Photocytotoxicity of Thiophene- and Bithiophene-Dipicolinato Luminescent Lanthanide Complexes

New thiophene-dipicolinato-based compounds, K2nTdpa (n = 1, 2), were isolated. Their anions are sensitizers of lanthanide ion (LnIII) luminescence and singlet oxygen generation (1O2). Emission in the visible and near-infrared regions was observed for the LnIII complexes with efficiencies (ϕLn) ϕEu = 33% and ϕYb = 0.31% for 1Tdpa2– and ϕYb = 0.07% for 2Tdpa2–. The latter does not sensitize EuIII emission. Fluorescence imaging of HeLa live cells incubated with K3[Eu­(1Tdpa)3] indicates that the complex permeates the cell membrane and localizes in the mitochondria. All complexes generate 1O2 in solution with efficiencies (ϕO12) as high as 13 and 23% for the GdIII complexes of 1Tdpa2– and 2Tdpa2–, respectively. [Ln­(nTdpa)3]3– (n = 1, 2) are phototoxic to HeLa cells when irradiated with UV light with IC50 values as low as 4.2 μM for [Gd­(2Tdpa)3]3– and 91.8 μM for [Eu­(1Tdpa)3]3–. Flow cytometric analyses indicate both apoptotic and necrotic cell death pathways.