Synthesis and Luminescent Properties of Novel Lanthanide(III) β-Diketone Complexes with Nitrogen p,p‘-Disubstituted Aromatic Ligands

Abstract

Tris-beta-diketonate lanthanide(III) complexes (Ln = Eu, Er, Yb, Tb), of general formula [Ln(acac)3 L(m)], with chelating ligands such as 4,7-disubstituted-1,10-phenanthrolines and 4,4'-disubstituted-2,2'-bipyridines, have been synthesized and fully characterized. The inductive effects of the para-substituents on the aromatic N-donor ligands have been investigated both in the solid and in the solution states. Single-crystal X-ray structures have been determined for the diethyl 1,10-phenanthroline-4,7-dicarboxylate europium and 4,4'-dimethoxy-2,2'-bipyridine erbium derivatives, revealing a distorted square antiprismatic geometry around the lanthanide atom in both cases. The influence exerted by the p,p'-substituents with respect to the nitrogen coordinating atoms on the Ln-N bond distances is discussed comparing the geometrical parameters with those found for the crystal structures containing the fragments [Ln(III)(phen)] and [Ln(III)(bipy)] obtained from the Cambridge Structural Database. The influence exerted by the electron-attracting groups on the coordination ability of the ligands, that in some cases becomes lack of coordination of the lanthanide ions, has been also detected in solution where the loss of the ligand has been followed by UV-vis spectroscopy. Moreover, the use of relatively long alkoxy chains as substituents on the 1,10-phenanthroline ligand led to the formation of a promesogenic lanthanide complex, whose thermal behavior is encouraging for the synthesis of new lanthanide liquid-crystalline species.

Multistep Anchoring Route of Luminescent (5‐Amino‐1,10‐phenanthroline)tris(dibenzoylmethane)europium(III) on Si(100)

“…Ce 3+ ) is also observed. In the case of Eu III β-diketonate complexes, the emission spectra consist of 5 [32,33] In general, luminescence properties of Eu III complexes depend on the energy transfer properties of ligands since excited organic ligands act as light harvesting groups that, in turn, promote intramolecular energy transfer from the triplet state to an excited state of Eu 3+ . [34] Therefore, emission occurs from the lowest excited state ( 5 D 0 ) to the ground state ( 7 F J ) of Eu 3+ and the presence of organic ligands, namely β-diketonates and phenanthroline, whose triplet states are higher in energy than the emissive 5 D 0 excited state determines an efficient energy transfer process.…”

“…[34] Therefore, emission occurs from the lowest excited state ( 5 D 0 ) to the ground state ( 7 F J ) of Eu 3+ and the presence of organic ligands, namely β-diketonates and phenanthroline, whose triplet states are higher in energy than the emissive 5 D 0 excited state determines an efficient energy transfer process. [20,[32][33][34] However, intensities of the emission spectra related to Eu 3+ intra-4f 6 transitions between the 5 D 0 and 7 F 0-4 levels do not depend on the energy transfer mechanisms but on the excitation wavelength [23,34a,35] and on the local environment around the europium ion. [34,36] Figure 7a displays the emission spectra of 1 powders physisorbed on Si in the 560-650 nm range, adopting two excitation wavelengths, λ ex = 265 and 340 nm, corresponding to the absorption of the phenanthroline ligand [32,37] and to the π-π* transition of the β-diketonate, respectively.…”

“…[20,[32][33][34] However, intensities of the emission spectra related to Eu 3+ intra-4f 6 transitions between the 5 D 0 and 7 F 0-4 levels do not depend on the energy transfer mechanisms but on the excitation wavelength [23,34a,35] and on the local environment around the europium ion. [34,36] Figure 7a displays the emission spectra of 1 powders physisorbed on Si in the 560-650 nm range, adopting two excitation wavelengths, λ ex = 265 and 340 nm, corresponding to the absorption of the phenanthroline ligand [32,37] and to the π-π* transition of the β-diketonate, respectively. [32] The spectrum consists of the characteristic sharp emission peaks at 578 ( 5 D 0 Ǟ 7 F 0 ), 590 ( 5 D 0 Ǟ 7 F 1 ) and 611 nm ( 5 D 0 Ǟ 7 F 2 ).…”

“…[34,36] Figure 7a displays the emission spectra of 1 powders physisorbed on Si in the 560-650 nm range, adopting two excitation wavelengths, λ ex = 265 and 340 nm, corresponding to the absorption of the phenanthroline ligand [32,37] and to the π-π* transition of the β-diketonate, respectively. [32] The spectrum consists of the characteristic sharp emission peaks at 578 ( 5 D 0 Ǟ 7 F 0 ), 590 ( 5 D 0 Ǟ 7 F 1 ) and 611 nm ( 5 D 0 Ǟ 7 F 2 ). Emission spectra of Eu-acid-Si and Eu-NHS-Si are shown in parts b and c of Figure 7.…”

Syntheses, Structures and Photophysical Properties of New Heterodinuclear Cd–Ln Coordination Complexes (Ln = Sm, Eu, Tb, Nd, Ho, Er)

“…Numerous ligands can serve as the "antenna", [11] for example β-diketones, flexible carboxylic acids, pyridine derivatives, aromatic carboxylic acids with highly conjugated and rigid structures, and so on. [12][13][14][15][16] Currently, not only is the variety of ligands important, but also introducing transition-metal ions into the system to synthesize d-f heterometallic coordination complexes for enhancing the luminescence of the f block by sensitization of the d block. The absorption bands of the πǞπ* transitions of the ligands are usually located in the ultraviolet region, while the absorption bands (LǞL* or LǞM) of the d block probably lie in the blue region or the longer wavelength region, which will facilitate the energy transfer to the Ln III ions (f block) and reduce the energy wasted.…”