Luminescence sensing, lanthanide

Gunnlaugsson, T., Harte, A.J., Leonard, J.R, and Nieuwenhuyzen, M. (2002) Delayed lanthanide luminescence sensing of aromatic carboxylates using heptadentate triamide Tb(III) cyclen complexes the recognition of salicylic acid in water. Chemical Communications, 2134-2135. 

It is clear from the many examples discussed in this chapter that lanthanide lununescent sensors, probes and imaging agents have established themselves as a major player within the field of luminescent sensing. And we can only foresee that the role of these rare-earth ions will continue to grow in the years to come, and that the field of lanthanide luminescence sensing has a very bright and varied future. 

Method A has been successfully applied in anion sensing. As mentioned previously, lanthanide ions can coordinate to anions such as acetate, fluoride, etc., which modulates the lanthanide luminescence. Examples of such systems will now be discussed. 

Cation recognition by luminescence sensing has also been reported. As referred to above, release and recapture of alkali and alkaline earth metal ions for [(bpy)Re(CO)3L ]+, where Lj contains an azacrown ether [63] was controlled by light. A sensor for lanthanide ions is shown in Fig. 27. The photoactive center was RcI( bpy ) and its emission was quenched by the lanthanide ion [119]. 

The spectroscopic characteristics of actinide and lanthanide luminescent probes are sensitive to numerous parameters, such as modifications of solvent composition, addition of supporting electrolytes, temperature changes etc. Therefore, TRES appears as an interesting tool for the chemist, because it provides sensitive experimental data. However, the interactions between the probe and the surrounding medium (in a wide sense) appear to be intricate and difficult to handle. In this sense, attempts to describe lifetime variations as a function of a unique parameter, the hydration sphere number, have shown their limitations. On the other hand, the open questions related to Forster s mechanism are a vivid and still not fully explored field. 

Gunnlaugsson, T. and Leonard, J.R (2005) Responsive lanthanide luminescent cyclen complexes from switching/sensing to supramolecular architectures. Chemical Communications, 3114-3131. 

Massue J, Quinn SJ, Guimlaugsson T (2008) Lanthanide luminescent displacement assays The sensing of phosphate anions using Eu(in)-cyclen-conjugated gold nanoparticles in aqueous solution. J Am Chem Soc 130 6900... 

Sensing Luminescent Probes Based on Near-Infrared Lanthanide Luminescence... 

Luo F, Batten SR (2010) Metal-organic framework (mof) Lanthanide(ni)-doped approach for luminescence modulation and luminescent sensing. Dalton Trans 39 4485... 

Gunnlaugsson T, Leonard JP. Responsive Lanthanide Luminescent Cyclen Complexes from Switching/Sensing to Supramolecular Architectures. Chem Commun 2005 2005 3114-3131. 

Dickins, R. S. Gunnlaugsson, T. Parker, D. Peacock, R. D. Reversible anion binding in aqueous solution at a cationic heptacoordinate lanthanide centre selective bicarbonate sensing by time-delayed luminescence. Chem. Commun. 1998, 16, 1643-1644. 

Another related example is 52 [157], which is a tetra-substituted cyclen ligand with four quinoline receptor moieties capable of sensing protons in a similar manner to 50. The lanthanide emission was found to be switched on in highly acidic conditions, with a luminescent enhancement of over 300-fold. Luminescent enhancement was attributed to an enhancement in the population of the Si and subsequent Ti excited states of the quinoline chromophore when in acidic media. A bell-shaped pH profile was found to exist at pH 1.8-3.5, whereas at more acidic pH the emission was switched off. 

Another possibility is to take advantage of the effect of various supporting electrolytes (in a wide sense) that act as luminescence enhancers, as discussed in sect. 3.3, such as phosphoric acid. This method has been investigated in details both for lanthanides and actinides... 

Anion sensing using visible-emitting lanthanide probes has proven successful (Tsukube et al., 2006) and this work is now being extended to Ybm probes, particularly for the detection of thiocyanate. The latter is the principal metabolite of cyanide anion and exists in human serum, saliva, and urine. The luminescent probe is a complex of hexadentate tetrakis(2-pyridylmethyl)ethylenediamine (tpen, see fig. 119) which bears two water molecules, [Yb(tpen)(H20)2](0tf)3. In absence of anion coordination, the 980-nm luminescence is quenched, but the replacement of the water molecules with thiocyanate or other anions such as acetate, nitrate or halogenides removes the quenching, which makes the complex a responsive probe. The largest effect (a six-fold increase in luminescence) is obtained for thiocyanate, followed by acetate and nitrate (3.5-fold) and chloride (two-fold). 

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