Abstract— EPR studies of the porphyrin‐sensitized photooxidation of 2, 2, 6,6‐tetramethyl‐piperidine to the nitroxide demonstrate that all the porphyrins examined are able to generate 1O2, although the efficiency of the photoprocess is dependent on the nature of the side chains. Incorporation of metal ions into the porphyrin molecule depresses or even inhibits the formation of 1O2. Comparison of these results with previously obtained kinetic data points out that the efficiency of porphyrins as photosensitizes is controlled by the lifetime of their lowest triplet state.
