring of ternary EuIII
complexes with this novel ligand species was not successful. The ligand systems synthesized
were designed with the idea to be potentially biologically active and fluorescent by itself.
They were analysed for photoluminescence properties and were successfully found to be
luminous and are to be sent for cell testing.
A range of ternary EuIII based complexes, of the form [Eu(β-diketone)3 X]
(X = 1,10-phenanthroline), were synthesized by using selected acetyl acetone derivatives
(β-diketone) as parallel ligand system used in this study. The bidentate β-diketone ligands
used are 1,3-Diphenyl-propanedione (DBM), 2) 4,4,4-Trifluoro-1-chlorophenyl-butanedione
(TCPB), 3) 2-Bromo-1,3-diphenyl-propanedione (DBBrM), 4) 3-Chloro-2,4-pentanedione
(DMC), 5) 3,3-Dimethyl-2,4-pentanedione (DMMP), and 6) Benzoic anhydride (BZAN). The
EuIII based analogues with the bidentate β-diketone ligand given above were successfully
synthesized and characterized by means of IR, X-ray diffraction and Elemental Analysis
spectroscopy. These obtained ternary EuIII based complexes are [tris-(4,4,4-Trifluoro-1-
chlorophenyl-butanedione) mono(1,10-phenanthroline) europium(III)], [tris-(2-Bromo-1,3-
diphenyl-propanedione) mono(1,10-phenanthroline) europium(III)], [tris-(1,3-Diphenylpropanedione)
mono (1,10-phenanthroline) europium(III)], [tris-(3-Chloro-2,4-pentanedione)
mono(1,10-phenanthroline) europium(III)], [tris-(2,2,6,6-Tetremethyl-heptanedione)
mono(1,10-phenanthroline) europium(III)], tris-(Benzoic Anhydride)-mono-(1,10-
phenanthroline) europium(III)] and {[hexa-( Benzyl carboxylic acid) bis-(1,10-
phenanthroline) di-europium(III)]-μ-[κ2-O,O’-( benzyl carboxylic acid)]2}. These above
stated ternary EuIII complexes were analysed for photoluminescence and all proved to be
luminous. However, there were significant differences in the spectral identity of these
respective complexes and that was due to the ligand nature coordinated to the EuIII metal ion.
The observed spectral identities are defined in terms of relative Stark splitting of the
complexes which is induced by the symmetry imposed on the EuIII ion by the atomic
orientations around the metal. The atomic orientations around the EuIII metal ion are dictated
by the steric hindrance imposed by the peripheral derivatization on the acetyl acetone back
bone. It was crystallographically deduced that the high quantum yield (82%) of complex
[tris-(4,4,4-Trifluoro-1-chlorophenyl-butanedione) mono(1,10-phenanthroline)
europium(III)] was due to strong binding of the antenna ligand to the metal ion, facilitating
efficient energy transfer to give high luminous efficiency.
There were successful correlations drawn between the photoluminescence and the
crystallographic data obtained of the [Eu(β-diketone)3 X] (X = 1,10-phenanthroline)
complexes. The respective point groups from both disciplines could be matched. However,
the polyhedron constructed for atoms directly bonded to the EuIII metal ion indicates higher
symmetry point groups due to observed polyhedral distortions therein. The correlation of data
from these two scientific disciplines rubber stamp the proof of concept of using the method
detailed in this study in analysis of the site symmetry of the EuIII metal ion in bulk organic
system, UPNP or any other organic system for that matter.
Description
Keywords
Lanthanides, Europium (III) metal ion, Luminescence bioprobes, Photoluminescence, Chemistry, Thesis (Ph.D. (Chemistry))--University of the Free State, 2018