Internal-Energy-Transfer Efficiencies in Eu3+ and Tb3+ Chelates Using Excitation to Selected Ion Levels

Abstract

Fluorescence yields of solutions of several chelates of europium and terbium have been measured: (a) upon excitation in the ligand absorption bands and (b) upon selective excitation to individual upper levels of the rare-earth ion. Yields with upper-ion-level excitation are lower than when the emitting level is excited directly and yields with ligand excitation are lower still. Efficiencies of energy transfer to the emitting level from upper ion levels and from the ligands, for the solutions studied, are calculated from the data. The fluorescence yield observed when the emitting level is excited directly, together with the fluorescence lifetime, allows both radiative and radiationless rate constants for deactivation of the emitting level to be calculated. The enhanced fluorescence yields of chelates compared to unchelated rare-earth ions are found to be due primarily to the enhancement of the radiative transition by the chelate environment rather than to a protective influence against quenching provided by the ligands. For terbium chelates the strong temperature dependence of the fluorescence intensity is explained in terms of quenching of the emitting level via thermal excitation to the lowest triplet state of the ligand. This is indicated by the agreement between the activation energy for quenching and the energy difference between the emitting level and the triplet state.

Direct Kinetic Evidence for Triplet State Energy Transfer from Escherichia coli Alkaline Phosphatase Tryptophan 109 to Bound Terbium

“…The observation of increased terbium luminescence following deoxygenation of terbium containing samples of synthetic peptides (4) and several calciumbinding proteins (11) provides strong evidence that protein triplet states may be involved. Indeed, for nonbiological systems the involvement of aromatic triplet states as donors has long been known (12)(13)(14)(15). A recent detailed investigation (16) has considered the mechanisms of dipole-dipole, electron exchange, superexchange, external heavy atom effect, and electron transfer in the interpretation of fluorescence quenching of one to one lanthanide complexes of an indolyl-EDTA 1 derivative where the metal ion is held in a cofacial geometry about 6 Å from the center of the indole ring.…”

Spectral, Electrochemical, Fluorescence, Kinetic and Anti-microbial Studies of Acyclic Schiff-base Gadolinium(III) Complexes

“…In the intramolecular energy transfer, triplet state energy of the ligand is regarded as an important factor in excitation of the lanthanide ion. 21,22 Comparing with this mononuclear…”

Spectral, Magnetic, Electrochemical, Photochemical, DNA Binding and Cleavage, Catalytic and Biological Studies of 2, 2'-Bipyridyl Based d-f Hetero Binuclear Gd(III) and Cu(II) Complexes

“…The luminescence of Ln 3+ chelates is related to the efficiency of the intramolecular energy transfer between the triplet levels of the ligand and the emitting level of the ions, which depends on the energy gap between the two levels. In the intramolecular energy transfer, triplet state energy of the ligand is regarded as an important factor in excitation of the lanthanide ion 18,19 . Compared with complex 3 [GdCuL 3 ], there is lower emission band in the range 400-700 nm indicating the fluorescence of Gd, Cu ion in the cavity was completely quenched [20][21][22] , which is magnetic-dipole allowed, is hardly affected by a change of the coordination environment.…”