New water-soluble imidazolium-based and benzenetriol-based ligands and their 3:2 ligand-to-lanthanide sandwich-type complexes, Ln2(L1)3H2O, Ln2(L2)3H2O, and Ln2(L3)3H2O (Ln = Er(III), Gd(III), and Lu(III)), were isolated. Upon 980 nm excitation, the Er(III) complexes exhibited metal-centered up-conversion emission in the solid state and in aqueous solution. When incubated in HeLa cells, the complexes appear to localize in the mitochondria, and red and green Er(III)-centered up-conversion emission was observed.
Wallace et al. (Fri,) studied this question.