Complexes rare-earth

Metal-centered emission is found in several rare-earth complexes, for example europium diketone chelates [29]. These compounds emit relatively narrow spectra associated with the d-f transitions of the metal ion. Relatively few comprehensive studies of this class have been carried out to date, but the available evidence [30] seems to indicate that the photoluminescent efficiencies are somewhat lower than the ligand-centered emitters. 

Rare earth complexes with neutral macrocyclic ligands. J. C. G. Bunzli and D. Wessner, Coord. Chem. Rev., 1984,60,191 (186). 

Keywords chiral lanthanoid complexes, rare earth complexes, carbocyclic ring construction via intramolecular Diels-Alder reaction... 

Associated to copper(II) pre-catalysts, bis(oxazolines) also allowed the asymmetric Diels-Alder and hetero Diels-Alder transformations to be achieved in nearly quantitative yield and high diastereo- and enantioselectivities. Optically active sulfoximines, with their nitrogen-coordinating site located at close proximity to the stereogenic sulfur atom, have also proven their efficiency as copper ligands for these asymmetric cycloadditions. Other precursors for this Lewis acid-catalyzed transformation have been described (e.g., zinc salts, ruthenium derivatives, or rare earth complexes) which, when associated to bis(oxazolines), pyridine-oxazolines or pyridine-bis(oxazolines), led to efficient catalysts. 

Several groups have reported the use of rare earth complexes as catalysts for asymmetric Diels-Alder reaction. Qian and Wang described thus the preparation and use of Yb complexes chelated by Pr-PyBOx to successfully achieve the hetero-Diels-Alder reaction of methyl glyoxylate with Danishefsky s diene in 77% ee and 73% yield (Scheme 37) [98]. 

Our preliminary attempts to obtain a basic chiral rare earth complex have led us to create several new chiral heterobimetallic complexes which catalyze various types of asymmetric reactions. The rare earth-alkali metal-tris(l,f-bi-2-naphthoxide) complexes (LnMB, where Ln = rare earth, M = alkali metal, and B = l,l -bi-2-naphthoxide) have been efficiently synthesized from the corresponding metal chloride and/or alkoxide,13,41 and the structures of the LnMB complexes have been unequivocally... 

Q.D. Ling, E.T. Kang, K.G. Neoh, and W. Huang, Synthesis and nearly monochromatic photoluminescence properties of conjugated copolymers containing fluorene and rare earth complexes, Macromolecules, 36 6995-7003, 2003. 

It is well-known that rare-earth complexes such as europium complexes emit sharp spectral bands due to electronic transitions between inner d and f orbitals of the central rare-earth... 

A further strategy to achieve white emission uses rare-earth complexes. For example, a dysprosium complex (245) emits two band emissions a yellow band (580 nm) corresponding to the 4F9/2 —> 6Hi3/2 transition and a blue band (480 nm) corresponding to 4F9/2 — 6H15/2 transition of Dy3+ ion in the complex. Li et al. reported Dy-complex white emission OLEDs of a structure of ITO/PVK Dy complex/Mg Ag device [276], Figure 3.13 shows the PL and EL emission spectra of such a complex and its device, respectively. 

Trigonal ML3 metal complexes exist as optically active pairs. The complexes can show enantiomeric selective binding to DNA and in excited state quenching.<34) One of the optically active enantiomers of RuLj complexes binds more strongly to chiral DNA than does the other enantiomer. In luminescence quenching of racemic mixtures of rare earth complexes, resolved ML3 complexes stereoselectively quench one of the rare earth species over the other. 35-39 Such chiral recognition promises to be a useful fundamental and practical tool in spectroscopy and biochemistry. 

Edelmann, F.T. Rare Earth Complexes with Heteroallylic Ligands. 179, 113-148 (1996). 

Recently, rare-earth metal complexes have attracted considerable attention as initiators for the preparation of PLA via ROP of lactides, and promising results were reported in most cases [94—100]. Group 3 members (e.g. scandium, yttrium) and lanthanides such as lutetium, ytterbium, and samarium have been frequently used to develop catalysts for the ROP of lactide. The principal objectives of applying rare-earth complexes as initiators for the preparation of PLAs were to investigate (1) how the spectator ligands would affect the polymerization dynamics (i.e., reaction kinetics, polymer composition, etc.), and (2) the relative catalytic efficiency of lanthanide(II) and (III) towards ROPs. 

Fig. 29 Rare-earth complexes with heteroselective rac-lactide ROP...

Edelmann FT (1996) Rare Earth Complexes with Heteroallylic Ligands. 179 113-148 Edelmann FT (1996) Lanthanide Metdlocenes in Homogeneous Catalysis, 179 247-276 Ekhart CW, see de Raadt A (1997) 187 157-186... 

Kropp and Windsor (105,107) studied extensively the effects of deutera-tion on the luminescence characteristics of some rare-earth complexes. Solutions of europium and terbium salts in heavy water give fluorescence intensities and lifetimes many times greater than the corresponding solutions in ordinary water. Table X gives the results of their studies on europium... 

Tricyclopentadienyl rare earth complexes ([M(7j5-CSH5)3] M = Er, Nd, Pr, Yb) have been measured by DFWM at a fundamental frequency corresponding to A = 1064 nm.29 They possess moderate nonlinearities despite having electronic transitions in the range 800-1550 nm, which might have been expected to result in dispersively enhanced values. Solution / ul for [Yb(T75-C5H5)3] [the largest nonlinearity of the series, and the complex with Amax (1030 nm) closest to ] is only about half that of CS2. 

Third-Order NLO Measurements of Other Metallocene Complexes and Tricyclopentadienyl Rare Earth Complexes... 

The following steps sum up the basic mechanism of the IMET process as involved in rare earth complexes. 

Fillpescu et al. [556], and Schmitschek and Schwarz [657] in 1962 were the first to point out the possibility of using the rare earth complexes as laser materials due to the low pump power necessary to excite these complexes via the IMET process and the relatively high quantum yield. The diminished lattice coupling of the rare earth ions in complexes may be very important in the liquid laser where quenching is quite serious. 

The first reported laser action in rare earth complexes was obtained by Lempicki and Samelson [656] for europium benzoylacetonate in alcoholic solution. The laser parameters for this complex have also been evaluated by Lempicki and coworkers [656, 660] who found a slightly better quantum efficiency (0.8) for europium benzoylacetonate than for ruby (0.7), the solid state laser. The laser action of europium benzoylacetonate has also been investigated by Schimitschek [661] and Bhatjmik et al. [662]. Some other complexes of Eu3+ viz. dibenzoylmethide [665,664], m-4,4,4-trifluoro-l(2-thienyl)-l,3-butanedione [665], thenoyl-trifluoroacetonate [666, 667] were also found to lase. 

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