A chemical approach towards photosynthetic reaction center (2)

Abstract

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, kCS and kCR, were precisely determined by tracing a characteristic sharp absorption band around 715 nm due to (Im)−, kCS is essentially solvent polarity independent, while kCR 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. © 1994, Walter de Gruyter. All rights reserved.