Rare-earth chelates, energy transfer

Rare-earth chelates, energy transfer, 203 Rare-earth, energy levels of, 25 Recombination luminescence, 160 Redox potential excited state, 111 of PS I and PS II, 282 Redox reactions, 218... 

Figure 6.16 Energy transfer pathway in rare earth chelates.

Hemingway RE, Park S-M, Bard AJ. Electrogenerated chemiluminescence. XXL Energy transfer from an exciplex to a rare earth chelate. J Am Chem Soc 1975 97 200-1. 

A series of papers report the electrogenerated chemiluminescence in laser cavities,310-318 and electrogenerated chemiluminescence systems with energy transfer to some rare-earth chelates have been examined.819 287 288... 

Similar examples for energy transfer from ligand localized levels to highly localized 4f levels are represented by the rare-earth chelates. Voloshin and Savutskii (1976) studied europium benzoylacetonate imder pressures up to 6 GPa. Exciting the triplet level they could observe the luminescence from the Eu " " ion. It was possible to describe the observed initial increase in the quantum yield of the Eu " " luminescence up to 2.5 GPa and the following decrease by the exchange resonance theory (Dexter, 1953). A more detailed study on different Tris chelates of Sm +, Eu +, Gd " ", and Tb " with -diketonates was performed by Hayes and Drickamer (1982), where the most dramatic effects of pressure on energy transfer phenomena were found for the Eu + chelates. 

Sato, S. Wada, M. Relations between intramolecular energy transfer efliciences and triplet energies in rare earth beta-diketone chelates. Bull. Chem. Soc. Japan 1970, 43,1955. 

A study has been made of the relative efficiencies with which various transition metal chelates quench triplet benzophenone.194 The chelates vary widely in efficiency, and no generalizations can be drawn except that in some cases triplet energy transfer to a coupled metal-ligand triplet energy level probably accounts for at least part of the quenching. Rare earth ions can quench excited triplets by energy transfer, since, as discussed earlier, sensitized fluorescence of the metal ion results. 

Salicylates.—In the course of his intramolecular energy transfer studies (p. 130) on europium chelates Weissman 630 prepared the 3-nitro and 5-nitro salicylate complexes. He was one of the first to demonstrate the phenomena of intramolecular energy transfer (IMET) from the coordinated ligands to the central rare earth ions giving characteristic fluorescence of the metal ions. However, no analytical data on these compounds are available. 

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... 

In n-butanol as solvent at 293 K Tb(acac)3-3H20 undergoes intermolecular energy transfer to the complexes R(acac)3-3H20 (R = Pr, Nd, Sm, Eu, Dy, Ho, or Er) (Napier et al., 1975). Measurement of the decay time of the D4 level of the terbium(III) ion indicates that transfer takes place from that level to the excited levels of the other rare earths with bimolecular rate constants of 0.5-4.9x lO dm mol s. The fluorescence lifetime for the D4 state of terbium in gaseous Tb(DPM)3 has also been determined. These measurements have been made by Jacobs et al. (1975) as a function of temperature and pressure and the results demonstrate that intermolecular collisional deactivation is not important. Rather, the non-radiative deactivation is an intramolecular process and occurs by means of a transfer to low-lying excited states of the chelate. The fluorescence decay time is 1 s at 200°C which is very much shorter than those observed in 95% ethanol ( 600 /ts) and in the solid state (—500 fis) at room temperature. 

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