Stable, cytotoxic, and fluorescent Ti(IV) phenolato complexes – synthesis, characterization, and potential use in live cell imaging

Two fluorescent titanium(IV) complexes were synthesized in high yields and purities, each with a tetradentate diaminobis(phenolato) “salan”-type ligand and the chelating and fluorescent alizarin ligand. The complexes exhibited an improved hydrolytic stability relatively to previously reported fluorescent Ti(IV) salen complexes (t_1/2 for hydrolysis in 10% D₂O up to ∼ 150 h), and high in vitro cytotoxicity toward two ovarian and cervix human cancer cell lines (IC₅₀: 1–15 µM). Their excitation at 530 nm resulted in red fluorescence, with emission peaks at 610 and 626 nm. The complexes were tracked under confocal microscopy in live HeLa cells for 48 h, resulting in significant cellular accumulation of both, which exemplifies their possible use for live cell imaging.