The random motion (the diffusion) of guest molecules in nanoporous host materials is key to their manifold technological applications and, simultaneously, a ubiquitous phenomenon in nature quite in general. Based on a specification of the different conditions under which molecular diffusion in nanoporous materials may occur and of the thus resulting relevant parameters, a survey of the various ways of the measurement of the determining parameters is given. Starting with a condensed introduction to the respective measuring principles, the survey notably includes a summary of the various parameters accessible by each individual technique, jointly with an overview of their strengths and weaknesses as well as of the respective ranges of observation. The presentation is complemented by basic relations of diffusion theory and molecular modeling in nanoporous materials, illustrating their significance for enhancing the informative value of each measuring technique and the added value attainable by their combination. By providing guidelines for the measurement and reporting of diffusion properties of chemical compounds in nanopores, the document aims to contribute to the clarification and standardization of the presentation, nomenclature, and methodology associated with the documentation of diffusion phenomena in nanoporous materials serving for catalytic, mass separation, and other relevant purposes.

Adenosine triphosphate (ATP) and other nucleotides can be irreversibly bound to the metal-organic framework (MOF) MIL-101(Cr). Analysis of X-ray diffraction data suggests that the location of the adsorbed ATP molecule is in proximity of the Cr3 clusters. Solid-state NMR and DFT calculations indicate that ATP is bound to MIL-101(Cr) through linkages of the terminal phosphate group with Cr(III) of the framework. In the presence of Cu(II) ions, the MOF-supported nucleotides can function as stable and reusable enantioselective heterogeneous catalysts for reactions like Diels-Alder and Michael addition. Compared to the corresponding homogeneous nucleotide-based artificial metalloenzymes (ArMs), the MOF-supported nucleotide-based ArMs exhibit significantly enhanced activity and selectivity in certain cases, demonstrating their potential as a new class of enantioselective heterogeneous catalysts.

The compositions and structures of the conjugated polymer poly(2,5-bis(3-hexadecylthiophen-2-yl)thienothiophene) (PBTTT-C-16) are quantitatively measured and distinguished for the crystalline and disordered regions, as well as the intermolecular interactions between phenyl-C-71-butyric acid methyl ester (PC71BM) and PBTTT moieties in bulk heterojunctions (BHJs). For PBTTT-C-16, the long-range (>10 nm) crystalline order of lamellae is established by two-dimensional (2D) grazing-incidence small-angle X-ray scattering (GISAXS), while short-range (<1 nm) structures are characterized by using solid-state nuclear magnetic resonance (NMR) spectroscopy. In particular, 2D H-1{H-1} double-quantum and C-13{H-1} heteronuclear correlation NMR spectra reveal distinct intensity correlations for PBTTT-C-16 that provide direct evidence for the presence of regions with well-ordered pi-pi-stacked conjugated backbones and interdigitated alkyl side chains, stacked backbones and disordered side chains, and amorphous regions of PBTTT-C-16. Good agreement is found between the X-ray diffraction (XRD) and solid-state NMR analyses for H-1-H-1 distances between interlayer aromatic moieties (3.7 & Aring; from XRD, 3.6 & Aring; from 2D H-1{H-1} NMR) and for the intermolecular C-H distances between the aromatic hydrogen atoms and terminal methyl carbon atoms (3.3-3.4 & Aring; from XRD, 3.3 & Aring; from 2D C-13{H-1} NMR) in the crystalline regions. A larger mean H-1-H-1 distance of >3.8 & Aring; between interlayer PBTTT backbones in less-ordered and disordered regions is determined by NMR, which is otherwise difficult to assess by XRD analyses alone. Combined solid-state NMR and density functional theory (DFT) results corroborate that the conjugated PBTTT-C-16 backbones adopt nearly coplanar conformations in the ordered regions with a distribution of dihedral angles bisecting the thienothiophene moieties in the amorphous regions. The polar five-membered ring of the C-70 fullerene in the PBTTT-C-16:PC71BM blend was found to interact strongly with the aromatic thienothiophene protons of the semiconducting polymer, causing a strong pi-pi overlap of distinct moieties of the fullerene and polymer chain. The relative displacements of H-1 chemical shifts by local ring currents and measurements of homonuclear H-1 dipole-dipole couplings allow the molecular proximities between specific chemical moieties of the electron-donating PBTTT and the electron-accepting PC71BM species in the bimolecular BHJs to be established.

