Impact of n,γ-irradiation on organic complexes of rare earth metals.

The complexes of La, Ce, Nd, Sm, Eu, Tb and Yb with benzoxazolyl-phenolate, benzothiazolyl-phenolate, benzoxazolyl-naphtholate, benzothiazolyl-naphtholate and 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione ligands were treated with n,γ-irradiation upon a sustained (45 h, absorbed dose of 120 krad, flux of neutrons 5·1013 n/cm2) and a pulse mode (3 ms, absorbed dose of 130 krad, flux of neutrons 3.6·1013 n/cm2). It was found that main characteristics of the compounds (shape of substance, color, IR absorption and photoluminescent spectra) have not changed. With an example of cerium complex [Ce(OON)3]2 it was revealed that the molecular structure of compounds after strong pulse irradiation also does not changed. However, computer simulations of neutron exposure on the same complexes showed significant shift of metal atoms and ligands. Possible reasons for the detected discrepancy between experimental and calculated data are discussed.

X-Ray excited luminescence of organo-lanthanide complexes.

A comparative study of the photoluminescence (PL) and radioluminescence (RL) of lanthanide complexes with benzimidazolylphenolate (NON), 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate (TTA) and 1,3-acetylacetonate (acac) ligands revealed significant differences in the total and relative intensity of emission. The PL spectra contain both bands of metal-centered and ligand centred emission while X-ray excited compounds display only the bands of Ln3+ ions, the relative intensity of which differs from that in UV excited analogues. The RL intensity of all the studied complexes is about 300 times lower than that of PL. Increasing the cathode current and tube voltage enhances the RL efficiency insignificantly. Simultaneous irradiation of the sample with X-ray and UV radiation leads to a corresponding increase in the intensity of emission. A possible mechanism of RL of organo-lanthanide complexes is discussed.

Features of the Molecular Structure and Luminescence of Rare-Earth Metal Complexes with Perfluorinated (Benzothiazolyl)phenolate Ligands.

A set of Sc, Nd, Sm, Eu, Ho, Gd, Er, Yb complexes with perfluorinated 2-(benzothiazol-2-yl)phenolate ligands Ln(SONF)3(DME) were synthesized by the reactions of silylamides Ln[N(SiMe3)2]3 with phenol H(SONF). The structure of the initial phenol, Sc, and Er complexes was established using X-ray analysis, which revealed that the obtained compounds are mononuclear, in contrast to the binuclear non-fluorinated analogues [Ln(SON)3]2 synthesized earlier. All the obtained complexes, both in solid state and in tetrahydrofuran (THF) solutions, upon excitation by light with λex 395 or 405 nm show intense luminance of the ligands at 440-470 nm. The Eu complex also exhibits weak metal-centered emission in the visible region, while the derivatives of Sm luminesces both in the visible and in the infrared region, and Nd, Er, and Yb complexes emit in the near IR (NIR) region of high intensity. DFT (density functional theory) calculation revealed that energy of frontier orbitals of the fluorinated complexes is lower than that of the non-fluorinated counterparts. The level of highest occupied molecular orbital (HOMO) decreases to a greater extent than the lowest occupied molecular orbital (LUMO) level.

Sensitization of NIR luminescence of Yb3+ by Zn2+ chromophores in heterometallic complexes with a bridging Schiff-base ligand.

Herein, complexes [ZnL]2 (1), {(H2O)Zn(µ-L)Yb[OCH(CF3)2]3} (2), {[(CF3)2HCO]Zn(µ-L)Yb[OCH(CF3)2](µ-OH)}2 (3), and [(H2O)Ln2(L)3] (Ln = Yb (4) and Gd (5)) containing a bridging Schiff-base ligand (H2L = N,N'-bis(3-methoxy salicylidene)phenylene-1,2-diamine) were synthesized. The compounds 1-4 were structurally characterized. The ytterbium derivatives 2-4 exhibited bright NIR metal-centred photoluminescence (PL) of Yb3+ ion under one- (λex = 380 nm) and two-photon (λex = 750 nm) excitation. The superior luminescence properties of complex 2, which was suggested as a marker for NIR bioimaging, were explained via the strong absorption of the 375 nm LMCT state of the ZnL chromophore, efficient energy transfer from ZnL towards Yb3+ through a reversible ligand-to-lanthanide electron transfer process, and absence of luminescence quenchers (C-H and O-H groups) in the first coordination sphere of the rare-earth atom.

