The ESR signals with hyperfine structure were detected in the photolysis of Hypocrellin A or B and in the electron transfer interaction between the ground state of Hypocrelline and aliphatic amines in solns. The same signals could also be detected in the solns. of electrochem. reduction of Hypocrellins. It confirmed that signals arose from the semiquinone radical anion of Hypocrellins. No ESR signal could be detected in solution for interaction between and ground state of Hypocrellins with aromatic amines. The hydroxyl group adjacent to the quinonoid carbonyl in perylene quinone nucleus may stabilize the semiquinone radical anion. In case the proton in hydroxyl group dissociated completely no ESR signal could be observed either in the ground state or in the excited state in our experiments In addition, the absorption spectra of semiquinone radical and the interactions between Hypocrellins with aliphatic amines have been studied in this paper.

Key words: ELECTRON SPIN RESONANCE SPECTROMETRY, REDUCTION, ELECTROCHEMISTRY, SEMIQUINONE, PHOTOINDUCED, HYPOCRELLIN, FREE RADICALS