Luminescent ternary complex

The detection of aromatic carboxylates via the formation of ternary complexes using lanthanide ion complexes of functionalised diaza-crown ethers 30 and 31 has been demonstrated [134]. Like the previous examples, these complexes contained vacant coordination sites but the use of carboxylic acid arms resulted in overall cationic 2+ or 1+ complexes. Furthermore, the formation of luminescent ternary complexes was possible with both Tb(III) and Eu(III). A number of antennae were tested including picolinate, phthalate benzoate and dibenzoylmethide. The formations of these ternary complexes were studied by both luminescence and mass spectroscopy. In the case of Eu-30 and Tb-30, the 1 1 ternary complexes were identified. When the Tb(III) and Eu(III) complexes of 30 were titrated with picolinic acid, luminescent enhancements of 250- and 170-fold, respectively, were recorded. The higher values obtained for Tb(III) was explained because there was a better match between the triplet energy of the antenna and a charge transfer deactivation pathway compared to the Eu(III) complex. 

Fig. 1. Binding of an analyte to a lanthanide-based receptor produces a luminescent ternary complex. The ancillary (receptor or helper) ligand is shown in dark gray.

Pope, S.J.A., Burton-Pye, B.P., Berridge, R., et al. (2006) Self-assembly of luminescent ternary complexes between seven-coordinate lanthanide(lll) complexes and chromophore bearing carboxylates and phosphonates. Dalton Transactions, 2907. 

Leonard et al. prepared a luminescent ternary complex from ligand 55b, Eu " cation, and an aromatic j0-diketonate anion [136]. Addition of F , acetate, HCOa", and tartarate anions gave gradual luminescence changes at... 

The above examples demonstrate how simple anions such as halides, carboxylates and carbonates can bind direcdy to the lanthanide centres and concomitantly modulate the photophysical output of such complexes. In a similar manner, aryl-based anions can be employed, and the formation of luminescent ternary complexes can thus be achieved. Both Gunnlaugsson et al. [69] and Faulkner et al. [70] have demonstrated, for instance, that simple anionic antennas can be bound to Tb and Yb cyclen complexes (Scheme6.14a, b, c). The former two Tb examples (Scheme 6.14a, b) are based on the use of cationic complexes. 

The opportunity of use of a ternary complex of ions Eu(III) with oxatetracycline (OxTC) and citrat-ions (Cit) for luminescent detection of OxTC in milk after chromatographic isolation is shown. 

We detenuined the influence of oxy- and ketocarboxylic acids (succinate, fumarate, adipinate, a-ketoglutarate, isocitrate, tartrate, E-malate) on the luminescence intensity of the Eu-OxTc complex. These substances interact as polydentate ligands similarly to citrate with the formation of ternary complexes with Eu-OxTc. As to succinate, fumarate, adipinate and a-ketoglutarate this they cannot effectively coordinate with EiT+ and significant fluorescence enhancement was not observed. 

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)... 

The formation of these ternary luminescent lanthanide complexes was the result of displacement of the two labile metal-bound water molecules, which was necessary because the energy transfer process between the antenna and the Ln(III) metal centre is distance-dependent. This ternary complex formation was confirmed by analysis of the emission lifetimes in the presence of DMABA and showed the water molecules were displaced by a change in the hydration state q from 2 to 0, with binding constants of log fCa = 5.0. The Eu(III) complexes were not modulated in either water or buffered solutions at pH 7.4. Lifetime analysis of these complexes showed that the metal-bound water molecules had not been displaced and that the ternary complex was not formed. Of greater significance, both Tb -27 and Tb -28 could selectively detect salicylic acid while aspirin was not detected in buffered solutions at pH 7.4, using the principle as discussed for DMABA where excitation of the binding antenna resulted in a luminescent emission upon coordination of salicylic acid to the complex. 

Luminescence properties of Eu(III) 3-diketonate ternary complexes with TOPO in benzene.3 Refer to scheme 4 for... 

The EDTA-Tb3+ complex is poorly luminescent, but becomes strongly emissive when it forms a ternary complex with salicylic acid. By using alkaliphosphatase (ALP) as the label of the antibody, a unique immunoassay system specific to Tb3+ was constmcted (fig. 11) by Evangelista et al. (1991) and Christopoulos et al. (1992). The enzyme ALP cleaves the phosphoester bond of the substrate and releases 5-fluorosalicylic acid, which binds to EDTA-Tb3+ and sensitizes luminescence from Tb3+. This method is employed for the determination of semm AFP (cx-fetoprotein) and PSA (prostate-specific antigen). 

