Methodology for determining singlet oxygen quantum yield in dimethyl sulfoxide

Background Singlet oxygen ( 1 O 2 ) is a highly reactive oxygen species, playing an important role in a wide range of fields. The singlet oxygen quantum yield ( Ф Δ ) is a fundamental parameter for evaluating the efficiency of 1 O 2 generation by dye molecules. Various methods have been developed for Ф Δ measurement by exploiting the photoluminescence and chemical reactivity of 1 O 2 . We recently proposed a method for determining Ф Δ based on the reaction between Dimethyl Sulfoxide (DMSO) and 1 O 2 . However, due to the limited solubility of the reaction product, we supposed that the DMSO– 1 O 2 reaction would exhibit a termination point, which may affect the applicability of this method. Results In this work, we found that upon 1 O 2 generation, the absorption spectrum of DMSO initially changes and then reaches a plateau, which is attributed to the occurrence of a reaction termination in DMSO– 1 O 2 . Moreover, the occurrence time of the saturation point is inversely proportional to the excitation power density. When using the DMSO absorption change method to determine Ф Δ , the measurement must be conducted before this saturation point. Furthermore, due to the presence of the termination in DMSO– 1 O 2 reaction, the chemical probe method can still be applied for the determination of Ф Δ in DMSO under certain conditions. The relative degradation rate ( k ) of the probe exhibits an inflection point, with the slope k 2 after this point being greater than k 1 before it. This is because, prior to the inflection point, 1 O 2 generated by dye molecules react with both DMSO and chemical probe, and thus the degradation of probe reflects only a fraction of the total 1 O 2 . Hence, for the chemical probe method, measurements should be taken after inflection point. Significance This work provides a robust methodology for accurate determination of Ф Δ in DMSO, highlighting the necessity of selecting appropriate time windows tailored to each measurement method.