ESR1 and breast carcinoma: This selection is based on thefact that estrogen receptors are overexpressed in several types ofcancers, such as breast cancer. We employedclick chemistry to functionalize the ligands, as it is a facile andefficient approach to bioconjugation (Scheme a). We synthesizeda series of six new luminescent Ru­(II) complexes with the generalformula [Ru­(L-2)2(L-1)]2+, where L-2 is an ancillary polypyridine ligand and L-1 is a polypyridine estrogen-conjugated ligand (complexes 2–7, Scheme b).