Gaussian Free-Energy Dependence of Electron-Transfer Rates in Iridium Complexes

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Science  02 Mar 1990:
Vol. 247, Issue 4946, pp. 1069-1071
DOI: 10.1126/science.247.4946.1069


The kinetics of photoinduced electron-transfer (ET) reactions have been measured in a series of synthetic donor-acceptor complexes. The electron donors are singlet or triplet excited iridium(I) dimers (Ir2), and the acceptors are N-alkylpyridinium groups covalently bound to phosphinite ligands on the Ir2 core. Rate constants for excited-state ET range from 3.5 x 106 to 1.1 x 1011 per second, and thermal back ET (pyridinium radical to Ir2+) rates vary from 2.0 x 1010 to 6.7 x 107 per second. The variation of these rates with driving force is in remarkably good agreement with the Marcus theory prediction of a Gaussian free-energy dependence.

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