Lanthanide complexes encapsulated ions

Calix[ ]arenes are a family of macrocycles prepared by condensation reactions between n /v/ra-substituted phenols and n formaldehyde molecules under either base or acid catalysis. Different sizes of the macrocycles can be obtained (n = 4-20) (Stewart and Gutsche, 1999) depending on the exact experimental conditions, which were mastered in the 1960 s (Gutsche, 1998), but the most common receptors are those with n =4,6,8 (macrocycles with an odd number of phenol units are more difficult to synthesize). We use here the simplified nomenclature in which the number of phenolic units is indicated between square brackets and para substituents are listed first.4 Calixarenes, which can be easily derivatized both on the para positions of the phenolic units and on the hydroxyl groups, have been primarily developed for catalytic processes and as biomimics, but it was soon realized that they can also easily encapsulate metal ions and the first complexes with d-transition metal ions were isolated in the mid-1980 s (Olmstead et al., 1985). Jack Harrowfield characterized the first lanthanide complex with a calixarene in 1987, a bimetallic europium complex with p-terf-butylcalix[8]arene (Furphy etal., 1987). 

This chapter shows that research in the field of lanthanide-based NIR-luminescent materials is very active. In general, incorporation of a lanthanide complex into a matrix significantly improves its thermal and (photo)chemical stability. This can partially be explained by the shielding of the lanthanide complex from the atmosphere and especially from atmospheric oxygen and moisture. The encapsulation of the lanthanide complex in the hybrid matrix often leads to a more intense PL because of light absorption by the host matrix and snbsequent transfer of the excitation energy to the lanthanide complex and finally to the emitting lanthanide ion. 

Encapsulation of lanthanide ions in calixarene receptors. A strongly luminescent terbium(3+) complex, J. Chem, Soc. Chem, Commun. 878-879 (1990). 

Sabbatini, N. Guardigli, M. Mecati, A. Balzani, V. Ungaro, R. Ghidini, E. Casnati, A. Pochini, A. Encapsulation of lanthanide ions in calixarene receptors. A strongly luminescent terbium(3 +) complex. J. Chem. Soc., Chem. Commun. 1990, (12), 878-879. 

N. Sabbatini, M. Guardigli and I. Manet, Antenna effect in encapsulation complexes of lanthanide ions 69... 

The good encryption of lanthanide ions in DOTA-type molecules has also prompted the development of luminescent probes based on this structure, particularly by substituting DTMA, 1,4,7,10-tetrakis(methylcarbamoylmethyl)-1,4,7,10-tetraazacyclododecane. For instance, phenacyl and phenylphenacyl substituents have been grafted onto DTMA and the corresponding ligands, LI and L2 (Fig. 4.40) form stable 1 1 complexes in water with lanthanide ions (log/fi 12-13 at 295 K). The structure of [Tb(Ll)(H20)]3+ (Fig. 4.44) shows the ion well encapsulated into the cavity formed by the macrocyclic platform and... 

In the 1 1 complex of lanthanide nitrate with 12C4 or 15C5, the polyether does not encapsulate the lanthanide ion in its cavity due to the small cavity size, but is coordinated as tetra- or pentadentate ligand on one side as shown in Fig. 5.32. The three nitrates are bonded on the other side of lanthanide as bidentate. Thus the lanthanide is 10- and 11-coordinate in 12C4 and 15C5 complexes, respectively. In the 1 2 Sm(C104)3-15C5... 

N. Sabattini, M.Guardigliandl. Manet, 1996,23,69 (antenna effect in encapsulated complexes). G.E. Buono-core and H.LiB. Marciniak, Coord. Chem. Rev., 1990, 99,55 (quenching of excited states by lanthanide ions and chelates in solution). 

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