Synthesis, Photophysical Properties, and Living Cell Imaging of Theranostic Half-Sandwich Iridium–4,4-Difluoro-4-bora‑3a,4a‑diaza‑s‑indacene (BODIPY) Dyads

We report the synthesis, characterization, and photophysical properties of two new cyclometalated half-sandwich iridium­(III) complexes having the general formula [(η5-Cp*)­Ir­(ppy)­Z]­PF6 where η5-Cp* = pentamethylcyclopentadienyl and ppy = 2-phenyl-pyridine as C∧N-chelating ligand and Z = 3- or 4-pyridyl-BODIPY (BODIPY = 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene dye containing a 3- or 4-pyridyl group at the meso position). The molecular structure of both complexes has been determined by X-ray crystallography. The photophysical properties of the dyads were investigated and compared to the pyridyl-BODIPY precursors. Antiproliferative studies demonstrated that one of the compounds was highly active with submicromolar IC50 on a panel of cancer cell lines. The replacement of the chlorido ligand by the pyridyl-BODIPY increased the lipophilicity of the complexes and slowed down the hydrolysis rate, which in turn increased the cytotoxicity of the metallodrug candidate. For the first time, cell uptake of one of the dyads was monitored by living cell fluorescence imaging. Interestingly, extremely fast internalization was observed the rate of which was temperature-dependent.