Responsive, di-metallic lanthanide complexes of a piperazine-bridged bis-macrocyclic ligand: modulation of visible luminescence and proton relaxivity?

Dalton Transactions Pub Date: 2010-02-25 DOI: 10.1039/B923988J

Abstract

The synthesis of a new functionalised bis-macrocyclic ligand (L1) is described together with the corresponding LnIII complexes, Ln2-L1 (Ln = GdIII, EuIII). Phosphorescence measurements on Gd2-L1 at 77 K allowed the ligand-centred triplet state (3π–π*) to be estimated at ca. 28500 cm?1. Steady state and time-resolved measurements confirmed emission from the f-centred excited state (5D0) for Eu2-L1. 1H NMRD profiles revealed the longitudinal proton relaxivity (r1) of Gd2-L1 to be 8.3 mM?1s?1(30 MHz, 25 °C). The interaction of CuII and HgII with the lanthanide complexes was probed using luminescence and relaxivity measurements. Addition of CuII (10 eq.) resulted in quenching of the EuIII emission, but no increase in r1 of the GdIII dimer. Addition of HgII (10 eq.) caused changes to the hypersensitive emission bands of EuIII together with an increase in r1 of Gd2-L1 to be 10.3 mM?1s?1(30 MHz, 25 °C) suggesting a net increase in hydration at the GdIII centres.

Graphical abstract: Responsive, di-metallic lanthanide complexes of a piperazine-bridged bis-macrocyclic ligand: modulation of visible luminescence and proton relaxivity
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