Lanthanide complexes metal luminescence efficiency

Furthermore, lanthanides form stable complexes with polydentate chelators like DTPA, which exhibit a noncyclic structure. Two structures are depicted in Scheme 2. The following examples are only representatives for the variety of analyte molecules that can be determined by these kind of lanthanide complexes. Structure 9 employs a quinolyl ligand both as chromophore and acceptor for Zn ". The emission of the europium ion is strongly enhanced upon binding of Zn " and showing distinct selectivity over other biologically relevant metal cations in aqueous solution at neutral pH [29]. The luminescence of the chelate 10 is efficiently quenched by Cu " ions in aqueous medium [30]. The presence of Fe ", Co ", Ni ", Cr ", and Mn " interferes with the determination of Cu, although to a relatively small extent, whereas the ions Zn ", Cd ", Hg, and Pb do not interact with probe 10. 

Mameri et al. developed acyclic ligand 51 containing bipyridine carboxylic moieties, which gave high stabihty and hydrophihcity of the lanthanide complex [131]. This formed luminescent 1 1 complexes with Eu " and Tb cations, where two water molecules located in the first coordination sphere of the lanthanide centers. The efficient ligand-to-metal energy transfer was ensured by the bipyridine photoantenna. Upon addition of ATP anion, the Eu luminescence intensity decreased to 20% of its initial value. Since the luminescence lifetime increased from 0.28 to 0.58 and 0.65 ms with the addition of 10 and 20 equivalents of ATP anion, the two boimd water molecules were replaced by the external ATP anion. In contrast, ADP, AMP, and NOs an-... 

Sabbatini et al. 1993). An efficient antenna is expected to lead to metal luminescence much more intense than that obtained upon metal excitation since lanthanide ions are characterized by very low molar absorption coefficients. These complexes can be considered light-conversion molecular devices because they are able to transform light absorbed by the ligand into light emitted by the ions via an intramolecular energy transfer (Balzani and Scandola 1991). 

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