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

The sensitivity for singlet oxygen (O) of two convenient O 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 O, it has very high, essentially diffusion-limited, reactivity towards O; it can trap up to 50% of all O created in alcohol/water or micellar solution, and even more when replacing HO by DO, which makes it highly useful when the process under investigation does not yield much O. On the other hand, ABDA has a much lower reactivity, reacting with only 2% of the singlet oxygen generated in HO, as well as a smaller extinction coefficient, resulting in a much smaller spectroscopic response, but is soluble in neat water and is specific for O, allowing for discrimination from other reactive oxygen species. The results presented here not only allow a comparative assessment of the usefulness of the two O probes, but also provide a reference for an accurate absolute quantification of the amount of O generated in an experiment from the observed absorbance bleach.