A CHEMICAL APPROACH TOWARDS PHOTOSYNTHETIC REACTION-CENTER .2.

Pyromellitimide(Im)-linked porphyrin arrays were prepared and their intramolecular electron-transfer reactions were studied by picosecond time-resolved transient absorption spectroscopy. In pyromellitimide-linked zinc porphyrin (M-Im), the rates of the photoinduced charge separation (CS) and charge recombination (CR) of the product ion pair (IP) states, k(CS) and k(CR), were precisely determined by tracing a characteristic sharp absorption band around 715 nm due to (Im)-. k(CS) is essentially solvent polarity independent, while k(CR) increases with solvent polarity. In 1,2-phenylene-bridged zinc diporphyrin-zinc porphyrin-pyromellitimide (D-M-Im) triads, 1(m)* is competitively quenched by D through energy transfer to give 1(D)*-M-Im and by Im through CS to give D-(M)+-(Im)-. Secondary IP states (D)+-M-(Im)- are formed via hole transfer from (M)+ to D. Sequential electron-transfer reactions that are the same type of the reaction mode of the reaction center are realized in zinc porphyrin-pyromellitimide-quinone (M-Im-Q) triads; 1(M)*-Im-Q) (M)+-Im)-->Q --> (M)+-Im-(Q)-. Finally, a more long-lived IP state is generated from D-M-Im-Q tetrads.