Semiconducting polymers provide a ubiquitous platform for a range of applications in molecular electronics and photovoltaics, but the ordered and disordered regions of these materials impart different optoelectronic properties. By resolving local morphology using solid-state magnetic resonance spectroscopy and modeling techniques, here, we demonstrate that the PTB7-Th donor-acceptor (D-A) copolymer and P3HT and MEH-PPV homopolymers exhibit different degrees of the short-range order, which can be associated with the large differences in their charge carrier mobilities. The high degree of local order in PTB7-Th (84-99%) is facilitated by noncovalent interactions between D and A moieties. In contrast to this, the reduced local order in P3HT (30-44%) and MEH-PPV (39-43%) homopolymers is due to the distortions in the vicinities of backbone and side chain moieties that lead to conformationally tilted polymer chains. Combined solid-state NMR and density functional theory (DFT) modeling allows the degree of backbone torsion in these materials to be determined, and insights into packing interactions are obtained by two-dimensional (2D) H-1-H-1, H-1-C-13, and H-1-F-19 correlation NMR spectroscopy. In addition, the different paramagnetic species and hyperfine interactions are analyzed by EPR spectroscopy and are expected to influence the charge carrier mobilities. A detailed analysis of the local structures presented in this study helps explain the morphological anomalies and their impact on bulk charge carrier mobilities and electronic density of states, thus providing essential insights into the morphology-property relationships in polymeric organic semiconductors.

Disordered proteins often undergo a stimuli-responsive, disorder-to-order transition which facilitates dynamic processes that modulate the physiological activities and material properties of cells, such as strength, chemical composition, and reflectance. It remains challenging to gain rapid and spatiotemporal control over such disorder-to-order transitions, which limits the incorporation of these proteins into novel materials. The reflectin protein is a cationic, disordered protein whose assembly is responsible for dynamic color camouflage in cephalopods. Stimuli-responsive control of reflectin's assembly would enable the design of biophotonic materials with tunable color. Herein, a novel, multivalent azobenzene photoswitch is shown to be an effective and non-invasive strategy for co-assembling with reflectin molecules and reversibly controlling assembly size. Photoisomerization between the trans and cis (E and Z) photoisomers promotes or reduces Coulombic interactions, respectively, with reflectin proteins to repeatedly cycle the sizes of the photoswitch-reflectin assemblies between 70 nm and 40 nm. The protein assemblies formed with the trans and cis isomers show differences in interaction stoichiometry and secondary structure, which indicate that photoisomerization modulates the photoswitch-protein interactions to change assembly size. Our results highlight the utility of photoswitchable interactions to control reflectin assembly and provide a tunable synthetic platform that can be adapted to the structure, assembly, and function of other disordered proteins.

Knowledge of the mechanism by which polymorphic inorganic species, such as carbonates, are formed is crucial to understand and guide the selective crystallization of end products. Recently it has been shown that a key step in the crystallization of calcium carbonate is the formation of intermediate species known as prenucleation clusters. However, the observation of these prenucleation clusters in solution is exceedingly challenging because of their short lifetime and low concentrations. Here, using dissolution DNP-enhanced NMR spectroscopy, we observe signals from prenucleation species of calcium carbonate from which the kinetics of formation and conversion are determined.

Strong metal-support interactions (SMSIs) are well-known in the field of heterogeneous catalysis to induce the encapsulation of platinum (Pt) group metals by oxide supports through high temperature H2 reduction. However, demonstrations of SMSI overlayers have largely been limited to reducible oxides, such as TiO2 and Nb2O5. Here, we show that the amorphous native surface oxide of plasmonic aluminum nanocrystals (AlNCs) exhibits SMSI-induced encapsulation of Pt following reduction in H2 in a Pt structure dependent manner. Reductive treatment in H2 at 300 °C induces the formation of an AlOx SMSI overlayer on Pt clusters, leaving Pt single-atom sites (Ptiso) exposed available for catalysis. The remaining exposed Ptiso species possess a more uniform local coordination environment than has been observed on other forms of Al2O3, suggesting that the AlOx native oxide of AlNCs presents well-defined anchoring sites for individual Pt atoms. This observation extends our understanding of SMSIs by providing evidence that H2-induced encapsulation can occur for a wider variety of materials and should stimulate expanded studies of this effect to include nonreducible oxides with oxygen defects and the presence of disorder. It also suggests that the single-atom sites created in this manner, when combined with the plasmonic properties of the Al nanocrystal core, may allow for site-specific single-atom plasmonic photocatalysis, providing dynamic control over the light-driven reactivity in these systems.

