Imidodiphosphonate Ligands for Enhanced Sensitization and Shielding of Visible and Near-Infrared Lanthanides

Abstract

The design of coordination sites around lanthanide ions has a strong impact on the sensitization of their luminescent signal. An imidodiphosphonate anionic binding site is attractive as it can be functionalized with "remote" sensitizer units, such as phenoxy moieties, namely, HtpOp, accompanied by an increased distance of the lanthanide from the ligand high-energy stretching vibrations which quench the luminescence signal, hence providing flexible shielding of the lanthanide. We report the formation and isolation of Ln(tpOp)3 complexes where Ln = Er, Gd, Tb, Dy, Eu, and Yb and the Y(tpOp)3 diamagnetic analogue. The complexes are formed from reaction of KtpOp and the corresponding LnCl3•6H2O salt either by titration and in situ formation or by mixing and isolation. All complexes are seven-coordinated by three tpOp ligand plus one ethanol molecule, except for Yb(tpOp)3 which has no solvent coordinated. Phosphorus NMR shows characteristic shifts to support the coordination of the lanthanide complexes. The complexes display visible and near-infrared luminescence with long lifetimes even for the near-infrared complexes which range from 3.3 μs for Nd(tpOp)3 to 20 μs for Yb(tpOp)3. The ligand shows more efficient sensitization than the imidodiphosphinate analogues for all lanthanide complexes with a notable quantum yield of the Tb(tpOp)3 complex at 45%. We attribute this to the properties of the remote sensitizer unit and its positioning further away from the lanthanide, eliminating quenching of high energy C−H vibrations from the ligand shell. Calculations of the ligand shielding support the photophysical properties of the complexes. These results suggest that these binding sites are promising in the further development of the lanthanide complexes in optoelectronic devices for telecommunications and new light emitting materials.

Construction of Multifunctional Luminescent Lanthanide MOFs by Hydrogen Bond Functionalization for Picric Acid Detection and Fluorescent Dyes Encapsulation

“…Therefore, the relative intensity of 5 D 0 − 7 F 1 transition and 5 D 0 − 7 F 2 transition is usually used as the index of the coordination state and position symmetry of Eu 3+ . The calculated ratio of the intensity ratio of 5 D 0 − 7 F 2 and 5 D 0 − 7 F 1 is about 4.6, indicating that Eu 3+ in the structure occupy low-symmetry coordination sites with no inversion centers, 57,58 and this result is consistent with single-crystal Xray diffraction structural analysis. Because of the high sensitivity and the strongest emission, the emission peak at 616 nm based on 5 D 0 − 7 F 2 transition is usually used for the study of luminescent properties.…”

“…The solid-state excitation spectrum (Figure S7a) shows a maximum peak at 316 nm, which is similar to the absorption spectrum of L (Figure S8), indicating that energy can be efficiently transferred from the ligand to Eu 3+ . 57,58 The solid-state luminescent properties of Eu 2 L 3 were measured from 500 to 750 nm at room temperature. As shown in Figure S7b, under UV-light (365 nm) irradiation, the crystal powder exhibits intense red emissions.…”

Tuning the photophysical properties of lanthanide(iii)/zinc(ii) ‘encapsulated sandwich’ metallacrowns emitting in the near-infrared range

“…Another approach to minimize non-radiative deactivations is to create a protective hydrophobic environment around the Ln III ion as in the case of complexes formed with imidodiphosphonate ligands. 27,28 In addition, according to eqn (1), one more parameter that can be tuned and that lead to the enhancement of Q L Ln is the radiative lifetime. The validity of this approach has been demonstrated in several studies.…”

Manipulation of Molecular Vibrations on Condensing Er3+ State Densities for 1.5 μm Application

“…Organic erbium materials contain organic chromophores that strongly absorb visible light to sensitize Er 3+ excitations so as to reduce excitation power by orders of magnitude, − and approaches include polymers, , single molecules, − and molecular composites/hybrids. − This sensitization means that ideally a cheap and incoherent light source (LED or integrated OLED) illuminating from the top can be used to pump organic erbium waveguides on a compact scale. In contrast to inorganic erbium materials, where the photoexcitation is into the 4 I 13/2 or 4 I 11/2 states, organic sensitizers usually have exciton energies > ∼2 eV, which will sensitize to energy states of Er 3+ ions above the 4 I 11/2 level.…”