1：Experimental Design and Method Selection:

The study involved synthesizing a phosphorus(V) complex of a pH-activatable porphyrin derivative (P(V)Por-NEt2) to enhance water solubility and ON/OFF switching performance. Theoretical models included DFT and TD-DFT calculations for molecular orbital analysis.

2：Sample Selection and Data Sources:

Samples included synthesized P(V)Por-NEt2 and reference compounds like Por-NEt2. Data were obtained from UV-Vis absorption, fluorescence, and phosphorescence measurements in various solvents and pH conditions.

3：Data were obtained from UV-Vis absorption, fluorescence, and phosphorescence measurements in various solvents and pH conditions. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included NMR spectrometers (JEOL ECS400, ECS600), mass spectrometer (Bruker compactTM), FT-IR spectrometer (JASCO FT/IR-4000), UV-Vis spectrophotometer (Hitachi U3310), fluorescence spectrometer (Horiba FluoroMax 4p), absolute photoluminescence quantum yield spectrometer (Hamamatsu C9920-02), fluorescence lifetime system (HORIBA TemPro), Nd3+:YAG laser (Tokyo Instruments Lotis II), photomultiplier tube (Hamamatsu R5509-42), monochromator (Ritsu MC-10N), amplifier (Stanford Research Systems SR445), photon counter (Stanford Research Systems SR400), pH meter (DKK-TOA HM-25G). Materials included solvents like DMSO, DMF, MeCN, MeOH, EtOH, 1-octanol, hydrochloric acid, sodium hydroxide, ultrapure water (Merck Millipore Direct-Q 3UV), and synthesized compounds.

4：Experimental Procedures and Operational Workflow:

Synthesis involved reacting Por-NEt2 with POCl3 in pyridine followed by methanol. Measurements included recording UV-Vis absorption spectra at various concentrations and pH values, fluorescence spectra and quantum yields, fluorescence lifetimes using time-correlated single-photon counting, phosphorescence of singlet oxygen using laser excitation and detection, and pH adjustment with HCl or NaOH. Quantum yields were determined relative to standards.

5：Data Analysis Methods:

Data were analyzed using exponential functions for fluorescence decay, equation S1 for pH dependence of quantum yields, and DFT/TD-DFT calculations for molecular orbitals and absorption spectra. Statistical errors were noted as ±10% for quantum yields.