Sparkle Model Research Articles

Synthesis, spectroscopic studies and structure prediction of the new Tb(3-NH 2PIC) 3·3H 2O complex

The synthesis, spectroscopic properties and structure prediction of the complex of Tb(III) with 3-aminopyridine-2-carboxylic acid (3-NH 2PIC) are described. The complex was characterized by elemental analysis and IR, absorption and emission spectra. The C, H and N elemental analysis consistent with the formulation of the compound as Tb(3-NH 2PIC) 3·3H 2O. This complex exhibits a luminescence intensity that is attenuated to that of its Eu +3 congener. The Sparkle model, used for structural computations of lanthanide complexes (SMLC), was applied to the new complex. The calculation used an INDO/S-CI model for determination of the electronic spectrum.

Experimental and theoretical study of ligand field, 4f–4f intensities and emission quantum yield in the compound Eu(bpyO 2) 4(ClO 4) 3

The high resolution emission spectrum of the Eu 3+ ion in the compound Eu(bpyO 2) 4(ClO 4) 3, where bpyO 2=2,2′-bipyridine-1,1′-dioxide, has been previously studied in solid state and frozen solution. The compound crystallizes in the monoclinic P2 1 space group with the cell parameters a=14.730(1) Å, b=13.585(1) Å, c=22.967(2) Å and β=91.46(1)°. The coordination polyhedron can be described as a distorted cube into a square antiprism with symmetry close to D 2. The experimental emission quantum yield ( q) was measured according to a method previously described and a q-value of 15% was obtained. By using the structural crystallographic data a theoretical ligand field and intensity analysis was carried out, and the sparkle model was applied to obtain the electronic structure of the organic part of the compound. From these results, intramolecular energy transfer rates were evaluated according to a recently developed model. An appropriate set of rate equations for the normalized populations of the levels involved was solved numerically, by using the 4th order Runge–Kutta method, and a theoretical q-value could be obtained (19.6%), which is in good agreement with experiment. A relevant aspect is that the reason for this rather low q-value could be explained in terms of the relative position of the lowest ligand triplet energy level with respect to the 5D 1 and 5D 0 levels of the Eu 3+ ion. The theoretical analysis has also shown that, in this compound, a slight decrease in the energy of the ligand triplet level is sufficient to quench almost completely the Eu 3+ luminescence.

Sparkle model and intensity parameters of the Eu(3-amino-2-carboxypyridine-N-oxide)33H2O complex

The sparkle model for structural calculation of lanthanide complexes (SMLC) was applied to the Eu(3-aminopyridine-2-carboxylic acid N-oxide)3H2O, a new lanthanide complex recently synthesized. For the calculation of the electronic spectra of the complexes, the sparkle is replaced by a point charge with the ligands held in the positions as determined by the SMLC, and uses an INDO/S-CI model. A good agreement between theoretical and experimental UV absorption spectra of the complex has been obtained. This result increased our confidence in the predicted structure. The optimized spherical coordinates of the ligands were then used to perform theoretical predictions of the Judd–Ofelt intensity parameters (Ωλ,λ=2and4), the 5D0→7F0/5D0→7F2 intensity ratio and the 5D0→7F1 transition splitting using the simple overlap model (SOM). The satisfactory results obtained in this system are an indication that both SMLC and SOM can lead to reliable prediction of complex structure and 4f–4f intensities.

Design of ligands to obtain lanthanide ion complexes displaying high quantum efficiencies of luminescence using the sparkle model

In this paper we exemplify how to use our sparkle model for the calculation of lanthanide complexes (SMLC-AM1-INDO/S-CI) together with Fermi's golden rule with the multipolar and exchange mechanisms to describe the ligand–lanthanide ion energy transfer for the purpose of designing ligands to obtain complexes displaying high quantum efficiencies of luminescence. Accordingly, we propose aromatic imides as efficient antennas and energy transfer ligands when coordinated to Eu 3+ ion. More specifically we designed Eu(btfai) 3bipy (btfai=benzoyltrifluoroacetylimide anion and bipy=bipyridine) and Eu(bzaci) 3bipy (bzaci=benzoylacetylimide anion) which we then compare with their β-diketone analogues Eu(btfa) 3bipy (btfa=benzoyltrifluoroacetonate) and Eu(bzac) 3bipy (bzac=benzoylacetonate), which have been previously synthesized and whose quantum efficiencies we have also previously measured. Our theoretical results indicate that indeed the quantum efficiencies of Eu(btfai) 3bipy and Eu(bzaci) 3bipy are electronically equivalent to their highly luminescent β-diketone analogues with the advantage of one less hydrogen directly bonded to the central atom of the β-dicarbonylic anionic species. Indeed the possibility of vibronic coupling through that bond vibrational mode, which may be partially quenching the luminescence from the 5D 0 level of the Eu 3+ ion in the β-diketone analogues case, is thus eliminated.

A theoretical approach to intramolecular energy transfer and emission quantum yields in coordination compounds of rare earth ions

A recently developed theoretical approach to the evaluation of ligand–rare earth ion energy transfer rates in coordination compounds is discussed in the context of a scheme for the modeling of highly luminescent rare earth compounds. This scheme is based on the joint application of the theory of 4f–4f transition rates (radiative and nonradiative), the sparkle model to describe the electronic structure of the organic part and coordination geometries of the compounds, and the present theoretical approach to intramolecular energy transfer processes.

