A chemical approach towards the photosynthetic reaction center

TLDR: In this paper, the photosynthetic reaction center (RC) was modeled as an octaalkyl- substituted zinc porphyrin (MJ) subunit with octa-alkyl substituted zinc (Z) pigments.

Abstract: Phenylene-bridged zinc diporphyrin (D)-monoporphyrin (h4)-pyro- mellitimide (I) triads were prepared as models for the photosynthetic reaction center (RC). With D and I fmed, the central monoporphyrin subunit is tuned from octaalkyl- substituted zinc porphyrin (MJ to a doubly strapped metal-free porphyrin (SH), a p- unsubstituted metal-free porphyrin (H), and a p-unsubstituted zinc porphyrin (Z) in order to achieve a RC-type sequential ET relay. In &%-I and D-SH-I, the charge separation (CS) between 'M,,* and I or 'SH* and I and a subsequent hole transfer to D provide D+-&--I' and IT-SH-I-, respectively. Upon excitation of D-H-I, an effective CS between the porphyrin pigments provides D+-H--I which is converted to D+-H-I by a subsequent charge shift reaction in 0.8 overall quantum yield in a manner analogous to that in RC. D-Z-I gives D+-Z-I in 0.4 overall quantum yield both in DMF and THF but the transient absorption spectra revealed that a stepwise ET relay of 'P-2-1 -+ IT-Z-I +D+-Z-I in DMF, while superexchange mediated long-distance electron transfer is suggested in THF.