Electronic structure and optical properties of Eu(III) tris-β-diketonate adducts with 1,10-phenanthroline

Luminescent 1,10-Phenanthroline β-Diketonate Europium Complexes with Large Second-Order Nonlinear Optical Properties

Substitution of the diglyme ligand of [Eu(hfa)₃(diglyme)] (where hfa is hexafluoroacetylacetonate) with a simple 1,10-phenanthroline leads to a six-fold increase of the product μβ_EFISH, as measured by the Electric-Field-Induced Second Harmonic generation (EFISH) technique. Similarly, [Eu(tta)₃(1,10-phenanthroline)] (where Htta is 2-thenoyltrifluoroacetone) is characterized by a large second-order NLO response. Both 1,10-phenanthroline europium complexes have great potential as multifunctional materials for photonics.

Optical properties and electronic structure of Eu(III) complexes with HMPA and TPPO

Two adducts of Eu(III) tris-hexofluoroacetylacetonate with HMPA (OP(N(CH₃)₂)₃, hexamethylphosphotriamide) and TPPO (OP(C₆H₅)₃, triphenylphosphine oxide) were studied by optical spectroscopy and quantum chemistry (DFT/TD-DFT). The structure of the higher occupied molecular orbitals (MO) of the two adducts determines differences in the position of the excitation band maximum of hfac ligands. According to the calculation data, all excited states are caused by the transition to 3 vacant π₄* MOs of hfac ligands. Optical spectra of absorption, excitation and luminescence are obtained and interpreted. The peculiarity of the HOMO-LUMO structure, the low value of the energy gap, and the broadened absorption region of hfac ligands compensate the low absorbance ability of the groups N(CH₃)₂ in a region of 220-360 nm for the adduct Eu(hfac)₃(HMPA)₂, reducing the luminescence intensity by only 5-10% relative to the adduct of the Eu(III) complex with TPPO ligands.

Electronic structure and optical properties of Ln(III) nitrate adducts with 1,10-phenanthroline

Adducts of tris-nitrates of rare-earth elements Ce(III), Nd(III), Eu(III), and Er(III) with two molecules of 1,10-phenanthroline with formula Ln(NO₃)₃(Phen)₂ are studied by X-ray photoelectron spectroscopy (XPS) and quantum chemistry (DFT/TDDFT). The geometric structure for DFT modeling is build using X-ray diffraction data. To analyze the composition and differences of the electronic structure in the series under study, XPS spectra were obtained for which interpretation was performed using calculated data. It has been shown that the molecule of Phen, when attached to the complexes of nitrates, is polarized, leads to an increase in absorption in the visible region and reduces the energy gap between HOMO and LUMO. Experimental absorption spectra were obtained, described and interpreted using TDDFT simulation. The transitions in adducts from π to π * MO in Phen ligands determine the main absorption band. The reasons for the absence of luminescence in adducts with ions Ce(III), Nd(III), and Er(III) are revealed by the example of the correlation diagram of singlet and triplet levels. A possible origin of coloring of adducts is determined using TDDFT.

Europium(III) complex with powerful antenna ligands: Interligand interaction

The luminescent properties of europium(III) trifluoroacetate [Eu(TFA)3bipy·3Н2О]∙bipy (I), where TFA - trifluoroacetate anion and bipy - 2,2'bipyridyl were investigated. Despite the presence of two efficient antenna ligands in complex (bipy1 in europium coordination sphere and bipy2 in the outer-sphere) the complex displays weak luminescence. By employing density functional theory-based methods, the luminescence, electron structure, interligand interactions and the processes of energy transfer in I were investigated. The nature of the chemical bond in I was studied by the natural bond orbital analysis. The mechanism of luminescence weakening in the complex was ascertained: competitive energy transfer from coordinated bipy1 ligand on to outer-sphere bipy2 molecule results in appreciable weakening of the antenna effect.