Hot under the surface: Surfactants with purely inorganic head groups, comprising a ruthenium‐substituted polyoxotungstate cluster, are used to unlock the enormous potential of a synergistic combination of surfactant self‐assembly and stimuli‐responsive properties. The system can dynamically respond to a chemical trigger (such as a change in micelle shape; see scheme), and could lead to new applications for surfactants in light harvesting.

The interactions between molecular compounds and functionalized surfaces are omnipresent in many areas. For example, they are of crucial importance in all chromatographic processes using porous hosts. Developing a thorough understanding about the complex interplay of molecular scale processes involved in surface interactions is an issue of current scientific activity. In the present paper we discuss ESR spectroscopy as a powerful and easy to apply tool for examining host–guest effects within mesoporous materials. The method is tested for a series of modified, mesoporous materials comprising different surface functionalities like amine groups, carboxy groups, and others. There is a characteristic influence on the rotational characteristics of a molecular nitroxide spin probe. From temperature dependent data one can derive key thermodynamic parameters like interaction enthalpies. It is possible to differentiate (qualitatively and quantitatively) between mobile spin probes interacting mainly with the solvent and immobile guests interacting mainly with the surfaces. The polarity difference Δp v between solvent and pore-surface determines if molecular guests are in a free and highly mobile, interacting but still mobile, or interacting and immobilized state. It is interesting to note that immobilization takes place even for moderate Δp v values no matter if the surface is polar or unpolar. However, the behavior changes if there is a chemically specific interaction between the functional groups of the guests with a functionalized surface. Based on the systematic effect of the pore size on the rotational dynamics of the spin probe a qualitative model is proposed that includes a characteristic distance between confined guest species and pore surface as a function of the interaction strength.

Inorganic solids with porosity on the mesoscale possess a high internal surface area and a well‐accessible pore system. Therefore, it is a relevant task to equip the surfaces of such materials with a maximum density of various organic functional groups. Among these functions it is the capability of coordinating to metal species as a ligand that is of extraordinary importance in many areas, for example, in catalysis. This paper describes how prominent ligands containing donor functions such as carboxylic, thio, chelating, or amine groups can be obtained in the form of nanoporous organosilica materials. The coordination of metal centers such as CoII, MnII, VIV, or PtIV is studied in detail. The magnetic properties of the corresponding materials and some applications in catalysis are reported. A quantitative determination of the surface density of donor atoms by distance measurements using EPR spectroscopy is shown.

Mass transport of molecular compounds through porous solids is a decisive step in numerous, important applications like chromatography or heterogeneous catalysis. It is a multi-scale, hierarchical phenomenon: macrodiffusion (>μm) is influenced, in addition to parameters like grain boundaries and particle packing, by meso-scale (>10 nm, <μm) factors like particle size and the connectivity of pores. More importantly, meso-scale diffusion and macro-scale diffusion are first and foremost determined directly by processes on the molecular scale (<10 nm), which depend on numerous factors like pore-size, interactions of the host with the solid surfaces and with the solvent. Due to the high complexity of the latter and the fact that current analytical techniques enable only limited insights into solvent-filled pores with sufficient spatial and temporal resolution, the knowledge about the molecular origins of diffusive processes in porous materials is still restricted. The main focus of the current paper is on the development of continuous wave (CW) electron paramagnetic resonance (EPR) spectroscopy into a tool shedding some new light on molecular diffusion inside mesoporous silica materials differing systematically in pore size and surface functionalities. The advantages of CW-EPR are that its spatial resolution fits ideally to the size of mesopores (2-10 nm), it is fast enough for spotting molecular processes, and any conventional solvent and the porous matrix are EPR silent. Diffusion coefficients have been calculated considering spin exchange occurring from the diffusive collision of radicals, and are compared to complementary analytical techniques like MAS PFG NMR (sensitive for meso-scale) and EPR-imaging (sensitive to macroscale diffusion). Our results show that the choice of surface bound functional groups influences diffusion much stronger than pore-size. There are indications that this is not only due to different guest-surface interactions but also due to an altered mobility within the solvent under confinement.

