Solvatochromic dual luminescence of Eu-Au dyads decorated with chromophore phosphines

Phosphine ligands, containing chromophore substituents -pi-spacer-NPh2 (pi-spacer = biphenyl, L1; naphthalene-ethynylphenyl, L2; and ethynyl-(phenylethynyl)anthracene, L3), were used to generate the corresponding gold(i) alkynyl complexes Au1-Au3 (alkynyl = ethynylphenyl-2,2 '-bipyridine, epbpy). These compounds demonstrate intense fluorescence, which originates from the bipolar donor-pi-acceptor systems of coordinated phosphines with negligible contribution from the epbpy fragment. Due to the charge transfer characteristic of the excited state, Au1-Au3 reveal significant emission solvatochromism (particularly discernible for Au2, 428 nm in cyclohexane -> 580 nm in acetonitrile). The bipyridine moiety of Au1-Au3 was utilized for binding these metalloligands to the {Eu(tta)(3)} red emitter (tta = 3-thenoyltrifluoroacetonate) to give a family of novel dyads Au1Eu-Au3Eu. Incomplete energy transfer from L1-L3 to lanthanide ions, which are primarily sensitized by diketonate ligands, leads to dual luminescence. Analogous to the parent complexes Au1-Au3, the fluorescence component of the dyads is highly sensitive to the solvent polarity that provides great opportunities for color tuning, including white light generation.