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Hybrid perovskite materials are one of the most promising candidates for optoelectronic applications, e.g., solar cells and LEDs, which can be produced at low cost compared to established materials. Although this field of research has seen a huge upsurge in the past decade, there is a major lack in understanding the underlying processes, such as shape-property relationships and the role of defects. Our aerosol-assisted synthesis pathway offers the possibility to obtain methylammonium lead bromide (MAPbBr3) microcrystals from a liquid single source precursor. The differently shaped particles are aligned on several substrates, without using a directing agent or other additives. The obtained particles show good stability under dry conditions. This allows us to characterize these materials and their pure surfaces at the single-crystal level using time- and spatially resolved methods, without any influences of size-dependent effects. By optimizing the precursor for the aerosol process, we were able to eliminate any purification steps and use the materials as processed. In addition, we performed theoretical simulations to deepen the understanding of the underlying processes in the formation of the different crystal facets and their specific properties. The model system presented provides insights into the shape-related properties of MAPbBr3 single crystals and their directed but ligand-free synthesis. [ABSTRACT FROM AUTHOR]

Nanostructured metamaterials can offer optical properties beyond what is achievable in conventional media, such as negative refraction or sub‐wavelength imaging. Due to their structural anisotropy, the class of high aspect ratio metamaterials is of interest for the possibility of achieving hyperbolic optical properties, i.e., both metallic and dielectric behavior based on the excitation direction. Although investigated numerically, the fabrication of tailor‐made metamaterials is complex or often beyond the reach of current technology. For wire metamaterials composed of aligned metallic nanowires in a dielectric matrix, since the free carrier concentration in metals is fixed, light‐matter interaction cannot be adjusted after fabrication. Here, metamaterials based on plasmonic ITO nanotubes with controllable hyperbolic response are introduced. The synthesis is achieved by a template‐based liquid‐phase technique. The tuning mechanism is based on controlling the carrier density in ITO via oxygen vacancy concentration. The process is reversible, the photonic features are activated by creating oxygen vacancies and can be switched off by filling them up again. Further, it is shown that the carrier concentration can also be controlled via a static electric field. Optical simulations support the experimental findings and highlight the parameters that determine the optical response of the metamaterial. [ABSTRACT FROM AUTHOR]

Hybrid Perovskite materials have gone through an astonishing development due to their unique optoelectronic behavior, leading to the creation of a wide range of synthetic strategies. As the materials’ surface is found to play a crucial role with respect to the properties, e.g. hydration, stability and carrier mobilities, considerable efforts have been made to optimize the surface through various approaches. Especially the passivation of the perovskite surface attracted a lot of attention in this field, often resulting in more complex, multi‐step synthetic processes. In this study, a simple one‐step aerosol‐assisted synthetic approach is presented to obtain thiocyanate (SCN) passivated single‐crystal MAPbBr3 microcrystals. To elucidate the role of the additive in the crystallization process, mixed (pseudo‐)halide precursors are systematically investigated. The as processed, passivated microcrystals exhibit enhanced stability and charge carrier lifetimes. Additionally, a decrease in surface photovoltage, attributed to the presence of the SCN additive, is observed. Furthermore, the aerosol process is further developed resulting in a novel binary system containing MAPbBr3‐SCN perovskite microcrystals and Au nanostructures. This system serves as a promising model for further investigations into potential interactions between plasmonic and semiconducting materials, with initial results indicating prolonged charge carrier lifetimes. [ABSTRACT FROM AUTHOR]

The properties of porous materials benefit from hierarchical porosity. A less noted element of hierarchy is the occurrence of directionality in functional gradient materials. A sharp boundary is replaced by a transition from one feature to the next. The number of cases known for porous materials with either structural or chemical gradients is small. A method capable of generating combinations of structural and chemical gradients in one material does not exist. Such a method is presented with a focus on silver and nitrogen containing carbon materials because of the potential of this system for electrocatalytic CO2 reduction. A structural gradient results from controlled separation using ultracentrifugation of a binary mixture of template particles in a resorcinol–formaldehyde (RF) sol as carbon precursor. A new level of complexity can be reached, if the surfaces of the template particles are chemically modified. Although the template is removed during carbonization, the modification (Ag, N) becomes integrated into the material. Understanding how modified and unmodified large and small particles sediment in the RF sol enables almost infinite variability of combinations: chemically graded but structurally homogeneous materials and vice versa. Ultimately, a material containing one structural gradient and two chemical gradients with opposing directions is introduced. [ABSTRACT FROM AUTHOR]

Surfactants are functional molecules, which are used to stabilize interfaces of all kind, for example, in foams. They are produced in large amounts by the chemical industry and represent an inherent part of everyone′s daily routine. Next‐generation surfactants contain at least one additional feature, for example catalytic activity or special redox properties. Another class offers smart properties like thermoresponsivity. Ultimately, the surfactant′s head could reach a high degree of multifunctionality, "comparable" to a swiss army knife. For a comprehensive discussion see the Minireview by S. Polarz et al. on page 18842 ff. [ABSTRACT FROM AUTHOR]

