Continuous-Wave (CW) Photo-CIDNP NMR Spectroscopy: A Tutorial

Photo-chemically induced dynamic nuclear polarisation (photo-CIDNP) is a nuclear spin-selective magnetic resonance phenomenon that has traditionally been used to mechanistically study chemical reactions involving the (transient) formation of radical molecular species, extract EPR observables of short-lived radicals, probe biomolecular structure and interactions and, less importantly, increase the sensitivity of a nuclear magnetic resonance (NMR) measurement. Recently, the introduction of significant methodological advances as well as the advent of benchtop NMR spectroscopy has rekindled interest in this technique, which-serendipitously discovered more than half a century ago-has, as of late, matured into a powerful, highly sensitive and extremely versatile NMR hyperpolarisation method. In this tutorial, aimed primarily at the nonexpert user, we provide practical information on how to plan, set up and perform one-dimensional ¹H and heteronuclear photo-CIDNP NMR experiments using a high-field NMR spectrometer and a continuous-wave (CW) illuminant. In particular, strategies for selecting the appropriate experimental setup are described, including aspects such as light source requirements, introduction of appropriate light coupling methods and photosensitiser selection. In addition, examples of suitable one-dimensional ¹H and heteronuclear photo-CIDNP pulse schemes are presented, photo-CIDNP-specific acquisition parameters-including the implementation of sequence commands required to trigger the light source-are explained, and 'hands-on' practical advice on photo-CIDNP sample preparation is provided. Finally, special attention as to how to acquire and analyse one-dimensional photo-CIDNP data in a meaningful way is given.