Brønsted acidic zeolites are ubiquitous catalysts in fuel and chemical production. Broadening the catalytic diversity of a given zeolite requires strategies to manipulate the acid site placement at framework positions within distinct microporous locations. Here, we combine experiment and theory to elucidate how intermolecular interactions between organic structure-directing agents (OSDAs) and framework Al centers influence the placement of H+ sites in distinct void environments of MFI zeolites and demonstrate the catalytic consequences of active site location on kinetically controlled (403 K) toluene methylation to xylene regioisomers. Kinetic measurements, interpreted using mechanism-derived rate expressions and transition state theory, alongside density functional theory (DFT) calculations show that larger intersection environments similarly stabilize all three xylene isomer transition states without altering well-established aromatic substitution patterns (ortho/para/meta ∼ 60%:30%:10%), while smaller channel environments preferentially destabilize transition states that form bulkier ortho- and meta-isomers, thereby resulting in high intrinsic para-xylene selectivity (∼80%). DFT calculations reveal that the flexibility of nonconventional OSDAs (e.g., 1,4-diazabicyclo[2.2.2]octane) to reorient within MFI intersections and their ability to hydrogen-bond to form protonated complexes favor the placement of Al in smaller channel environments compared to conventional quaternary OSDAs (e.g., tetra-n-propylammonium). These molecular-level insights establish a mechanistic link between OSDA structure, active site placement, and transition state stability in MFI zeolites and provide active site design strategies that are orthogonal to crystallite design approaches harnessing complex reaction-diffusion phenomena to enhance regioisomer selectivity in the industrial production of valuable polymer precursors.

Inorganic–organic mesophase materials provide a wide range of tunable properties, which are often highly dependent on their nano‐, micro‐, or meso‐scale compositions and structures. Among these are macroscopic orientational order and corresponding anisotropic material properties, the adjustability of which are difficult to achieve. This is due to the complicated transient and coupled transport, chemical reaction, and surface processes that occur during material syntheses. By understanding such processes, general criteria are established and used to prepare diverse mesostructured materials with highly aligned channels with uniform nanometer dimensions and controllable directionalities over macroscopic dimensions and thicknesses. This is achieved by using a micropatterned semipermeable poly(dimethylsiloxane) stamp to manage the rates, directions, and surfaces at which self‐assembling phases nucleate and the directions that they grow. This enables mesostructured surfactant‐directed silica and titania composites, including with functional guest species, and mesoporous carbons to be prepared with high degrees of hexagonal order, as well as controllable orthogonal macroscopic orientational order. The resulting materials exhibit novel anisotropic properties, as demonstrated by the example of direction‐dependent photocurrent generation, and are promising for enhancing the functionality of inorganic–organic nanocomposite materials in separations, catalysis, and energy conversion applications.

Adenosine triphosphate (ATP) and other nucleotides can be irreversibly bound to the metal-organic framework (MOF) MIL-101(Cr). Analysis of X-ray diffraction data suggests that the location of the adsorbed ATP molecule is in proximity of the Cr3 clusters. Solid-state NMR and DFT calculations indicate that ATP is bound to MIL-101(Cr) through linkages of the terminal phosphate group with Cr(III) of the framework. In the presence of Cu(II) ions, the MOF-supported nucleotides can function as stable and reusable enantioselective heterogeneous catalysts for reactions like Diels-Alder and Michael addition. Compared to the corresponding homogeneous nucleotide-based artificial metalloenzymes (ArMs), the MOF-supported nucleotide-based ArMs exhibit significantly enhanced activity and selectivity in certain cases, demonstrating their potential as a new class of enantioselective heterogeneous catalysts.

