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)3Ln and (GdL2)3Ln 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 L1, better sensitization was observed for all (GdL1)3Ln complexes than for (GdL2)3Ln. A large increase of the quantum yield from 1.5 to 9.8 % was observed for the (GdL1)3Eu complex compared with (GdL2)3Eu, whereas the (GdL1)3Tb complex exhibited a quantum yield (QY) of 30.9 % compared with 15.3 % for (GdL2)3Tb. A slight increase of the QY from 0.8 to 1.2 % was observed for the Dy(III) complex when switching from ligand L2 to L1. The nuclear magnetic relaxation dispersion (NMRD) measurements of the (GdL2)3Ln complexes (Ln = EuIII, DyIII, TbIII) showed respective longitudinal relaxivity (r1) values of 24.27, 22.80 and 21.72 s–1 mmol–1 per metallostar complex at 310 K and 20 MHz.status: publishe