Spin-Polarized Radical Ion Pair Formation Resulting from Two-step Electron Transfer from the Lowest Excited Singlet State of a Fixed-Distance Photosynthetic Model System at 5 K
- 1 January 1991
- journal article
- research article
- Published by Taylor & Francis in Molecular Crystals and Liquid Crystals
- Vol. 194 (1), 201-207
- https://doi.org/10.1080/00268949108041165
Abstract
A photosynthetic reaction center model consisting of a zinc porphyrin primary electron donor, ZP, positioned between a naphthoquinone electron acceptor, NQ, and an N,N,N,N–tetraalkyl–p–phenylenediamine secondary electron donor, TAPD, was synthesized. The resulting rigid structure places the TAPD donor at a fixed 23 Å center–to–center distance from the NQ acceptor. Excitation of ZP with 540 nm light in butyronitrile glass at 5 K results in two–step sequential electron transfer: TAPD–1*ZP–NQ > TAPD–ZP+−NQ− −> TAPD+−ZP–NQ−. The final TAPD+−ZP–NQ− radical pair lives for 4 ms and exhibits a spin–polarized EPR spectrum characteristic of a spin–correlated radical pair. The EPR spectrum of this long–lived, spin–polarized radical ion pair closely mimics the bacteriochlorophyll cation – quinone anion radical pair produced in photosynthetic reaction centers.Keywords
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