A phototoxic thulium complex exhibiting intracellular ROS production upon 630 nm excitation in cancer cells.

A lanthanide(III) complex with a thulium metal centre connected via a terpyridine unit to a light harvesting antenna with strong absorption in the therapeutic window [>590 nm] was synthesised and tested as a possible photosensitiser (PS) in photodynamic therapy (PDT). The complex exhibited significant phototoxic activity on cancer cells upon irradiation in the therapeutic window and from intracellular and solution studies ROS production was identified as the compound's phototoxic mode of action. In cell viability assays, a 10-fold lowered IC 50 value was obtained upon irradiation compared to the dark control.