Synthesis, luminescence and quantum yields of Eu(III) mixed complexes with 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 1,10-phenanthroline-N-oxide

The new complex tris(4,4,4-trifluoro-1-phenyl-1,3-butanedionate)(1,10-phenanthroline-N-oxide)europium(III) has been synthesized, characterized, and its photophysical properties (excitation and luminescence spectra, and quantum yields) investigated down to 4.2 K. A similar complex containing H2O instead of phenNO molecules was also investigated for comparison. The more pronounced temperature dependence of the quantum yield q and the larger difference between the q values upon ligand and direct Eu3+ excitation for the hydrated compound show that there are other quenching processes operative, besides the expected multiphonon relaxation via the H2O vibrations. The results clearly show that the substitution of the water molecules by phenNO leads to greatly enhanced quantum yields (i.e. 30% vs. 66%, upon ligand excitation at 300 K) and longer D-5(0) lifetimes (380 mu s vs. 670 mu s respectively). This can be ascribed to a more efficient ligand-to-metal energy transfer and to less efficient non-radiative D-5(0) relaxation processes.