Influence of pulse-height discrimination threshold for photon counting on the accuracy of singlet oxygen luminescence measurement

Direct measurement of near-infrared (NIR) luminescence around 1270nm is the golden standard of singlet oxygen (¹O₂) identification. In this study, the influence of pulse-height discrimination threshold on measurement accuracy of the ¹O₂ luminescence that is generated from the photoirradiation of meso-tetra (N-methyl-4-pyridyl) morphine tetra-tosylate (TMPyP) in aqueous solution was investigated by using our custom-developed detection system. Our results indicate that the discrimination threshold has a significant influence on the absolute ¹O₂ luminescence counts, and the optimal threshold for our detection system is found to be about - 41.2mV for signal discrimination. After optimization, the derived triplet-state and ¹O₂ lifetimes of TMPyP in aqueous solution are found to be 1.73 ± 0.03 and 3.70 ± 0.04νs, respectively, and the accuracy of measurement was further independently demonstrated using the laser flash photolysis technique.