Time-resolved EPR investigation of [70]fulleropyrrolidine nitroxide isomers

A novel [70]fulleropyrrolidine functionalized with a nitroxide radical has been synthesized. After pulsed photoexcitation, time-resolved electron paramagnetic resonance (EPR) spectra have been recorded in liquid solution at standard X-band (9.5 GHz) and W-band (95 GHz) microwave frequencies. The spectra exhibit strongly electron spin polarized ground and excited states, the latter being arising from the spin coupling of the nitroxide's electron spin with the fullerene's excited triplet state. The EPR parameters such as g-values and hyperfine coupling constants have been discussed in terms of the spin Hamiltonian for excited doublet, triplet and quartet states. On the basis of the strength of the exchange interaction between the fullerene triplet and the radical group, two, out of a possible four [70] fulleropyrrolidine isomeric monoadducts, have been characterized.