Visible and Near-Infrared Luminescence of Lanthanide-Containing Dimetallic Triple-Stranded Helicates:  Energy Transfer Mechanisms in the Sm^III and Yb^III Molecular Edifices

Abstract

The photophysical properties of the triple-stranded dimetallic helicates [Ln 2 (L C -2H) 3 ]‚H 2 O (Ln ) Nd, Sm, Dy, Yb) are determined in water and D 2 O solutions, and energy transfer processes are modeled for Sm III . The luminescence of Nd III , Sm III , 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 Yb III 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 H 2 O and D 2 O, which compares favorably with experimental data. The main component of the ligandto-metal energy transfer (97.5%) goes through a 3 ππ* f 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 2 F 5/2 (3E 1/2 + E 3/2 ) and 2 F 7/2 (2E 1/2 + E 3/2 ) levels of Yb III is consistent with D 3 symmetry.

Tuning the Decay Time of Lanthanide‐Based Near Infrared Luminescence from Micro‐ to Milliseconds through d→f Energy Transfer in Discrete Heterobimetallic Complexes

“…It can be interpreted as arising from metal ions in a trigonal site with D 3 symmetry, for which the irreducible representations of the total angular momentum operator lead to four sublevels for Yb-( 2 F 7/2 ) and three sublevels for Yb( 2 F 5/2 ) (Figure 9a). [28] We thus expect four transitions from the lowest crystal-field sublevel of Yb( 2 F 5/2 ) to the Yb-( 2 F 7/2 ) manifold (Figure 8b, and Figure S5 and Table S13 in the Supporting Information). At 10 K, the total splitting of Yb-( 2 F 7/2 ) amounts to 304 cm À1 in CrYb and 303 cm À1 in RuYb, which confirms the similarity of the lanthanide coordination spheres in these helicates.…”

A new tetrakis β-diketone ligand for NIR emitting LnIII ions: luminescent doped PMMA films and flexible resins for advanced photonic applications

“…Furthermore, a weak anti-Stoke band around 950 nm is also present in the room temperature emission spectrum of 4 but is absent from the 77 K spectrum, which conrms its "hot band" nature. 33 The spectra recorded at low temperature (Fig. 8) emission when excited at 500 nm, both at 298 K and 77 K. The efficiency of visible and NIR emission of complexes 1, 3, and 4 can be examined in terms of overall quantum yields (F ov ) Table 2 and typical decay proles obtained for the solid-state samples are shown in Fig.…”

The First Example of Near-Infrared 4f Luminescence of Sandwich-Type Lanthanide Phthalocyaninates

“…It can be proposed that, the observed 4f luminescence of Yb III in phthalocyaninates may be due to one of the following factors. The Förster-type of energy transfer is forbidden by the selection rule |ΔJ| = 2, 4, 6 for 2S+1 L j -levels for the resonance 2 F 5/2 -level of Yb III ion, [39,40] moreover, the spectral overlapping of the energy levels of the donor and acceptor is minimal. Therefore, this mechanism of energy transfer (from both singlet and triplet levels of phthalocyanine) is impossible, unlike Dexter migration, because |ΔJ| = 1.…”