Reactive Oxygen Species Mediated Activation of a Dormant Singlet Oxygen Photosensitizer: From Autocatalytic Singlet Oxygen Amplification to Chemicontrolled Photodynamic Therapy

Here we show the design, preparation, and characterization of a dormant singlet oxygen (1O2) photosensitizer that is activated upon its reaction with reactive oxygen species (ROS), including 1O2 itself, in what constitutes an autocatalytic process. The compound is based on a two segment photosensitizer–trap molecule where the photosensitizer segment consists of a Br-substituted boron-dipyrromethene (BODIPY) dye. The trap segment consists of the chromanol ring of α-tocopherol, the most potent naturally occurring lipid soluble antioxidant. Time-resolved absorption, fluorescence, and 1O2 phosphorescence studies together with fluorescence and 1O2 phosphorescence emission quantum yields collected on Br2B–PMHC and related bromo and iodo-substituted BODIPY dyes show that the trap segment provides a total of three layers of intramolecular suppression of 1O2 production. Oxidation of the trap segment with ROS restores the sensitizing properties of the photosensitizer segment resulting in ∼40-fold enhancement in 1O2...