Efficient 0.4 μm-1.6 μm emission from muffin-shaped nine-coordinated ternary samarium(III) and erbium(III) complexes

Two nine coordinated lanthanide(III) complexes with the general formula [Ln(tfac)₃(tptz)] [Ln = Sm(III) (Sm1) or Er(III) (Er1); tfac is the anion of 1,1,1-trifluoro-2,4-pentanedione and tptz = 2,4,6-tri(2-pyridyl)-1,3,5-triazine] exhibiting emissions in the visible to near-infrared (NIR) region of the electromagnetic (EM) spectrum were synthesized. The molecular structure of the complexes was established using the single-crystal X-ray diffraction (SC-XRD) method, which explicitly confirms the formation of the nine-coordinated complexes with an LnO₆N₃ coordination sphere. Hirshfeld surface analysis reveals the presence of different non-covalent interactions (NCIs) and their role in stabilizing the molecular structure. The optical properties of Sm1 and Er1 were analysed and discussed in detail using UV-Vis-NIR absorption, steady-state emission and excited-state decay dynamics. Upon ligand-centred excitation, either in the solid state or in solution, Sm1 and Er1 exhibit their typical f-f emissions, covering a wide range of 400-1600 nm. Both complexes display a sizeable excited lifetime and fall in the category of efficient lanthanide materials. A possible emission mechanism involved in the sensitized visible and NIR emission is also proposed based on the available data set.