Photophysics lanthanide ions

Chauvin, A.S., Gumy, R, Matsubayashi, I., etal. (2006) Fluorinated fl-diketones for the extraction of lanthanide ions photophysical properties and hydration numbers of their Eu " complexes. European Journal of Inorganic... 

Luminescent lanthanide ions have numerous practical applications in chemistry and technical devices, some of them involving electrical excitation of the lanthanide ions. Photophysical properties of lanthanide ions as well as perhaps the most important application field, photoluminescence of lanthanide chelates, and lanthanide-containing nanoparticles are treated elsewhere in this volume. 

The photophysical properties of lanthanide ions are influenced by their local environment, the nature of the quenching pathways available to the excited states of sensitizing chromophores, and the presence of any available quenchers (as we have seen when discussing bioassay). All of these factors can be exploited for the sensing of external species. 

For some recent reviews, see (a) Leonard JP, Nolan CB, Stomeo F et al (2007) Photochemistry and photophysics of coordination compounds lanthanides. Top Curr Chem 281 1-43 (b) Biinzli J-CG, Piguet C (2005) Taking advantage of luminescent lanthanide ions. Chem Soc Rev 34 1048-1077 (c) Parker D (2000) Luminescent lanthanide sensors for pH, p02 and selected anions. Coord Chem Rev 205 109-130... 

The parent ligand tris(pyrazolyl)borate, [L4]-, forms 1 1 and 1 2 metakligand complexes [Ln(L4)(N03)2] and [Ln(L4)2]+ the molecular structure of the latter is shown in Fig. 6. In solution, dissociation of the nitrate anions in the former complex leave the lanthanide ion open to coordination by solvent molecules (47). Photophysical studies in water and methanol (48) confirm this use of the Horrocks equation... 

Photophysics of near-infrared emitting trivalent lanthanide ions... 

Because of the higher sensitivity of Ndm ions towards deactivation through O-H oscillators, the complexes with this lanthanide have much lower quantum yields and lifetimes when compared to Ybm. The best photophysical properties are obtained with phthalexon S and since complexes with PS contain 4-5 water molecules, depending on the lanthanide ion, it is quite clear that exclusion of these water molecules from the first coordination sphere will lead to much enhanced luminescent properties. This is indeed demonstrated by bis(cyclen)-substituted PS, H736 (see fig. 36), which increases quantum yields to 0.23 and 1.45% in D2O for Ndm and Ybm, respectively (Korovin and Rusakova, 2002). 

Disregarding this aspect, and since cyclam is an interesting core for constructing den-drimers because it can be easily functionalized and because despite its absence of spectroscopic properties, it can interact in such a way with dendrons as to modify their photophysical properties, the interaction of lanthanide ions with cy clam-based dendrimers has been investigated. The dendrimers are constmcted from the cyclam core fitted with four dimethoxyben-zene and eight naphthyl units (generation 1, fig. 81) second generation introduces a total of 12 dimethoxybenzene and 16 naphthyl moieties. Coordination to Lnm ions occurs in acetoni-trile/methylene chloride (Ln = Nd, Eu, Gd, Tb, and Dy), but no sensitized Ln-luminescence was observed (Saudan et al., 2004). Another example of a macrocycle-based dendrimer is discussed below in section 3.3.2. 

Contents J.A.Ibers, L.J.Pace, J.Martinsen, B.M.Hoffman Stacked Metal Complexes Structures and Properties. -M.J. Clarke, P.H.Fackler The Chemistry of Technetium Toward Improved Diagnostic Agents. - R.J.P. Williams The Chemistry of Lanthanide Ions in Solution and in Biological Systems. - C.K. Jorgensen, R.Reisfeld Uranyl Photophysics. 

Wolbers, M.RO., van Veggel, F.C.J.M., SnelUnk-Ruel, B.H.M., et al. (1998) Photophysical studies of m-terphenyl-sensitized visible and near-infrared emission from organic 1 1 lanthanide ion complexes in methanol solutions. Journal of the Chemical Society, Perkin Transactions, 2, 2141. 

Figure 13.4 Typical design principle of lanthanide complex-based chemosensors based on binding of an analyte (an) (a) directly influencing the Ln(III) luminescence, (b) influencing photophysical properties of the ligand, and (c) addition of a sensitizing analyte onto a poorly luminescent lanthanide-containing sensor [1]. (Reproduced from J.C.G. Bunzli and C. Piguet, Taking advantage of luminescent lanthanide ions, Chemical Society Reviews, 34, 1048-1077, 2005, by permission of The Royal Society of Chemistry.)...

Applications of photophysics in biology and medicine are very extensive and only a few topics can be mentioned in this review. A survey of the use of lanthanide ions as luminescent probes of biomolecular structure and a general account of long distance electron transfer in proteins and model systems are very helpful. The methods applicable to the synthesis and activation of a number of photoactivable fluoroprobes have been described and photoactivation yields measured . 

For phosphorescence, lanthanide metal ions can be used in a similar manner. Lanthanide ions have very interesting photophysical properties, but often exhibit weak absorption bands, and aggregate to form clusters, which limit their applications. Thus, a dendrimer that can provide a protective shell to isolate a cation and at the same time enhance the emission by transfer from the periphery to the lanthanide ion at the core could be of great interest. Self-assembled lanthanide-cored dendrimers have been prepared to prove such an assumption synthesis was carried out by mixing three equivalents of polyaryl ether dendrons bearing carboxylic acid entity at the focal point with Ln(III) cations [Er(III), Tb(III), and Eu(III)] (Fig. 5.4) [34]. The authors demonstrated that the enhancement of the lanthanide cation emission associated with the dendritic core shell was observed, and an antenna effect from the periphery to the core was shown to promote this process. 

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