Synthesis and photophysical properties of kinetically stable complexes containing a lanthanide ion and a transition metal antenna group

Abstract

A series of bimetallic complexes has been prepared in which an octadentate DOTA-monoamide pocket containing a bound lanthanide ion is linked covalently to a Re^I or Ru^II bipyridyl unit via an alkyl spacer group. The transition metal chromophores incorporated in this way act as effective sensitisers for lanthanide-centred luminescence. The rate and efficiency of energy transfer are dependent upon the nature of the spacer group, and upon the nature of the lanthanide acceptor. For the RuNd diad, there is a long rise-time associated with the energy-transfer step, such that energy transfer is rate determining in H₂O, but not in D₂O. The results also lead us to suggest that energy transfer may precede formation of the ³M_(Ru/Re)L_(bpy)CT state and may be a competitive deactivation pathway for the precursor state (¹M_(Ru/Re)L_(bpy)CT).