Photo-induced radical polarization and liquid-state dynamic nuclear polarization using fullerene nitroxide derivatives.

We report on radical polarization and optically-driven liquid DNP using nitroxide radicals functionalized by photoexcitable fullerene derivatives. Pulse laser excitation of the fullerene moiety leads to transient nitroxide radical polarization that is one order of magnitude larger than that at the Boltzmann equilibrium. The life time of the radical polarization increases with the size of the fullerene derivative and is correlated with the electronic spin-lattice relaxation time T1e. Overhauser NMR signal enhancements of toluene solvent protons were observed under steady-state illumination, which replaced microwave irradiation.