Sensitized near-infrared luminescence of NdIII, YbIII and ErIII complexes by energy transfer from a ruthenium antenna

Abstract A series of new ruthenium–lanthanide bimetallic complexes bridged by bibenzimidazole (BibzImH 2 ) group were synthesized. The luminescent ruthenium bibenzimidazole complex, [(bpy) 2 Ru(BibzImH 2 )] 2+ , with a vacant diimine site, was used as a ‘complex ligand’ to prepare three new heterodinuclear d–f complexes by attaching a {Ln(dik) 3 } fragment (Ln = Nd, Yb, or Er); (dik = tta(trifluoro theonyl acetone)) at the vacant site. All of the prepared complexes were characterized by a variety of spectral techniques. Upon excitation at the MLCT absorption band of Ru II , due to efficient energy transfer, sensitized emission occurs from lanthanide centre in the near-infrared region. The lanthanide centre has low-energy f–f excited states, which are capable of accepting energy from the 3 MLCT excited state of the Ru(II) centre, leading to the quenching of 3 MLCT luminescence of the Ru(II) centre and subsequent sensitized lanthanide(III)-based luminescence in the near-IR region. Because BibzImH 2 is a short bridging ligand, it is able to assist in faster energy transfer from Ru(II) to Ln (III). The Nd(III) species was found to be the most effective for quenching the 3 MLCT luminescence of the ruthenium component because of the high density of the f–f excited states of the appropriate energy, which make it as effective an energy-acceptor as Er(III) and Yb(III) complexes.