Imaging Radial Distribution Functions of Complex Particles by Relayed Dynamic Nuclear Polarization

The physical properties of many modern multi-component materials are determined by their internal microstructure. Tools capable of characterizing complex nanoscale architectures in composite materials are, therefore, essential to design materials with targeted properties. Depending on the morphology and the composition, structures may be measured by laser diffraction, scattering methods, or by electron microscopy. However, it can be difficult to obtain contrast in materials where all the components are organic, which is typically the case for formulated pharmaceuticals, or multi-domain polymers. In nuclear magnetic resonance (NMR) spectroscopy, chemical shifts allow a clear distinction between organic components and can in principle provide the required chemical contrast. Here, we introduce a method to obtain radial images of the internal structure of multi-component particles from NMR measurements of the relay of nuclear hyperpolarization obtained from dynamic nuclear polarization. The method is demonstrated on two samples of hybrid core–shell particles composed of a core of polystyrene with a shell of mesostructured silica filled with the templating agent CTAB and is shown to yield accurate images of the core–shell structures with a nanometer resolution

Hammett Parameter in Microporous Solids as Macroligands for Heterogenized Photocatalysts

Here we present a series of heterogeneous catalysts based on metal–organic frameworks and microporous polymers used as macroligands for heterogenized organometallic complexes. We show that both homogeneous and heterogenized catalysts follow the same linear correlation between the electronic effect of the ligand, described by the Hammett parameter, and the catalytic activity. This correlation highlights the crucial impact of the local electronic environment surrounding the active catalytic center over the long-range framework structure of the porous support. The rational design of heterogenized catalysts can thus be guided by molecular chemistry rules. The conception of highly efficient heterogeneous catalyst based on porous polymer support and driven by the Hammett parameter of bipyridine-chelating macroligand is demonstrated here for the Rh-catalyzed photoreduction of carbon dioxide with turnover frequencies up to 28 h^–1, among the highest reported for heterogeneous photocatalytic formate production