Accessing Lanthanide-to-Lanthanide Energy Transfer in a Family of Site-Resolved [Ln(III)Ln(III)'] Heterodimetallic Complexes.

The ligand H 3 L (6-(3-oxo-3-(2-hydroxyphenyl)propionyl)-pyridine-2-carboxylic acid), which exhibits two different coordination pockets, has been exploited to engender and study energy transfer (ET) in two dinuclear [Ln(III)Ln(III)'] analogues of interest, [EuYb] and [NdYb]. Their structural and physical properties have been compared with the also newly synthesised analogues featuring no possible ET ([EuLu], [NdLu] and [GdYb], respectively) and with the corresponding homometallic [EuEu] and [NdNd] analogues, previously reported. Photophysical data suggest that ET between Eu(III) and Yb(III) does not occur to a significant extent, while emission from Yb(III) originates via sensitization from the ligand. In contrast, energy migration seems to be occurring between the two Nd(III) centers in [NdNd], as well as in [NdYb], where Yb(III) luminescence is thus in part sensitised by ET from Nd. This study shows the versatility of this molecular platform to further the investigation of lanthanide-to-lanthanide ET phenomena in defined molecular systems.