Sensitization 3-diketonate ligands

The field of development of sensitizers for NIR-emitting lanthanide ions is currently booming. A large number of examples can be found in the literature, such as /3-diketone, ligands based on 8-hydroxyquinolinate, complexes with transition metal ions, MOFs, macrocyclic ligands, and so on. 

Lanthanide /3-diketonates are complexes of /3-diketone ligands (1,3-diketones) with lanthanide ions. These complexes are the most popular and the most intensively investigated luminescent lanthanide coordination compounds (see P-Diketonate). Three main types of lanthanide(III) /3-diketonate complexes have to be considered fra complexes, Lewis base adducts of the tris complexes (ternary lanthanide /3-diketonates), and tetrakis complexes. Most Eu +/3-diketonate complexes show an intense visible luminescence, but many /3-diketonates are not good ligands to sensitize the luminescence of Tb + ions. NIR luminescence can be... 

Strong light absorption by the jS-diketonate ligands is an advantage for sensitizing the luminescence of lanthanide ions by the antenna effect, but this property limits the usefulness of the rare-earth jS-diketonate complexes as laser materials. In order to achieve uniform excitation of the solutions containing the rare-earth chelate at the concentration required for laser... 

As it is well known, sensitization of Ln-centered luminescence can be achieved via an intramolecular energy transfer upon excitation of organic ligands, instead of using direct excitation of the weak Lnm absorption bands. This phenomenon now called antenna effect or luminescence sensitization has first been observed in 1942 by Weissman for europium(III) complexes formed with salicylaldehyde and with /3-diketonates, more particularly benzoyl-acetonate (ba, 48a), dibenzoylmethanate (dbm, 48b) and wieta-nitrobenzoylacctonatc (47a, fig. 41) (Weissman, 1942). 

In order to evaluate the efficacy of the chromophores used by various authors for the sensitization of the NIR emission of Lnm ions, the photophysical properties, lifetimes and quantum yields, of the complexes described in the previous sections are listed in table 21 for Ndm, table 22 for Er111, and table 23 for Ybm. Within a table, data are listed in order of increasing excitation wavelength. Only ligands substituted by a specific chromophore are listed in these tables. That is for instance, parent calix[n]resoicinarenes and calix[n]arenes are not included since relevant data are given in tables 7 and 8. The same remark is valid for simple tris(/3-diketonates) for which quantitative data are listed in figs. 42, 45, and 46, tables 10 and 11, as well as for triphenylmethane dyes (tables 14 and 15). 

Figure 2.50 Molecular structure of [Tb2(L )6(fi -0(CH2)2NHMe2)2] -CtHs. Fluorine atoms and solvate toluene molecule are omitted for clarity [81]. (Reprinted with permission from S.V. Eliseeva, O.V. Kotova et al, Role of the ancillary ligand V,V-dimethylaminoethanol in the sensitization of Eu and luminescence in dimeric P-diketonates, The Journal of Physical Chemistry A, 112, 3614-3626, 2008. 2008 American Chemical Society.)...

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