Jean-Claude Bunzli - Visible and near-infrared luminescence of lanthanide-containing dimetallic triple-stranded helicates: Energy transfer mechanisms in the Sm-III and Yb-III molecular edifices

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      Silva,F.R.G.E., Malta,O.L., Reinhard,C., Gudel,H.U., Piguet,C.,   Moser,J.E., Bunzli,J.C.G. Journal of Physical Chemistry   A 2002 106 (9) 1670-1677

      Abstract: The photophysical properties of the   triple-stranded dimetallic helicates [Ln(2)(L-C-2H)(3)].H2O (Ln =   Nd, Sm, Dy, Yb) are determined in water and D2O Solutions, and   energy transfer processes are modeled for Sm-III. The   luminescence of Nd-III, SMIII, and Yb-III is sensitized by   (L-C-2H)(2-), but the energy transfer from the ligand to the   Ln(III) ions is not complete, resulting in residual ligand   emission. The luminescence of the Nd-III helicate is very weak   due to nonradiative de-excitation processes. On the other hand,   the WIT and Sm-III helicates exhibit fair quantum yields, 1.8%   and 1.1% in deuterated water, respectively. The energy transfer   rates between (L-C-2H)(2-) and Sm-III levels are calculated by   direct and exchange Coulomb interaction models. This theoretical   modeling coupled to numerical solutions of the rate equations   leads to an estimate of the emission quantum yields in H2O and   D2O, which compares favorably with experimental data. The main   component of the ligand-to-metal energy transfer (97.5%) goes   through a 3pipi* --> (5)G(5/2)((1)) path, and the operative   mechanism is of the exchange type, For the Yb-III helicate, minor   effects of oxygen on the sensitization of Yb-III and nanosecond   time-resolved spectroscopy point to the energy transfer mechanism   being consistent with a recently proposed pathway involving fast   electron transfer and Yb-II. No up-conversion process could be   identified. Ligand-field splitting of the F-2(5/2) (3E(1/2) +   E-3/2) and F-2(7/2) (2E(1/2) + E-3/2) levels of Yb-III is   consistent with D-3 symmetry

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