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

The sensitivity for singlet oxygen (O-1(2)) of two convenient O-1(2) 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-1(2,) it has very high, essentially diffusion-limited, reactivity towards O-1(2); it can trap up to 50% of all O-1(2) 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 O-1(2). 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 O-1(2), allowing for discrimination from other reactive oxygen species. The results presented here not only allow a comparative assessment of the usefulness of the two( 1)O(2) probes, but also provide a reference for an accurate absolute quantification of the amount of O-1(2) generated in an experiment from the observed absorbance bleach.