Long-Lived Near-Infrared Luminescent Lanthanide Complexes of Imidodiphosphinate “Shell” Ligands

Near-infrared emitting complexes of Nd(III), Er(III), and Yb(III) based
on hexacoordinate lanthanide ions with an aryl functionalized
imidodiphosphinate ligand, tpip, have been synthesized and fully
characterized. Three tpip ligands form a shell around the lanthanide
with the ligand coordinating via the two oxygens leading to neutral
complexes, Ln(tpip)3. In the X-ray crystal structures of Er(III) and
Nd(III) complexes there is evidence of CH−π interactions between
the phenyl groups. Photophysical investigations of solution samples
of the complexes demonstrate that all complexes exhibit relatively
long luminescence lifetimes in nondeuteurated solvents. Luminescence studies of powder samples have also been recorded for
examination of the properties of NIR complexes in the solid state
for potential material applications. The results underline the effective
shielding of the lanthanide by the twelve phenyl groups of the tpip
ligands and the reduction of high-energy vibrations in close
proximity to the lanthanide, both features important in the design
of NIR emitting lanthanide complexes.