Photobleaching of Erythrosine B in Aqueous Environment Investigation Beyond pH

In the scientific literature, the term aqueous environment is loosely employed as it encompasses a broad range of different buffering agents. While there is an increasing number of experimental evidence that point toward specific buffer effects extending far beyond pH, the impact of the chemical nature of the buffering ions is often disregarded, especially in photochemical studies. Herein, we highlighted the importance of buffer specific effects on both the photobleaching and the singlet oxygen quantum yields of a dye in aqueous environments. For this study, we chose erythrosine B (EB) as our model photosensitizer as its photochemistry and photobleaching are well documented in the literature. We followed EB's photobleaching via absorption spectroscopy in four different aqueous solvents, including pure water, phosphate, Tris and HEPES buffer. These buffer systems were selected because they are commonly used in biochemical and biological applications. Our results show that specific buffer effects cannot be neglected. Indeed, the singlet oxygen quantum yield for EB is significantly different in HEPES compared to the other solvents. Furthermore, we showed that EB's photoproduct is highly dependent on the nature of the chemical buffer being used.