Since the description of efficient electroluminescence from aluminium tris(hydroxyquinoline) in the mid 1980s, interest in new complexes and polymers with luminescence properties as emitting layers in light-emitting diodes has steadily increased. Recently, Ln(III) ion complexes have gained in importance for this type of application. Here we review some of the seminal work in the area, along with new developments in the field. The photophysical characterization of complexes of lanthanide ions both in solution and in the solid state allows the determination of which of the complexes might be successfully utilized as emitting layers in light-emitting diodes for display applications. However, the architecture of the device is also of major importance, to allow for good charge transport and recombination and thus obtain pure colors and high emission quantum efficiency.

The unfavorable D3h isomer of the C78 fullerene cage is present in Sc3N@C78, an endohedral fullerene which has been prepared by the trimetallic nitride template process. The crystal structure of the fullerene–porphyrin adduct Sc3N@C78⋅[Co(oep)]⋅1.5 C6H6⋅0.3 CHCl3 (oep=octaethylporphyrin) shows that the scandium atoms are located over the centers of the [6,6] ring junctions of pyracylene patches on the inner surface of the fullerene (see picture).

Two lanthanide-organic frameworks were synthesized via hydrothermal methods. Compound 1 ([(Eu,Tb)(C6H8O4)3(H2O)2].(C10H8N2), orthorhombic, Pbcn, a = 21.925(2) A, b = 7.6493(7) A, c = 19.6691(15) A, alpha = beta = gamma = 90 degrees, Z = 4) takes advantage of the similar ionic radii of the lanthanide elements to induce a mixed-lanthanide composition. Compound 2 ([Tb2(C6H8O4)3(H2O)2].(C10H8N2), orthorhombic, Pbcn, a = 21.866(3) A, b = 7.6101(10) A, c = 19.646(3) A, alpha = beta = gamma = 90 degrees, Z = 8) is the terbium-only analogue of compound 1. Solid-state measurements of their luminescence behavior demonstrate that the neutral guest molecule (4,4'-dipyridyl) residing in the extraframework channels is successful in sensitizing lanthanide ion emission. In compound 1, columinescence occurs, and both lanthanide ions show emission. Additionally, quantum yield and lifetime measurements support the premise that the Tb3+ center is also acting to sensitize the Eu3+, effectively enhancing Eu3+ emission.

The Er n Sc3 - n N@C80 (n = 0−3) family of four endohedral fullerenes has been prepared by vaporization of graphite rods packed with 2% Sc2O3/3% Er2O3/95% graphite powder in a Krätschmer−Huffman fullerene generator under dynamic flow of helium and dinitrogen. ErSc2N@C80 has been isolated in pure form via three stages of high-pressure liquid chromatography and characterized by mass spectrometry. The first structure of a mixed metal endohedral, ErSc2N@C80, has been determined by single-crystal X-ray diffraction at 90 K on ErSc2N@C80·CoII(OEP)·1.5C6H6·0.3CHCl3, which was obtained by diffusion of a solution of ErSc2N@C80 in benzene into a solution of CoII(OEP) (OEP is the dianion of octaethylporphyrin) in chloroform. The structure of ErSc2N@C80 consists of a planar ErSc2N unit surrounded by an icosahedral C80 cage. The nominal Er−N distance is 2.089(9) Å and the Sc−N distance is, as expected, shorter, 1.968(6) Å. Despite its location within the C80 cage, the ErSc2N unit displays a remarkable degree of order within the solid-state structure. The metal ions make close contact with individual carbon atoms of the cage with shortest Sc−C distances, in the range of 2.03−2.12 Å, and shortest Er−C distances of 2.20 and 2.22 Å. Two different, but equally populated, orientations of the Ih C80 cage were required to describe the fullerene portion of the structure. Although these C80 cages are located on a crystallographic mirror plane, that plane does not coincide with a mirror plane of the cages themselves. Consequently, the cage is disordered over four superimposed sites.

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The structure of one of the three previously separated isomers of {Er2@C82} has been determined through a single-crystal X-ray structure determination of the noncovalent adduct, {Er2@C82 Isomer I}.{CoII(OEP)}.1.4(C6H6).0.3(CHCl3). The C82 cage is identified specificlly as the Cs(82:6) isomer (one of nine possible isolated pentagon isomers) from the crystallographic data. The carbon atoms of the C82 cage were individually identified and refined with only a constraint that required the two halves of the cage to possess similar bond lengths. Although the carbon cage is well ordered at 113 K, the erbium atoms are disordered. The electron density within the cage of {Er2@C82 Isomer I} has been modeled with two major sites with occupancies of 0.35 and 21 other individual erbium sites with occupancies ranging from 0.138 to 0.011. These erbium sites all reside near the walls of the fullerence and cluster near a band of ten contiguous hexagons that encircles the carbon cage. Since two other isomers of C82 (C3v(82:8) and C2v(82:9)) have a similar band of ten contiguous hexagons, it is tempting to speculate that the other two known isomers of {Er2@C82} have these cage structures.

Heterometallic carboxyphosphonates UO(2)(2+)/Ln(3+) have been prepared from the hydrothermal reaction of uranyl nitrate, lanthanide nitrate (Ln = Sm, Tb, Er, Yb), and phosphonoacetic acid (H(3)PPA). Compound 1, (UO(2))(2)(PPA)(HPPA)(2)Sm(H(2)O)·2H(2)O (1) adopts a two-dimensional structure in which the UO(2)(2+) metal ions bind exclusively to the phosphonate moiety, whereas the Ln(3+) ions are coordinated by both phosphonate and carboxylate functionalities. Luminescence studies of 1 show very bright visible and near-IR samarium(III)-centered emission upon direct excitation of the uranyl moiety. The Sm(3+) emissive state exhibits a double-exponential decay with lifetimes of 67.2 ± 6.5 and 9.0 ± 1.3 μs as measured at 594 nm, after excitation at both 365 and 420 nm. No emission is observed in the region typical of the uranyl cation, indicating that all energy is either transferred to the Sm(3+) center or lost to nonradiative processes. Herein we report the synthesis, crystal structure, and luminescent behavior of 1, as well as those of the isostructural terbium, erbium, and ytterbium analogues.

The electrochemical properties of solid films deposited on an electrode surface by simultaneous electrochemical reduction of C 60 and palladium(II) acetate trimer in an acetonitrile/toluene mixture have been studied using cyclic voltammetry. The electrochemical switching between the doped (conducting) and undoped (nonconducting) states involves both electron and ion transport within the film. The overall control of charge percolation through the C 60 /Pd electroactive material is governed by the transport of cations. The ion transport depends both on the nature of solvent and supporting electrolyte. The size of solvent molecule is the major factor determining the degree of solvent swelling of the layer. In the case of small solvent molecules, the C 60 /Pd film exhibits a reversible redox behavior. For larger molecule solvents, the voltammograms show a departure from reversibility. The reduction of the layer is accompanied by changes in its morphology allowing for the solvent swelling of the film also in the case of large molecule solvents. The electrochemical response of the layer is not affected by the anions of the supporting electrolyte. However, a strong influence of both nature and concentration of supporting electrolyte cations on the redox properties of the layer is observed, since these cations are incorporated into the C 60 /Pd layer. The redox ability in solutions containing large cations is considerably reduced. The activation of the film at negative potentials results in an increase of the doping level. The stability of the films is affected by the potential range over which they are examined. Scanning to highly negative potentials results in the loss of redox activity due to removal of the film from the electrode surface.