Luminescent properties of 2-mercaptobenzothiazolates of trivalent lanthanides.

A series of lanthanide complexes (Ln = Nd, Sm, Eu, Gd and Yb) with anionic 2-mercaptobenothiazolate (mbt) ligands were synthesized. Depending on the solvents chosen for the synthesis, Ln(mbt)3(THF)2 and Ln(mbt)3(Et2O) complexes were precipitated from THF and Et2O solutions respectively. The structure of Yb(mbt)3(Et2O) was determined by X-ray analysis. Photophysical properties of the complexes were studied. It was found that under photoexcitation Nd and Yb derivatives exhibit bright metal-centered luminescence in the NIR region while Sm(mbt)3(THF)2 demonstrates intensive visible emission corresponding to (4)G5/2 → (6)HJ (J = 5/2, 7/2, 9/2, 11/2) f-f transitions of Sm(3+) along with NIR emission of moderate intensity. In the case of europium compounds as well as Sm(mbt)3(Et2O) no luminescence was detected. It is assumed that the difference in photoluminescence of Yb and Eu complexes can be explained by an intramolecular electron transfer process, which efficiently proceeds in these compounds.

8-Quinolinolate complexes of yttrium and ytterbium: molecular arrangement and fragmentation under laser impact.

New 8-quinolinolate (Q) complexes of yttrium (1) and ytterbium (2) were synthesized by the reactions of Cp3Y and Yb[N(SiMe3)2]3 with 3 equiv. of 8-hydroxyquinoline in a DME solution. Single crystal X-ray analysis revealed the trinuclear molecular structure of the compounds Ln3Q9. The LDI-TOFMS investigation displayed that under the laser impact the compounds split off Q(-) anions to give Ln3Q8(+), Ln2Q5(+) and LnQ3(+) moieties. In the negative mode spectra the anions Q(-) and LnQ4(-) were observed. The DFT calculations showed the decreased stability of cationic Ln-quinolinolate as compared with their anionic counterparts. Complex 2 which is used as an emitter in a three-layer OLED displayed a metal-centered emission at 979 nm and an intensity of 50 µW cm(-2) at 15.5 V.

Anhydrous mono- and dinuclear tris(quinolinolate) complexes of scandium: the missing structures of rare earth metal 8-quinolinolates.

The first monomeric anhydrous scandium tris(8-quinolinolate) complex 1 with the 2-amino-8-quinolinolate ligands and the Sc(2)Q(6) dinuclear complex 2 with the unsubstituted 8-quinolinolate ligands have been synthesized and characterized by X-ray analysis and DFT calculations. The intramolecular hydrogen bonds appear to be responsible for the unique monomeric structure of complex 1. The DFT-based analysis of the electron density topology reveals the (3,-1) critical points corresponding to the O···H and N···H bonds. The two scandium atoms in compound 2 are inequivalent due to different ligand surroundings. They are coordinated by seven (5O, 2N) and eight (4O, 4N) ligand atoms. The increase in the coordination number is accompanied by a decrease in the positive charge of the metal atom as evidenced by the DFT calculations.

Synthesis, structures, and electroluminescent properties of scandium N,O-chelated complexes toward near-white organic light-emitting diodes.

Three members of a new class of electroluminescent, neutral, and monomeric scandium N,O-chelate complexes, namely, Sc(III)-tris-2-(2-benzoimidazol-2-yl)phenolate (1), Sc(III)-tris-2-(2-benzoxyazol-2-yl)phenolate (2), and Sc(III)-tris-2-(2-benzothiazol-2-yl)phenolate (3), have been prepared and X-ray characterized. DFT calculations have been performed. In contrast to the most frequently applied dual or multiple dopants in multilayer white OLED devices, all our simpler devices with the configuration of indium tin oxide/N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine/neat scandium complex/Yb exhibit close to near-white emission with a blue hue (CIE(x,y) = 0.2147, 0.2379) in the case of 1, a cyan hue (0.2702, 0.3524) in the case of 2, and a yellowish hue (0.3468; 0.4284) in the case of 3.