Luminescence and Relaxometric Properties of Heteropolymetallic Metallostar Complexes with Selectively Incorporated Lanthanide(III) Ions

The synthesis and characterization of two diethylenetriaminepentaacetic acid (DTPA) based heteropolymetallic metallostar lanthanide complexes with the general formulas (GdL1)(3)Ln and (GdL2)(3)Ln are described. The synthesis uses a synthetic approach recently developed in our group for the selective complexation of gadolinium(III) and luminescent lanthanide ions with a ditopic ligand to form highly paramagnetic and luminescent metallostar complexes. The luminescence data and relaxometric studies suggest the potential applicability of the complexes as bimodal contrast agents for magnetic resonance and optical imaging. Owing to the higher excited state of L-1, better sensitization was observed for all (GdL1)(3)Ln complexes than for (GdL2)(3)Ln. A large increase of the quantum yield from 1.5 to 9.8% was observed for the (GdL1)(3)Eu complex compared with (GdL2)(3)Eu, whereas the (GdL1)(3)Tb complex exhibited a quantum yield (QY) of 30.9% compared with 15.3% for (GdL2)(3)Tb. A slight increase of the QY from 0.8 to 1.2% was observed for the Dy(III) complex when switching from ligand L-2 to L-1. The nuclear magnetic relaxation dispersion (NMRD) measurements of the (GdL2)(3)Ln complexes (Ln = Eu-III, Dy-III, Tb-III) showed respective longitudinal relaxivity (r(1)) values of 24.27, 22.80 and 21.72 s(-1) mmol(-1) per metallostar complex at 310 K and 20 MHz.