Comparison of Ultrafast Electron Transfers in Porphyrin-Quinone and Mg/Free-Base Diporphyrin Molecules: Mimicking Photosynthetic Charge Separations

摘要

The Mg-H sub 2 diporphyrin exhibits light driven, electron transfer (ET) kinetics and thermodynamic efficiencies comparable to those found in natural photosystems. Indeed, it is a good model of the initial charge separation in photosystem II of green plants where a ligated chlorophyll is the postulated electron donor and pheophytin (a metal-free chlorophyll) is the postulated acceptor. Also, comparing the light driven ETs in P sub 3 QP and Mg-H sub 2 illustrates the important role of nuclear distortions in controlling ET product lifetimes. The extreme instability of the exp 1 (P sub 3 Q exp - .P exp + .) intermediate suggests a reason for the apparent absence of quinones as primary electron acceptors despite their abundance in natural photosystems and their use as secondary ET agents. (ERA citation 06:023269)