Laser excitation combined with time-resolved CW-EPR spectroscopy of a carotenoid-porphyrin-diquinone tetrad (
1), observes polarized spectra of the end quinone radical anion, Q·
B
−. These spectra strongly depend on the time interval between the laser pulse and the position of the detection window of the
transient magnetization profile, and may lead to misinterpretation of the radical intermediates participating in the reaction
route. Spectral distortions arise from small hyperfine splittings and narrow line widths, resulting in the appearance of Torrey
wiggles at off-resonance fields. The correct spectrum, however, and its line shape appear at times above 1 μs after the laser
pulse, and is in complete agreement with the Fourier transform EPR spectrum. Analysis and reconstruction of the transient
spectra is carried out in Fourier conjugate space. The experimental spectra are shown to be the Fourier transform of the free-induction
decay (FID) multiplied by an appropriate windowing function. The changes in the spectra taken at t<1 μs are due to line distortions
and not to chemical processes. This treatment is of general applicability in the spectral analysis of time-resolved CW-EPR
spectra.