Figure 1. A schema showing oxidation of a sterically hindered amine TPC (2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide) by singlet oxygen to give rise to the nitroxide radical, and representative ESR spectra of the laser-irradiated mixtures containing rose bengal and a sterically hindered amine TPC.

The mixture containing 450 mM TPC and 0, 1 or 10 µM rose bengal was irradiated by the laser light with a wavelength of 532 nm for 60 s. Open circle and closed circle indicate Mn²⁺ marker and the nitroxide radical, respectively.