Time‐Resolved EPR Spectra of Short Biradicals (1,3‐ to 1,8‐) in Solution. The Interconnecting Roles of the External Magnetic Field, Dipolar Coupling, Exchange Interaction, and Molecular Motion in the Spin Polarization and Relaxation Mechanisms.

Time-resolved electron paramagnetic resonance spectra of biradicals in solution with chain lengths of 3-8 carbon atoms are reported. Spin polarization arises from the spin-correlated radical pair (SCRP) mechanism and in some cases also from the triplet mechanism (TM). The observation of spectra at two magnetic fields, Z-band (3315 G) and Q-band (12 500 G), provides qualitative estimates of the relative importance of each mechanism for a given biradical. The influence of several magnetic properties, such as the spin-spin coupling J, the dipolar coupling D, and the electron-nuclear hyperfine interactions a H , on the time dependence and spectral shape is discussed