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-b is(alkyl)biradical linked via the para position of an aryl ether moiet y has been studied. Previously the spectrum obtained at 50 degrees C c ould not be simulated using spin-correlated radical pair (SCRP) theory . It is successfully simulated here by adding modulation of the exchan ge interaction (J) to the fitting routine as a T-2 relaxation mechanis m. Inclusion of this Line-broadening effect allowed an accurate value of the exchange interaction to be determined for this temperature. Com parison of this J value with that obtained in previous work for the me ta 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 a s are their temperature dependencies.