Uma metodologia para o projeto teórico de conversores moleculares de luz

Recentlly, we have proposed the representation of lanthanides within AM1 as sparkles for the purpose of obtaing ground state geometries of their complexes. We tested our quantum chemical sparkle model (SMLC/AM1) for the prediction of the crystallographic structure of complexes with coordination number nine, eight and seven. A technique is introduced for the theoretical prediction of eletronic spectra of the organic part of lanthanide complexes by replacing the metal ion by a point charge with the ligands held in their positions as determined by the SMLC/AM1, and by computing the theoretical spectra via the intermediate neglect of differential overlap/spectroscopic-configuration interaction (INDO/S-CI).

Spectroscopic properties of a new light-converting device Eu(thenoyltrifluoroacetonate) 3 2(dibenzyl sulfoxide). A theoretical analysis based on structural data obtained from a sparkle model

We report the synthesis, characterization and spectroscopic properties of the compound Eu(thenoyltrifluoroacetonate), 2(dibenzyl sulfoxide) which is highly luminescent under UV excitation. Experimental and theoretical results on ligand field parameters, 4f-4f intensities and intramolecular energy transfer processes are described. The characteristic emission spectrum of the Eu 3+ ion shows a very high intensity for the hypersensitive 5D 0 → 7F 2 transition, pointing to a highly polarizable chemical environment around the Eu 3+ ion. No emission at low temperature from the organic part of the compound is observed, in contrast to the case of the analog compound with Gd 3+, indicating that energy transfer from the ligands to the Eu 3+ ion is quite efficient. Lifetime measurements confirm that the Eu 3+ luminescence has a higher efficiency than in the case of the hydrated compound (two water molecules in the place of the dibenzyl sulphoxides). The theoretical calculations are based on an optimized coordination geometry and electronic structure obtained from the SMLC/AM1 (Sparkle Model for the calculation of lanthanide complexes within the Austin Model 1), recently introduced in the literature, and ligand field and 4f-4f intensity models previously developed. A comparison with experiment is made. Considerably high values of intramolecular energy transfer rates are predicted.

Modeling Lanthanide Complexes: Towards the Theoretical Design of Light Conversion Molecular Devices

Theoretical techniques have been developed and/or improved to predict the molecular structure of lanthanide complexes which were used to calculate their electronic properties, in particular, their electronic spectra and energy levels necessary to calculate the rates of energy transfer from the ligands to the metal ion. The molecular structure has been obtained by the SMLC/AM1 (Sparkle Model for the Calculation of Lanthanide Complexes – Austin Model 1) model where the lanthanide ion is simulated by a sparkle implemented into the AM1 Hamiltonian used to perform a HF-SCF (Hartree-Fock Self-Consistent Field) calculation. The previous implementation of the SMLC/AM1 model (sparkle/1) involving only two parameters has been generalized to be consistent with the AM1 Hamiltonian and the new model (sparkle/2) significantly improved the prediction of molecular structures of Eu(III) complexes. For the electronic spectra and energy level calculations of the lanthanide complexes the model replaces the metal ion by a point charge with the ligands held in their positions as determined by the SMLC/AM1 model, and uses a INDO/S-CI (intermediate neglect of differential overlap/spectroscopic-configuration interaction) model. A preliminary study of the solvent effects on the absorption spectra of the free ligand is also presented. For the ligand-lanthanide ion energy transfer Fermi's golden rule is used with the multipolar and exchange mechanisms being implemented and tested for several complexes. These theoretical techniques have been applied to several complexes yielding very good results when compared to experimental data as well as predictions for the molecular and electronic structures and the relative contributions of the mechanisms for the energy transfer rates.

Sparkle model for the quantum chemical AM1 calculation of europium complexes of coordination number nine

Recently, we have proposed the representation of lanthanides within AM1 as sparkles for the purpose of obtaining ground state geometries of their complexes. In the present work we tested our quantum chemical sparkle model for the prediction of the crystallographic structure of tris (dipivaloylmethanato) (2,2′:6′,2′'-terpyridine) of europium(III), a complex with coordination number nine. Considering the coordination polyhedron, the interatomic distances averaging 2.83 Å and the bond angles could be predicted with an average deviation of 0.12 Å and 5° respectively. This finding reinforces our model and consequently the notion that the lanthanide-ligand interaction is essentially electrostatic.

Sparkle model for the quantum chemical AM1 calculation of europium complexes

Considering that the bonds between a lanthanide and its ligands essentially possess an electrostatic character, we propose the representation of rare-earth elements within AM1 as sparkles. To parametrize the sparkle model we have used the known geometry of the complex tris (acetylacetonate) (1,10-phenantroline) of europium (III). Interatomic distances for the coordination polyhedron, averaging 2.81 Å, could be predicted with an average deviation of 0.13 Å. In short, this is a simple lanthanide-ligand electrostatic model which simultaneously treats the organic ligands and their interactions with the powerful AM1 method, yielding results of useful accuracy.