Abstract
Photo-CIDNP (photo-chemically induced dynamic nuclear polarization) refers to nuclear polarization created by the spin-chemical evolution of spin-correlated radical pairs (SCRPs). This phenomenon occurs in gases, liquids and solids. Based on the solid-state photo-CIDNP effect observed under magic-angle spinning (MAS), photo-CIDNP MAS NMR has been developed as analytical method. Here we report the origin, the theory and the state of the art of this method.
Highlights
Induced Dynamic Nuclear Polarization (CIDNP) is a phenomenon in spin-chemistry [1–3], which is a sub-field of chemistry dealing with the role of spin degrees of freedom in chemical reactions
Spin-chemistry phenomena originate from the fact that many chemical reactions are electron-spin selective, i.e., they occur at different rates for reactants in different electron spin states
The effect of nuclear spins on chemical reactions is typically not expected, since the energy associated with spin state changes is extremely small, the unexpected discoveries of Chemically Induced Dynamic Nuclear Polarization (CIDNP) and the magnetic isotope effect clearly demonstrate their crucial role
Summary
Induced Dynamic Nuclear Polarization (CIDNP) is a phenomenon in spin-chemistry [1–3], which is a sub-field of chemistry dealing with the role of spin degrees of freedom in chemical reactions. A further challenge is that spin-sorting mechanism that rely on differences in the chemical reactivity of the radical pair in its different electronic spin states to produce photo-CIDNP effects are not expected to be operative in solids This is because the radical centers, which constitute the radical pair, cannot separate by molecular diffusion, as would be the case in liquids or solutions. The theoretical explanation [6–9] has been based on several models, valid for different particular cases, which make use of special assumptions about either the chemical reactivity and fate of polarization in different reaction channels or the presence of anisotropic spin interactions Until recently, such a treatment has remained disconnected from the well-established liquid-state CIDNP theory [10–15]. Suitable systems can be either rigid [45, 46] or flexible [42–44, 47] biradicals
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