Oxygen concentration dependent studies reveal the Stern-Volmer constant K_SV of ZnPc

The determination of the Stern-Volmer constant (K_SV) for photosensitizers, a key parameter for characterizing energy transfer efficiency to oxygen, enables the understanding and optimization of photosensitizer functionality. In this study, a strategy was proposed for determining the K_SV by replacing the analysis of the oxygen-dependent behavior of fluorescence intensity with a direct correlation between singlet oxygen quantum yield (Φ_Δ) and molecular oxygen. Zinc phthalocyanine (ZnPc) was selected for this work due to its promising photosensitizing properties. Through theoretical analysis using the rate equation model and experimental absorption measurements, the K_SV of ZnPc was found to be 2.4(2) μM⁻¹. To verify the accuracy of the K_SV, an oxygen-varying correlated fluorescence methodology was applied, reinforcing the reliability of the results. In addition, the determination of the K_SV is achievable even in the absence of specific Φ_Δ values and without the use of a standard reference.