The detection sensitivity of commonly used singlet oxygen probes in aqueous environments

The sensitivity for singlet oxygen (¹O₂) of two convenient ¹O₂ probes, 1,3-diphenylisobenzofuran (DPBF) and 9,10-Anthracenediyl-bis(methylene)dimalonic acid (ABDA), has been investigated in different aqueous environments. Both probes are commercially available at reasonable cost and can be used with standard UV-vis spectrometers. Although DPBF is not soluble in neat water and is not specific to the detection of ¹O₂, it has very high, essentially diffusion-limited, reactivity towards ¹O₂; it can trap up to 50% of all ¹O₂ created in alcohol/water or micellar solution, and even more when replacing H₂O by D₂O, which makes it highly useful when the process under investigation does not yield much ¹O₂. On the other hand, ABDA has a much lower reactivity, reacting with only 2% of the singlet oxygen generated in H₂O, as well as a smaller extinction coefficient, resulting in a much smaller spectroscopic response, but is soluble in neat water and is specific for ¹O₂, allowing for discrimination from other reactive oxygen species. The results presented here not only allow a comparative assessment of the usefulness of the two ¹O₂ probes, but also provide a reference for an accurate absolute quantification of the amount of ¹O₂ generated in an experiment from the observed absorbance bleach.