Europium adducts, fluorescence

The fluorescence spectra of the europium adducts also provide information about the geometry of the complex. The lower the local site symmetry about the europium ion, the more numerous the lines in the spectrum. This fine structure results from internal Stark splitting of the ionic levels. The maximum number of lines into which each transition will be split as a function of geometry has been tabulated by several authors (II, 15, 32). The observation of a Do- Do transition for all the complexes reported indicates that none possesses a center of symmetry. 

Bhaumik (148) measured the rise time of the red fluorescence in some europium chelates. His data were collected with a stroboscopic instrument having a time-resolution capability of around 0.2 /xsec. Figure 40 shows the fluorescence-rise curve of the sDq- >1F2 transition in the piperidine adduct of the four-ligand europium dibenzoylmethide chelate. Data were collected at 77°K. 

Figure 40. Fluorescence rise and decay in the piperidine adduct of a four-ligand europium dibenzoylmethide chelate [from Ref. (148)].

The fluorescence properties of several europium and samarium ) -diketonates have been measured and assignments of the transitions made. Rare-earth element hexafluoroacetylacetonates with amino-acids have also been reported to fluoresce. The luminescence of the heptafluoroheptane-2,4-dione complexes of Sm, Eu, and Tb has been measured in dilute ethanol at pH8 and 610nm mixed-ligand complexes with 1,10-phenanthroline exhibited an enhanced luminescence. Photolysis of the Tb chelate of 2,2,6,6-tetramethylheptane-3,5-dione has been examined at 311 nm in various alcohols, and loss of one -diketone ligand found to be the primary photochemical step. A linear correlation was demonstrated between the quantum yield of dissociation of the complex and the formation constant of the complex-alcohol adduct. 

Europium, and to a lesser extent terbium, complexes of /3-diketones have been studied in solution and in the solid state by means of their fluorescence (luminescence) spectra. As explained further in Section 39.2.10, it is possible to relate the splitting of the Do—> F transitions of Eu " to the symmetry of the emitting complex, and studies of circularly polarized luminescence (CPL) spectra can give related information. Thus a study of EuCls and complexes of Eu with hexafluoroacetylacetone and four other /8-diketones in methanol or DMF showed that while EUCI3 itself had axial symmetry in solution, the complexes had orthorhombic symmetry. The emission spectra of solutions of adducts of Eu(dpm)3 with PhsPO or borneol have been studied at low temperatures where conformal lability is reduced the Ph3PO adduct has uniaxial symmetry but the bulky, less symmetrical bomeol molecule confers lower symmetry on its adducts. ... 

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