The existence of more than one functional entity is fundamental for materials, which are desired of fulfilling complementary or succeeding tasks. Whereas it is feasible to make materials with a homogeneous distribution of two different, functional groups, cases are extremely rare exhibiting a smooth transition from one property to the next along a defined distance. We present a new approach leading to high-surface area solids with functional gradients at the microstructural level. Periodically ordered mesoporous organosilicas (PMOs) and aerogel-like monolithic bodies with a maximum density of azide groups were prepared from a novel sol-gel precursor. The controlled and fast conversion of the azide into numerous functions by click chemistry is the prerequisite for the implementation of manifold gradient profiles. Herein we discuss materials with chemical, optical and structural gradients, which are interesting for all applications requiring directionality, for example, chromatography.

Whereas size effects have been investigated extensively and are largely understood, it is significandy more challenging to elucidate how functional properties of semiconductors can be altered and ultimately be improved by a hierarchical nanoarchitecture. For semiconductor applications, such as in photovoltaics or photocatalysis, it is of great importance to learn how to avoid the recombination of photogenerated charge carriers and how to enhance their lifetime. A gas phase synthesis method is explored, which enables the generation of spherical zinc oxide nanostructures with compact, mesoporous, a special type of core-shell, so c;;alled yolk-shell, or hollow character. The particles with hollow character exhibit an :m extraordinarily long persistence of photogenerated charge carriers. It is demonstrated that the presence of the ZnO shell and its special orientation with respect to the polar character of the wu:rtzite lattice represent deciding factors. After photoexcitation, • OOOOOOOOOO electrons and holes migrate to opposite sides of the interfaces, where they are stabilized Moreover, photoluminescence thermometry was used to determine the thermal conductivity of the samples, which is lowered by a factor of,.., 100 compared with bulk ZnO. The thermal conductivity of this type of nanostructure is found to be only 10 times larger than that of air, and this points toward potential applications as thermoelectrics .• INTRODUGION Ceramic semiconductors continue to attract strong interest because they play a major role in many contemporary applications. For example, m;v compounds like GaN are currendy revolutionizing lighting technologies (LEDs) 1 and ll/ VI com~ounds are applied for UV protection/ in photovoltaic devices, ' 4 or as photocatalysts, for example, for the catalytic splitting of water or waste treatment. 5 -7 The performance of many of these devices depends critically on the ability of the semiconductors to generate excitonic charge carriers ( elec tron-hole pairs) when irradiated with light, as well as on the persistence of those photogenerated charge carriers (PGCCs).Thus, it is r:i prime importance to understand how the lifetime of these PGCCs is affected by the s~cific properties of the materials and how it can be controlled. The latter still remains a substantial challenge since the actual persistence of PGCCs depends strongly on numerous factors such as the coverage with stabilizers or other compounds, the density of intrinsic and extrinsic defects and, last but not least, the hierarchical construction of the material from the nanometer to the macroscopic scale. The structural motifs themselves evolve to a large extent from kinetic factors and are determined by the interplay of many parameters, which differ during the material 4593 syntheses. Unfortunately, it is very cumbersome to elucidate systematic coherences, when every material requires a different synthesis strategy. 9 -12 Nevertheless, the idea is highly tempting that the persistence of PGCCs could be controlled via the synthesis...

The bottom-up synthesis of functional materials has become one of the most versatile tools of nanochemistry. It requires not only control over composition and particle size, but also over shape. The fine-control over shape demands an in-depth knowledge about the nucleation and growth of inorganic crystals in the homogeneous phase. A detailed, mechanistic study about the crystallization of zinc oxide is presented here. The findings can easily be transferred to other binary solids with significant ionic character and in particular to those adopting polar crystal classes. New insights about the role of anionic capping agents, cations and kinetic factors during crystallization are reported. One has to conclude that the influence of the cations, specifically the interplay between cation and anion is more significant than expected. Furthermore, low-molecular weight additives containing carboxylic groups are compared to macromolecular additives leading to unusual mesocrystals. Similarities to the concepts of biomineralization are discussed. Finally, a drastic enhancement of photocatalytic activity by several orders of magnitude could be observed for shape-engineered ZnO nanoparticles.

We used spatially and time-resolved electron paramagnetic resonance (EPR) spectroscopy to study diffusion of guest molecules within solvent filled aerogel monoliths. We experimentally obtained the time-dependent spin density of EPR active guest molecules ρ 1d (y,t), numerically solved the diffusion equation to simulate ρ 1d (y,t), and determined the macroscopic translational diffusion coefficients for different aerogels and guest molecules. Simultaneously, we determined the microscopic diffusion coefficient by spectral simulation. We show that diffusion in the aerogels under study is dominated by the tortuosity of the pore system but not by surface effects.