A combination of nonionic, cationic, and zwitterionic surfactants is shown both to stabilize the transmembrane protein proteorhodopsin, as well as to direct coassembly into robust transparent mesostructured silica-surfactant films containing high loadings of functionally active protein guests. Proteorhodopsin is a transmembrane protein that exhibits light-activated H+ transport properties, the photocycle kinetics of which are quantified by time-resolved UV-visible spectroscopy and demonstrated to be similar to proteorhodopsin in the abiotic mesostructured films compared to native-like lipids. The surfactants mediate the pK(a) of a key ion-channel residue, leading to an expanded pH functional range for proteorhodopsin in mesostructured silica-surfactant host materials. Small-angle X-ray diffraction results for 100-mu m films show high extents of mesoscale order with protein loadings up to 25 wt % and wormlike mesostructural order for 44 wt % proteorhodopsin. Solid-state H-1, C-13, and Si-29 NMR analyses provide atomic-scale insights into the compositions and interactions at the mesochannel surfaces, which account for the structure-directing roles of surfactant species. Nanoindentation measurements reveal the mechanical robustness of the films, which interestingly increases with proteorhodopsin loading for the compositions examined. Heat treatment analyses show improved thermal stability for proteorhodopsin to 110( degrees)C within mesostructurally ordered films. The results establish closely correlated relationships between the compositions, nano- and mesoscale structures, photocycle kinetics, and macroscopic mechanical properties and thermal stabilities of the silica-surfactant- proteorhodopsin films, providing key biomimetic design criteria.

We report herein a detailed study on the influence of hydrothermal treatment temperature on both long- and short-range structures of SnO2 nanoparticles (NPs) applied as photocatalysts for the discoloration of organic pollutants and as photoanodes for water splitting. Synchrotron X-ray diffraction and X-ray absorption near-edge spectroscopy measurements confirmed the enhancement of the structural order of SnO2 NPs as a function of hydrothermal temperature. Fourier transform infrared spectroscopy revealed that the hydrothermal treatment increased the amount of hydroxyl groups on the SnO2 NPs surface. Regarding the photocatalytic activity, the NPs were able to promote the discoloration of different dyes that can act as potential organic pollutants. The photoelectrocatalytic performance of the samples depended on the hydrothermal treatment temperature, with the degree of crystallinity and surface hydroxyl groups playing a significant role in their performance as photoanodes. In particular, the NPs treated at a higher temperature presented a better degree of crystallinity, in addition to many hydroxyls on their surface, leading to increased mobility of the photogenerated charge carriers and improving the interaction between the molecules degraded and the material surface. The results demonstrated that the hydroxyls adsorbed on the SnO2 surface favor the formation of hydroxyl radicals, a species that indirectly participate in the photocatalytic oxidation of rhodamine B dye. The photoelectrocatalytic tests showed that the NPs treated at 200 °C increased oxygen evolution reaction performance.

The distributions of heteroatoms within zeolite frameworks have important influences on the locations of exchangeable cations, which account for the diverse adsorption and reaction properties of zeolite catalysts. In particular for aluminosilicate zeolites, paired configurations of aluminum atoms separated by one or two tetrahedrally coordinated silicon atoms are important for charge-balancing pairs of H+ cations, which are active for methanol dehydration, or divalent metal cations, such as Cu2+, which selectively catalyze the reduction of NOx, both technologically important reactions. Such paired heteroatom configurations, however, are challenging to detect and probe, due to the typically nonstoichiometric compositions and nonperiodic distributions of aluminum atoms within aluminosilicate zeolite frameworks. Nevertheless, distinct configurations of paired framework aluminum atoms are unambiguously detected and resolved in solid-state 2D 27Al-29Si and 29Si-29Si NMR spectra, which are sensitive to the local environments of covalently bonded 27Al-O-29Si and 29Si-O-29Si moieties, respectively. Specifically, two H+-chabazite zeolites with the same bulk framework aluminum contents are shown to have different types and populations of closely paired aluminum species, which correlate with higher activity for methanol dehydration. The methodologies and insights are expected to be broadly applicable to analyses of heteroatom sites, their distributions, and adsorption and reaction properties in other zeolite framework types.

We report the photocatalytic activity of iron-grafted mesoporous Pt/TiO2 catalysts, combining the properties of heterojunction photocatalysts with mesopomsity, for the gas-phase production of hydrogen from water-ethanol mixtures. GC-MS analysis reveals a preferential ethanol dehydrogenation reaction pathway, resulting in the formation of acetaldehyde with high selectivity versus carbon dioxide, for all of the catalysts investigated. Multi-technique characterization reveals that, in all the iron-grafted samples, Fe is located predominantly on the surfaces of the catalysts as Fe2O3 rather than doping the anatase structure, while the mesoporosity of the starting TiO2 is preserved. Among the different materials, the activity for photocatalytic ethanol dehydrogenation is optimum in the catalyst with the lowest iron content. According to XPS and time-resolved fluorescence measurements, this can be accounted for by higher Fe surface dispersion and consequent efficient formation of a surface heterojunction between Fe2O3 and TiO2 that favours charge separation.

