Improvement of the ON/OFF Switching Performance of a pH-Activatable Porphyrin Derivative by the Introduction of Phosphorus(V)

摘要： An activatable photosensitizer for singlet oxygen is of significance due to its potential applications for high tumor-specific photodynamic therapy and diagnosis. In this study, a pH-activatable system that enables the specific photosensitization of singlet oxygen at a low pH was developed based on the complexation of a porphyrin–aniline conjugate with phosphorus(V). As a result of complexation with phosphorus, the water solubility of the porphyrin–aniline conjugate was improved by 100 times. Furthermore, this complexation strongly suppressed the singlet-oxygen-generating activity of the porphyrin photosensitizer under basic conditions, and the quantum yield of the singlet oxygen photosensitization markedly increased under acidic conditions. Based on these improvements, an extremely high ON/OFF switching ratio of the quantum yield was obtained (>400 times).