Visible and near-infrared emission from lanthanoid β-triketonate assemblies incorporating cesium cations

This work is supported by the Australian Research Council and a Royal Society International Exchanges Grant. EZ-C thanks EPSRC (EP/M02105X/1) for support. LAG and BLR thank Curtin University for the postgraduate scholarship. The authors acknowledge access to the facilities at the Centre for Microscopy, Characterisation and Analysis, University of Western Australia The reaction of the β-triketonate ligands tris(4-methylbenzoyl)methanide and tribenzoylmethanide with the trivalent lanthanoid Eu3+, Er3+, and Yb3+ in the presence of Cs+ afforded polymeric structures where the repeating units are represented by bimetallic tetranuclear assemblies of formulation {[Ln(Cs)(β-triketonate)4]2}n. The only exception is the structure formed by reaction of tris(4-methylbenzoyl)methanide, Yb3+, and Cs+, which yielded a polymeric assembly where the repeating units are mononuclear Yb3+ complexes bridged by Cs+ cations. Photophysical measurements on the obtained materials confirmed efficient sensitization from the ligand excited states to the 4ƒ* excited stated of the three lanthanoids. According to transient absorption data, Er3+ and Yb3+ are sensitized via energy transfer from the triplet state of the β-triketonate ligands. On the other hand, energy transfer to Eu3+ seems to occur via an alternative pathway, possibly directly via the singlet state or through ligand-to-metal charge transfer states. The emission measurements confirm efficient sensitization for all three lanthanoids and bright near-infrared emission for Er3+ and Yb3+, a characteristic that seems to be linked to the specific chemical structure of the β-triketonate ligands. Publisher PDF