In this work, we discuss the synthesis and characterization of a 2D coordination polymer composed of a dianionic perhydroxylated boron cluster, [B12(OH)122-], coordinated to Zn(II)—the first example of a transition metal-coordinated [B12(OH)12]2- compound. This material was synthesized via cation exchange from the starting cesium salt and then subjected to rigorous characterizion prior to and after thermal activation. Numerous techniques, including XRD, FTIR, SEM, TGA, and solid-state NMR revealed a 2D coordination polymer composed of sheets of Zn(II) ions intercalated between planes of boron clusters. The as-synthesized material was then evacuated of solvent via thermal treatment, and atomic-level changes from this transformation were elucidated through a combination of 1D and 2D solid-state NMR analyses of 11B and 1H nuclei, suggesting the full removal of coordinated solvent molecules. Evidence also suggested that [B12(OH)122-] can adjust its coordination to Zn(II) in the solid-state through hemilability of its numerous -OH ligands.

We report on the reversible, electrochemical (de)fluorination of the defect fluoride pyrochlore CsMnFeF6 at room temperature using a liquid electrolyte. CsMnFeF6 was synthesized via three different methods (hydrothermal, ceramic, and mechanochemical), each of which yield products of varying particle size and phase purity. Using galvanostatic cycling, we found that after three oxidative/ reductive cycles, approximately one fluoride ion can be reversibly inserted and removed from mechanochemically synthesized CsMnFeF6 for multiple cycles. Ex-situ X-ray absorption spectroscopy confirmed that both the Mn2+ and Fe3+ in this composition are redox active during cycling. Electrochemical impedance spectroscopy and ex-situ synchrotron powder diffraction were utilized to investigate the delayed onset of significant fluoride (de)insertion. We observed decreased impedance after one full cycle and subtle expansion and contraction of the CsMnFeF6 cubic lattice on oxidation (insertion) and reduction (removal), respectively, over the first two cycles. Our results suggest the formation of fluoride vacancies in early cycles generates mixed-valent Fe that enhances the conductivity and improves the reversibility in later cycles.

Organic solar cells that are transparent to visible light are highly desirable for applications such as window treatments or solar greenhouse panels. A key challenge is to simultaneously transmit most photons between 400 and 700 nm while retaining a high short‐circuit current and power conversion efficiency (PCE). Here, organic bulk heterojunction (BHJ) solar cells consisting of a donor polymer (PM2) is reported and the non‐fullerene acceptor ITIC‐Th achieves a PCE of 9.3%, and the BHJ thin films exhibit an average visible transmittance over 40%. This value is achieved primarily due to a very high open‐circuit voltage (VOC) of 0.93 V, which represents a voltage loss of only 0.50 V relative to the material optical bandgap, Eopt. In PM2:PC61BM devices, this voltage loss increases to 0.62 V (VOC = 0.82 V). It is found that this difference in VOC is due to higher nonradiative recombination in the fullerene‐based solar cell, suggesting that non‐fullerene acceptors may lead to better performance in semi‐transparent devices. The optoelectronic properties associated with PM2:ITIC‐Th and PM2:PC61BM blends are further corroborated by different morphological features and local structures at the donor‐acceptor interfaces characterized by atomic force microscopy, X‐ray scattering, and solid‐state NMR spectroscopy techniques.

To understand the nature and structure of N-doping centers in carbon materials, we combine two-dimensional (2D) solid-state NMR experiments and chemical shift calculations for N-15, C-13, and H-1 nuclei from density functional theory (DFT). Comparisons of predicted chemical shifts with experimental 2D C-13-N-15 spectra show good agreement and the calculations explain the spectral broadening seen in the experiments. The major differences between the chemical shifts of graphitic/pyridinic/pyrrolic N-moieties are understood by comparing the electronegativities of the various environments. Moreover, the signal broadening is explained using four different factors: (1) the standalone N/C geometry, (2) the effect of a second N atom nearby, (3) the first or second neighbor C atom difference, and (4) the influence of residual water, which is important to understand the electrocatalytic environment. An intuitive correlation between the charge of the probed atom and the chemical shift is validated: the smaller the charge, i.e., higher electron density, the more shielded the nucleus is, and hence the smaller the associated chemical shift. These results can improve the understanding of the nature of heteroatom sites in nitrogen-carbon materials and contribute to the rational design of these materials with desired electronic properties and improved electrochemical performance.