Photosensitized generation of singlet oxygen has attracted a great deal of interest reaching applications in various fields owing to its high biological activity and strong oxidation, including organic synthesis, wastewater treatment, and photodynamic therapy (PDT). Although singlet oxygen can be produced in a variety of ways, triplet state energy transfer from some organic molecules under light illuminations is one of the most efficient and controllable way to produce the active oxygen species, where the organics are called photosensitizers.