Fourier Transform EPR Measurement of Homogeneous Electron Transfer Rates

Fourier‐Transform Electron Paramagnetic Resonance has measured the rates of homogeneous electron transfer reactions involving duroquinone radical anions. The radicals are generated by laser photolysis of duroquinone in methanol solution containing 10% triethylamine. The duroquinone concentration was varied over a factor of 1000. The rate constant for electron transfer between the radical anion and the neutral duroquinone is 1.5×108M−1s−1 and the intrinsic spin relaxation rates, T−11 and T−12 are 0.32 MHz and 0.44 MHz, respectively. Two‐Dimensional magnetization transfer spectra show that the reaction is a homogeneous electron transfer reaction. The electron transfer rates are measured by two novel pulse sequences designed for more efficient data acquisition in samples with no unresolved inhomogeneous broadening. These two sequences result in a more rapid, accurate determination of the second‐order chemical rate constant since the second‐order rate constant is obtained directly and is not derived from a single measurement of a pseudo‐first‐order rate. The transient duroquinone radical anions studied here appear to have the same T1, T2 and electron transfer rates as stable duroquinone radical anions in alkaline solutions.