Evaluation of quinoline as a remote sensitiser for red and near-infrared emissive lanthanide(iii) ions in solution and the solid state

In order to evaluate quinoline as a remote sensitiser, we have prepared a DTPA based ligand, H₃L, bearing quinoline bisamide arms for the complexation of a range of lanthanide(iii) ions to give the neutral complexes LnL where Ln³⁺ = Y³⁺, Eu³⁺, Sm³⁺, Tb³⁺, Er³⁺, Yb³⁺, Nd³⁺, Gd ³⁺. Detection of the phosphorescence signal exhibited by the GdL complex at 77 K confirmed that the triplet energy level of the sensitiser at 21190 cm^-1 was suitable for the indirect population of a range of lanthanide luminescent states. A full photophysical analysis of the complexes reveals that SmL and EuL display red emission when excited through the ligand-based absorption band centred at 330 nm, extending the excitation to violet light around 370 nm. We demonstrate that quinoline sensitizes near-infrared emission in the YbL, ErL and NdL complexes, in powder form as well as in solution. Most importantly, the luminescence for YbL and NdL was sufficiently efficient to be detected in non-deuterated solvent.