Fourier transform EPR study of N-centered pyrimidine radicals in the nanosecond time-scale

Using nanosecond laser photolysis with 308 nm and Fourier transform EPR spectroscopy, the pyrimidine radicals (thymine, uracil and 6-methyluracil) generated by electron transfer from the pyrimidine ground state to spin-polarized anthraquinone-2,6-disulfonate (2,6-AQDS) triplets were studied. The pyrimidine radical cations decay by deprotonation at the N(1) position to the neutral pyrimidine-1-yl radical. No other reaction channel could be found. The rate constant of the electron transfer could be estimated from the triplet spin-polarization (CIDEP) of the 2,6-AQDS radical anions to: ket(thymine) = 4.1 × 109 M−1 s−1, ket(uracil) = 2.4 × 109 M−1 s−1 and ket(6-methyluracil) = 4.5 × 109 M−1 s−1.