Strong modulation of the exchange interaction in a spin-polarized, aryl ether-linked 1,14-biradical

The time-resolved electron paramagnetic resonance spectrum of a 1,14-bis(alkyl)biradical linked via the para position of an aryl ether moiety has been studied. Previously the spectrum obtained at 50 degrees C could not be simulated using spin-correlated radical pair (SCRP) theory. It is successfully simulated here by adding modulation of the exchange interaction (J) to the fitting routine as a T-2 relaxation mechanism. Inclusion of this Line-broadening effect allowed an accurate value of the exchange interaction to be determined for this temperature. Comparison of this J value with that obtained in previous work for the meta isomer of the same biradical showed that the dominant mechanism of J coupling is through-solvent rather than through-bond. The magnitude of the J modulation matrix elements in the two isomers are discussed as are their temperature dependencies.