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

Phosphine ligands, containing chromophore substituents –π-spacer–NPh2 (π-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–π-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.