Type-I organic photosensitizers with two complementary reactive oxygen species based on donor-acceptor (D-A) molecules

Type-I photosensitizers (PSs) are considered to be a better choice for photodynamic therapy (PDT) because they can efficiently generate reactive oxygen species (ROS) in the hypoxia condition of tumor, showing less oxygen dependence. However, there are relatively few reported highly efficient type-I organic PSs, especially those simultaneously generated two or more species of type-I ROS. Herein, based on electron-acceptor of 9,10-phenanthrenequinone (PQ), a D-A-D structural type-I PS of PPQ constructed from electron-donor of 9-phenyl-carbazole (PCZ) was firstly developed and could simultaneously produce two type-I ROS under white light irradiation. As the generated ROS of hydroxyl radical (•OH) and superoxide anion radical (O2•−) possessed complementary oxidizing ability and radical lifetime, PPQ showed excellent PDT effects for tumor cells under normoxia or hypoxia. The ability of ROS generation and PDT performance of PPQ were better than those of another PQ derivative (TPQ) constructed with common electron-donor triphenylamine (TPA). More importantly, experiments in aqueous solution and vitro both revealed that •OH generated not only from the well-known transformation of O2•− but also direct electron transition from water to triplet excited PS, which demonstrated the oxygen dependence of type-I PSs more clearly. This new type-I PS offers an opportunity to obtain deep insights of the mechanism of type-I PSs, and provides a new strategy for development of type-I PSs.