Abstract: Upon the addition of imidazole (Im) to the artificial photosynthetic systems composed byZnTPP/BQand p-H₂TPP-NH-CO-CH₂-BQ, half-lives of ESR signals of semibenzoquinone radical BQ^·- and -CH₂-BQ^·- are significantly prolonged by the secondary electron transfer pathway from imidazole toporphyrin cation in polar solvents.The imidazole cation radicals(Im^·+) can simultaneously be identified byPBN(spin trap) both in BQ/ZnTPP/Im and p-H₂TPP-NH-CO-CH₂-BQ systems when laser-flashing.Onthe basis of our ESRobservation, a secondary electron transfer mechanism can be proposed as follows;(1) TPP+hv→TPP^*; (2) TPP^*+BQ→TPP^·++BQ^·-;(3) TPP^·+ +Im →TPP+Im^·+.

Key words: Imidazole radical, Secondary electron transfer, Artificial simulation on PS Ⅱ reaction center, ESR, Spin trapping