Photomedicine with Inorganic Complexes: A Bright Future

Photo-induced reactions have the potential to revolutionize the fields of photomedicine and intelligent drug delivery by providing means of specifically inducing a chemical transformation in biological environments. The molecule that absorbs light and engages in photo-induced reactions is called the photosensitizer, and is the key component in this process. It transforms photon energy into a variety of reactions, such as photosensitized oxidations in photodynamic therapy (PDT) and ligand exchange in photoactivated chemotherapy (PACT). Ruthenium complexes, in particular, offer the possibility to maximize and fine-tune each of these reactions by changing the electronic properties, hydrophobicity, and steric hindrance of the ligands, thus affecting the energy and reactivity of the excited states. The field has advanced immensely in the last decade and we aim here to report on major achievements of ruthenium compounds for phototherapy. We will also discuss the mechanism of light-induced toxicity, the potential of upconverting systems for the activation of this type of drugs, as well as initial steps towards commercial applications of ruthenium complexes as PDT agents.