Fluorescence of rare earth complexes

Influence of P-diketone ligand on fluorescence of rare earth complex in LB film.160... 

The influence factors on fluorescence of rare earth complexes are very complicated, including ligand structure, matching between energy levels, thermal non-radiative deactivation, temperature, solvent and rare earth ions as discussed in Section 3.3. In this section, we only briefly discuss our results focusing on two factors. First, the ligand structure plays an important... 

Fluorescence Properties of Rare Earth Complexes Containing 1,8-Naphthyridines... 

Table 2 Fluorescence result of rare earth complexes in mixed 18-layer LB films with AA in a molar ratio of 1 1...

Varying the p-diketone ligands binding a given rare earth ion, the fluorescence intensity of rare earth complexes in LB film decreased in the following order ... 

The fluorescence intensity of rare earth complexes in LB film has the same decrease sequence as that in solution. In other words, in Eu(III) or Sm(III) complexes, the complex with the p-diketone TTA emits the most intense fluorescence in LB film. However, terbium complex with acac emits the most intense fluorescence in Tb(IlI) complexes. 

The above results show that, fluorescence from rare earth complexes can be further altered by certain molecules in adjacent layer of LB films, which is helpful for their future application in luminescence devices involving fluorescence modulation. 

Kropp J.L., Windsor M.W. Luminescence and energy transfe in solutions of rare-earth complexes. I. Enhancement of fluorescence by deuterium substitution. J. Chem. Phys. 1965 42 1599-1608... 

The X-ray determination of REE in geological samples is normally complicated by the relatively low concentrations of the REE, their complex X-ray spectra, the high concentration of matrix elements and the lack of reference standards with certified values for REE. A rapid and sensitive ion exchange and X-ray fluorescence procedure for the determination of trace quantities of rare earths is described. The REE in two U.S.G.S. standards, two inhouse synthetic mixtures and three new Japanese standards have been determined and corrections for inter-rare earth element interferences are made. 

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... 

The first two chapters of this book are devoted to the historical and mineralogical aspects of rare earths followed by seperation techniques. It is obvious that these two chapters cannot be limited only to the discussion of europium. Hence, the whole of the rare earth family has been treated with especial emphasis towards europium. Chapters three to five describe exclusively the chemical behaviour of europium and also the interesting features of its complexes and alloys. However, where necessary, mention of other rare earths has been made. The spectroscopic properties, both absorption and fluorescence, are dealt with in chapter six, which is followed by an account of the possible uses of europium in the last chapter. 

To be successfully used as labels in biological assays, rare earth complexes should possess specific properties including stability, high light yield, and ability to be linked to biomolecules. Moreover, insensitivity to fluorescence quenching is of crucial importance when working directly in biological fluids. When complexed with cryptates, however, many of these limitations are eliminated. 

Some lanthanide ions when complexed with UV-absorbing ligands, can efficiently accept energy from the excited state of the ligand and produce highly enhanced emission characteristics of the metal ion. Rare earth complexes have some advantages over organic fluorescent probes such as fluorescein, rhodamines, umbelliferones such as... 

New luminescent hybrid mesoporous material was prepared by covalent anchoring rare earth complex onto MCM-41 by a postsynthesis approach. The monomer (referred to here as PABI) which plays double roles, i.e., as a ligand for lanthanide ion and as an organic functional molecule to modify MCM-41 is synthesized and characterized by H NMR and MS. The fluorescence spectra show clearly that the hybrid mesoporous material possesses excellent luminescence characteristics. The hybrid mesoporous material retains the structure of MCM-41 after modification. 

Research is going on to improve the DELFIA system , because of drawbacks such as the time-consuming conversion of the non-fluorescent RE label into a luminescent complex, or the system vulnerability to contamination by RE due to the excess of the reagents ntfa and topo. An alternative is the use of a -diketone that can be covalently bonded to proteins such as 5-(4,4,4-trifluoro-l,3-dioxobutyl)-2-thiophenesulfonyl chloride (ctta) . Since the stability of the RE + complexes formed by this ligand is quite low, a large excess of RE + has to be used to shift the equilibrium to the rare-earth complex. More stable europium complexes can be obtained by the use of tetradentate fi-diketonates, such as 7a-7d, anchored on a functionalized o-terphenyl skeleton, or 8a-8c, anchored on a biperfluorobutadiene skeleton . ... 

Ligand labeling with fluorescent metal chelates has created a versatile class of fluorescent probes. The chelates of rare earth metals have unique emission characteristics in that, upon excitation of aromatic portions of the ligands of the lanthanide complex, the energy of excitation is efficiently transferred to the lanthanide ion. This causes f-f transitions that produce very narrow almost line-like emission bands that permit all of the emitted light to be collected by the detector with narrow emission slits. In addition, the rare earth... 

On a qualitative basis, the fluorescence of the napy complexes containing chloride is weaker than that of the corresponding nitrate compounds. Such variation can be ascribed to the difference in coordinating ability of the anion and/or to the amount of coordinated water. Conductivity studies of the nitiate and chloride complexes in nitromethane yield A values of 13-19, which indicates that the complexes are nonelectrolytes (12, 13, 14). The presence of bands attributable to vM-Cl and vM-OH ) in the IR spectra of the chloride complexes substantiates the conclusion that all species are bound to the rare earth ion (12), Vibrational modes indicative of bidentate nitrate and the lack of bands suggesting monodentate nitrate are reported for the rare earth nitrate complexes of napy and 2,7-dmnapy (13,14),... 

For 2,7-dmnapy complexes of the same rare earth, the recorded intensities of the nitrate complexes are always greater than those in which acac is the anion. Conductivity measurements on nitromethane solutions of M(acac)3(2,7-dmnapy) give A values of 6-9 which are typical of nonelectrolytes (II, 12). IR spectra of the acac complexes have vCO absorptions at approximately 1600 and 915 cm" and i/M-0 bands at 405 and 313 cm" These absorptions and the lack of a 1700-cm band indicate that both oxygens of each of the acac units are coordinated to the metal (II, 30). The more intense fluorescence of the nitrate complex may result from the presence of a second 2,7-dmnapy ligand which would increase the coordination number of the rare earth from 8 to 10. The triplet state of acac is reported at 25,300 cm (31). The triplet state of napy at 22,210 cm" is closer to the rare earth resonance levels and may contribute to a more efficient energy transfer which in turn would enhance fluorescence intensity. 

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