Synthesis and photoluminescence properties of pink luminescent heteroleptic Sm(III) complexes; the role of DMSO in transforming the inner coordination sphere and on photophysical properties. Sparkle/RM1 calculation

Abstract

Three new heteroleptic pink luminescent samarium complexes of the type [Sm(tfaa)3L] and [Sm(tfaa)3]2L′ were synthesized [where tfaa=1,1,1-trifluoro-2,4-pentanedione and L=2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) and L′=2,2′-bipyridimidine (bpm)] and characterized by elemental analysis, FT-IR, thermogravimetry and 1H NMR spectroscopy. The coordination geometries of the Sm(III) complexes were calculated by the Sparkle/RM1 model. The complexes have excellent thermal properties and melt at 197 [Sm(tfaa)3bpy], 198 [Sm(tfaa)3phen] and 186°C [Sm(tfaa)3]2bpm. The photophysical properties of the complexes were analyzed in chloroform (non-coordinating) and DMSO (coordinating). Pink luminescence is observed for all the complexes. Substitution of the water molecule from the coordination sphere of [Sm(tfaa)3H2O] by ancillary ligands leads to a 4.71 (phen and bpy) and 3.26 (bpm) fold increase in the luminescence lifetime. This enhancement originates mainly due to (i) better sensitization of the Sm(III) ion by the ancillary ligands and (ii) elimination of non-radiative deactivation pathways through the harmonics of the O–H vibration. The most interesting feature of the study is the similar spectral band shapes, intensities, lifetimes and quantum yields for the complexes in DMSO. The similar spectral shapes and lifetimes of the complexes in DMSO are due to the replacement of the ancillary ligands (i.e. bpy, phen and bpm) and water, and the transformation of the complexes into [Sm(tfaa)3(DMSO)2] species in solution.