New cyclometalated transition-metal based photosensitizers for singlet oxygen generation and photodynamic therapy

The aim of this review article is to introduce recent studies on an emergent class of singlet oxygen photosensitizers of potential applications to the photodynamic therapy, with a primary focus on the cyclometalated transition-metal complexes. Singlet oxygen photosensitization performances of various cyclometalated Ir and Pt scaffolds are reviewed, and the general photo-physical properties of relevant systems and the mechanisms of singlet oxygen production via photo-sensitization are also briefly discussed. Thus far, investigations of singlet oxygen sensitization by such Ir and Pt complexes are mainly carried out in organic solvents and under non-physiological conditions, while some research efforts have been made at examining the feasibility of applying pertinent cyclometalated complexes to photodynamic therapy.