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.

Triboluminescence and crystal structure of the complex [Eu(NО3 )3 (HMPA)3 ]: role of cleavage planes.

The atomic structure of crystals of the [Eu(NО3 )3 (HMPA)3 ] [hexamethylphosphotriamide (HMPA)] complex characterized by an intensive luminescence and triboluminescence was determined using X-ray structural analysis. Noncentrosymmetric crystals have a monoclinic syngony: a = 16.0686 (3), b = 11.0853 (2), c = 20.9655 Å (4), ß = 93.232° (1), space group P21 , Z = 4, ρcalc  = 1.560 g/cm3. The crystal structure is represented by individual С18 Н54 EuN12 O12 P3 complexes linked through van der Waals interactions with clearly expressed cleavage planes. The Eu(III) atom coordination polyhedron reflected the state of a distorted square antiprism. Structural aspects of the suggested model, including formation of triboluminescence properties, were considered and the role of the cleavage planes was discussed.

Triboluminescence and crystal structure of the centrosymmetric complex [Tb(NO3 )2 (Acac)(Phen)2 ]·H2 O.

The atomic structure of crystals of the complex [Tb(NO3 )2 (Acac)(Phen)2 ]·H2 O, (AA - acetylacetonate anion, Phen - 1,10-phenanthroline) characterized by an intensive luminescence and triboluminescence has been determined by means of an X-ray structural analysis method. Centrosymmetric crystals have a monoclinic syngony: a = 11.2298(1), b = 9.6492(1), c = 13.2745(1) Å, ß = 101.290(1), space group P2/n, Z = 2, ρcalc = 1.790 g/cm3 . The crystal structure is represented by individual С29 Н25 N6 O9 Tb complexes linked through van der Waals interactions with clearly expressed cleavage planes. The Tb(III) atom coordination polyhedron reflects the state of a distorted square antiprism. The structural aspects of the suggested model of formation of the triboluminescent properties were considered and the role of the cleavage planes discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Luminescence of solvate of boron difluoride dibenzoylmethanate with benzene: aggregates formation.

The concentration dependence of spectral-luminescence properties of solutions boron difluoride dibenzoylmethanate (DBMBF2) in benzene and chloroform has been studied through stationary and time-resolved emission spectroscopy methods. The formation of J-aggregates in the solution of DBMBF2 in chloroform has been revealed and a crystalline adduct of DBMBF2 with benzene has been obtained. A bright blue adduct luminescence is due only to the luminescence of J-aggregates, unlike the crystals of DBMBF2, for which the luminescence of excimers and J-aggregates has been observed. The quantum chemistry simulation of geometric and electronic structure of the DBMBF2 С6Н6 solvate has been performed, and the absorption spectra of DBMBF2 and it is adduct have been calculated.

Photomobile luminescent polymeric materials on the basis of boron and europium chelates.

The photomechanical effect was found in a polymer composition on the basis of polymethylmethacrylate with embedded molecules of the luminophor incapable to undergo photochemical isomerization (anthracenoylacetonate of boron difluoride and dibenzoylmethanatoeuropiate triethylammonium), unlike other compounds having the above effect. The possibility of the development of a simple upward-downward movement drive on the basis of the above compounds was demonstrated.

Photo-mechanical effect in luminescent polymeric materials.

The photomechanical effect was found for the first time in a polymer composition on the basis of polymethylmethacrylate with embedded molecules of the luminophor dibenzoylmethanate of boron difluoride incapable of undergoing photochemical isomerization, unlike other compounds. A thermal mechanism of photochemical displacement was suggested.

Size-dependent fluorescence of dibenzoylmethanate and ditoluylmethanate of boron difluoride.

Significant differences in the luminescence properties of dibenzoylmethanate and ditoluylmethanate of boron difluoride bulk crystals and microcrystals were detected. The size-dependent blue-to-green colour change of the luminescence is connected with the band intensity redistribution of monomer and excimer luminescence and fluorescence due to interdimer interaction.

Luminescence and reversible luminescence thermochromism of bulk and microcrystals of dibenzoylmethanatoboron difluoride.

Essential differences in the luminescence properties of dibenzoylmethanatoboron difluoride (1) bulk and microcrystals were detected. Analysis of the spectral data showed that in every case the fluorescence spectrum of 1 consisted of three components: monomer fluorescence, excimer fluorescence, and fluorescence related with interdimer interaction. Evolution of luminescence spectra observed with decrease of the crystal size are bound with decrease of monomer fluorescence intensity and considerable growth of intensity of fluorescence related to interdimer interaction. The presence of reversible luminescence thermochromism was discovered for 1: lowering the temperature from 300 to 77 K resulted in essential hypsochromic shift of the luminescence band maximum ( approximately 60 nm) connected with considerable decrease of the distances between the planes of the neighboring molecules ( approximately 0.1 Angstrom) that lead to the weakening of interdimer interaction and intensification of monomer luminescence.