Lanthanide antennae

Poly(ether ketone) dendrons [24] have been observed to show an antenna effect toward lanthanide cations, especially for Eu +. Two focal coordination forms were examined, namely carboxylate [25] and 1,3-diketonate [26]. The use... 

Two practical advantages of luminescence species engulfed in antenna dendrimer scaffolds are apparent, namely their miscibility with organic media (solvents or/and resins) and their ability to form thin films. For example the lanthanide-cored dendrimer complexes described in this chapter can be regarded as organic-soluble inorganic luminescers. 

The sol-gel co-immobilization of a non-fluorescent blue indicator bromothymol blue (BTB) with an europium (Ill)-complex intense antenna mediated lanthanide dye represents a new scheme for the fluorescence analysis38. Luminescence spectra of europium (Ill)-complex shown in Figure 12 were found to be independent of pH changes in the range 1-10. Therefore, BTB, a non-fluorescent pH indicator with alkaline absorption maximum close to main europium emission band was added to the sol-gel mixture to shield reversibly the emission of the europium (Ill)-complex at different pH s without quenching of the antenna function. 

Figure 9.49 Examples of antenna-chelator compounds that have been used for lanthanide luminescence.

Another antenna group that is particularly effective for lanthanide luminescence is carbosty-ril derivatives (7-amino-4-methyl-2(lH)-quinolinone), which can be attached to many chelating... 

Ge, P., and Selvin, P.R. (2004) Carbostyril derivatives as antenna molecules for luminescent lanthanide chelates. Bioconjugate Chem. 15, 1088-1094. 

Kawa, M., and Frechet, J.M.J. (1998) Self-assembled lanthanide-cored dendrimer complexes enhancement of the luminescence properties of lanthanide ions through site-isolation and antenna effects. Chem. Mater. 10, 286-296. 

For protein and DNA studies several methods of locating the lanthanide probe onto the chain have been employed. In one example the antenna fluorophore is covalently attached to one leg of the chelate of europium or terbium, which is further attached to the specific site through thiol reactive, e.g. maleimide, or amine reactive, e.g. A-hydroxysuccinimide, groups. A typical example is shown in (3.77). ... 

An important measure of the luminescence is the quantum yield. In effect, this is the probability that a photon will be emitted by the lanthanide given that one photon has been absorbed by the antenna ligand. Since measurement of absolute quantum yields is particularly difficult, the overall quantum yield ( ) is normally measured with reference to certain standards (26) these are routinely [Ru(bpy)3]2+ in water or SulfoRhodamine 101 in methanol for Eu3 +, and quinoline sulfate in 0.1 M HC1 or fluorescein in 1 N NaOH for Tb3+ (27,28). A method has been developed that measures energy transfer from the lanthanide complex to an acceptor of known quantum yield (28). 

Related complexes where two ligands encapsulate the lanthanide center have been reported (38,39). Coordination of a second antenna ligand may increase the luminescence by excluding deactivating solvent molecules to date, however, photophysical studies for these complexes have not been published. A recent paper details ternary complexes with an additional chromophore, antipyrene (antipy)... 

A number of aromatic groups are known to intercalate DNA. Among these are tetraazatriphenylenes, which have been shown to bind to the minor groove of DNA. These functional groups have been incorporated into a luminescent lanthanide complex (71), where it serves not only to bind to DNA, but also acts as the antenna ligand. As a consequence of this, intercalation prevents luminescence by quenching the ligand excited state (194). 

Alpha, B. Ballardini, R. Balzani, V. Lehn, J.-M. Perathoner, S. Sabbatini, N. Antenna effect in luminescent lanthanide cryptates a photophysical study. Photochem. Photobiol. 1990, 52(2), 299—306. 

Shavaleev, N. M., Moorcraft, L. P., Pope, S. J. A., Bell, Z. R., Faulkner, S., Ward, M. D., Sensitised near-infrared emission from lanthanides using a covalently-attached Pt(U) fragment as an antenna group. Chem. Commun. 2003, 1134-1135. 

The sensitisation process associated with producing lanthanide luminescence consists of a number of steps, including excitation of the antenna and energy transfer to the lanthanide. The details of this process and the considerations required in designing complexes working on this principle are discussed in the following sections. 

Fig-1 Illustration of energy transfer to the lanthanide ion in sensitisation process for Tb(III), from triplet state of the antenna and the corresponding emission spectra for Tb(III)... 

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