Degradation of the samples was determined to be less than 3% over the course of the experiments based on their steady-state absorption spectra. The quantum yields were determined in back-to-back luminescence experiments of 6MP, Aza and phenalenone solutions under the same conditions, using the reported yield of 1 O2 generated by phenalenone as a standard (Δ = 0.98). 3. RESULTS