pH-Dependent molecular switch based on Pv porphyrin

Water-soluble phosphorus(v) porphyrin with p-amino- phenoxy groups as axial ligands was obtained, and its photophysical and photochemical properties were investigated and rationalized using quantum chemical calculations. It was demonstrated that at pH ≥ 6.1 this porphyrin did not emit or generate singlet oxygen, whereas at pH ≤ 2.0 it completely converted into the N-protonated form, which exhibited fluorescence and the ability to generate singlet oxygen.