Instead of grafting a coordinating chromophore on the macrocyclic framework, which sometimes requires the recourse to relatively comphcated synthetic routes, another strategy was tested, which forms ternary complexes in situ. An example is pyrene acetic acid H34 (fig. 35) which reacts with [Ln(26d)(H20)2] to form kinetically labile ternary complexes [Ln(26d)(34)(H20)x], Ln = Nd, Yb (Faulkner et al., 2004). Metal-centered luminescence occurs upon pyrene excitation. However, according to lifetime measurements for Yb111, 0.72 and 2.52 ps in H2O and D2O, respectively, and the use of eq. (9a), q = 0.9, which suggests that a pyrene acetic acid molecule is coordinated to the metal center expelling one water molecule, but not the second one. That is, the ternary complex does not represent an improvement over [Yb(30a)]. 

Right) Luminescence lifetimes of tris and ternary Nd111 complexes as a function of the fluorinated radical chain length. Filled and opened triangles stand for tris complexes with benzoylacetonate and thienylacetonate derivatives, respectively filled and opened circles for the corresponding ternary complexes formed with phen. 

Fig. 45. Enhancement factors of the luminescence intensity between some tris(/i-diketonates) and their corresponding ternary complexes.

Strong erbium luminescence with a full-width at half-maximum of 100 nm is also generated by the ternary complex [Er(pos)3phen] upon excitation in the ancillary ligand band at 333 nm. With respect to direct Er111 excitation into the 2Hn/2 level at 520 nm, the photoluminescence signal increases by a factor 20 (Van Deun et al., 2004b). 

X 109 and 8. 9 x 109 s 1 for Ndm and Ybm, respectively. Both the above-described in-termolecular mechanism, as well as an intramolecular pathway in the ternary complex with aad which forms in solution, are responsible for the observation of NIR luminescence in these systems. Addition of water to the toluene solutions quenches the NIR luminescence, while it enhances the visible CL emission of the corresponding solution of Eum and Tbm (Voloshin et al., 2000c). Neodymium and ytterbium tris(benzoyltrifluoroacetonates) display the same CL as tta complexes, although for Ybm its intensity is about 2.5 times lower than for the tta chelate. On the other hand, almost no CL is detected for acetylacetonate complexes (Voloshin et al., 2000a). Thermal or photochemical decomposition of aad also triggers CL from [Pr(dpm)3] and Pr(fod)3], both in the visible (from the 3Pi, 3Po, and 1D2 levels) and in the NIR at 850 nm ( Do -> 3F2 transition) and 1100 nm ( D2 3F4 transition). The excited... 

Another completely different approach consists in choosing a dye, that already possesses aminocarboxylate functions (Meshkova et al., 1992a), such as triphenylmethane dyes. The latter can be used for selective luminescent determination of Nd111 and Ybm in samarium oxide, for instance. As previously described in the section devoted to /3-diketonates (section 3.2.1), the triplet excited states of /i-dikctonatcs lie at energies >20 000-25 000 cm-1, above most of the accepting levels of Lnm ions. As a consequence, determination of Ndm and Yb111 in europium or samarium oxides is difficult using /3-dike to nates since these two ions exhibit luminescence in the NIR, especially Smm with emission lines at 908, 930, 950, and 1038 nm close to the analytical lines of Ndm and Ybm. Therefore, the detection limit of Ndm and Ybm in samarium compounds by luminescence of their ternary complexes with tta and phen is only 0.1-1 wt%. 

The luminescence characteristics of four complexes formed with arsenazo (I and II) and thorin (I and II) dyes (fig. 67) as well as those of the corresponding ternary complexes with phen have been investigated in aqueous solution. In presence of Ybm ions, 1 1 complexes are formed, except for thorin I, which yields a 1 2 (Yb L) complex. As a consequence, for thorin I only one phen molecule is present, yielding a 1 2 1 (Yb L phen) ternary complex, while 1 1 2 stoichiometries are observed for the three other complexes. Addition of phen results in a significant enhancement (2- to 7-fold) of the luminescence quantum yields, which reach a maximum value of 0.13% for the complex with arsenazo I. As a consequence, the detection limits are lowered by similar factors, from 2 to 8. 

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