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

Guoquan Liu,Igor Tkach,Shu-Hao Liou,Nikolay Enkin,Marina Bennati

doi:10.1039/c7cp06073d

Abstract

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.

Highlights

Dynamic nuclear polarization (DNP) is a rapidly developing method to enhance the sensitivity of nuclear-magnetic resonance (NMR) techniques.[1]
DNP in liquids is based on electron–nuclear cross relaxation, the so-called Overhauser effect, and the NMR signal enhancement e is well described by the following equation:[3,4,5] e = 1 À seffÁfÁxÁ|ge|/gI
The results provide a frame to optimize the performance of polarizers for Optically-driven DNP (ODNP) and pave the way for more systematic investigations

Summary

Introduction

Dynamic nuclear polarization (DNP) is a rapidly developing method to enhance the sensitivity of nuclear-magnetic resonance (NMR) techniques.[1] The method transfers spin polarization from electrons to coupled nuclear spins by microwave (MW) irradiation. For electron spins in thermal equilibrium prior to MW pumping, NMR signal enhancements up to 3 orders of magnitude have been reported,[2] with a theoretical limit determined by the gyromagnetic ratios g of electrons and nuclear spins (for 1H: |ge|/gH = 658). DNP in liquids is based on electron–nuclear cross relaxation, the so-called Overhauser effect, and the NMR signal enhancement e is well described by the following equation:[3,4,5] e = 1 À seffÁfÁxÁ|ge|/gI (1).

Methods

Results

Conclusion