Ruddlesden‐Popper‐type oxides exhibit remarkable chemical stability in comparison to perovskite oxides. However, they display lower oxygen permeability. We present an approach to overcome this trade‐off by leveraging the anisotropic properties of Nd2NiO4+δ. Its (a,b)‐plane, having oxygen diffusion coefficient and surface exchange coefficient several orders of magnitude higher than its c‐axis, can be aligned perpendicular to the gradient of oxygen partial pressure by a magnetic field (0.81 T). A stable and high oxygen flux of 1.40 mL min−1 cm−2 was achieved for at least 120 h at 1223 K by a textured asymmetric disk membrane with 1.0 mm thickness under the pure CO2 sweeping. Its excellent operational stability was also verified even at 1023 K in pure CO2. These findings highlight the significant enhancement in oxygen permeation membrane performance achievable by adjusting the grain orientation. Consequently, Nd2NiO4+δ emerges as a promising candidate for industrial applications in air separation, syngas production, and CO2 capture under harsh conditions. [ABSTRACT FROM AUTHOR]

Das natürliche Blatt ist ein Paradebeispiel für ein System, das kontinuierlich Wertschöpfung betreibt, indem es z. B. CO2 in Zucker umwandelt. Wichtigster Bestandteil sind die gekoppelten Photosysteme II und I, die in der Zellmembran eingebettet sind. Können ihre Schlüsselfunktionen auf ein Tensid übertragen werden? Wir stellen moderne Tenside vor, die sich zu zweischichtigen Vesikeln anordnen (ähnlich der Zellmembran), fähig sind, Photonen verschiedener Wellenlängen zu absorbieren und angeregte Ladungsträger auszutauschen (ähnlich zu Photosystem II und I), sowie CO2 umzuwandeln (analog zum Blatt). Die Tenside bestehen aus fünf Farbstoffeinheiten als hydrophobe Gruppe, allesamt auf einer Seite des polyhydroxylierten Fullerenols, das als Kopfgruppe dient (Janus‐artig). Wir berichten über tensidische, optische, elektronische und katalytische Eigenschaften, sowie davon, wie von den Farbstoffen absorbierte Photonen zur Fullerenol‐Kopfgruppe transportiert werden, wo sie z. B. mit CO2 reagieren und dieses zu Ameisensäure reduzieren können. [ABSTRACT FROM AUTHOR]

The leaf is a prime example of a material converting waste (CO2) into value with maximum sustainability. As the most important constituent, it contains the coupled photosystems II and I, which are imbedded in the cellular membrane of the chloroplasts. Can key functions of the leaf be packed into soap? We present next‐generation surfactants that self‐assemble into bilayer vesicles (similar to the cellular membrane), are able to absorb photons of two different visible wavelengths, and exchange excited charge carriers (similar to the photosystems), followed by conversion of CO2 (in analogy to the leaf). The amphiphiles contain five dye molecules as the hydrophobic entity attached exclusively to one hemisphere of a polyhydroxylated fullerene (Janus‐type). We herein report on their surfactant, optical, electronic, and catalytic properties. Photons absorbed by the dyes are transferred to the fullerenol head, where they can react with different species such as CO2 to give formic acid. [ABSTRACT FROM AUTHOR]

Learning which parameters influence order is important for the generation of future particle‐based materials. Aspect ratio and polydispersity could be influenced independently from each other for ZnO nanorods. Sebastian Polarz and co‐workers deduce the impact on order parameters and structural defects from a quantitative evaluation of electron microscopy data in article number 1600215. [ABSTRACT FROM AUTHOR]

Once the optical, electronic, or photocatalytic properties of a semiconductor are set by adjusting composition, crystal phase, and morphology, one cannot change them anymore, respectively, on demand. Materials enabling postsynthetic and reversible switching of features such as absorption coefficient, bandgap, or charge carrier dynamics are highly desired. Hybrid perovskites facilitate exceptional possibilities for progress in the field of smart semiconductors because active organic molecules become an integral constituent of the crystalline structure. This paper reports the integration of ferrocene ligands into semiconducting 2D phases based on lead bromide. The complex crystal structures of the resulting, novel ferrovskite (≃ ferrocene perovskite) phases are determined by 3D electron diffraction. The ferrocene ligands exhibit strong structure‐directing effects on the 2D hybrid phases, which is why the formation of exotic types of face‐ and edge‐sharing lead bromide octahedra is observed. The bandgap of the materials ranges from 3.06 up to 3.51 eV, depending on the connectivity of the octahedra. By deploying the redox features of ferrocene, one can create defect states or even a defect band leading to control over the direction of exciton migration and energy transport in the semiconductor, enabling fluorescence via indirect to direct gap transition. [ABSTRACT FROM AUTHOR]

Defects among the grains of MOF polycrystalline membranes lead to non-selective gas transport, thereby reducing their selectivity in gas separation. In this work, ZIF-62 polycrystalline membranes with a well-intergrown structure were prepared on MXene-modified supports. Subsequent thermal treatment transformed the membranes into glass membranes, effectively eliminating non-selective defects at grain boundaries. Due to the incorporation of the MXene film and the vertical positioning of the support during the solvothermal process, only a minimal portion of the glass melt infiltrated into the porous support. Across the temperature range of 303 K–423 K and pressure range of 1 bar–3 bar, the ZIF-62 glass membranes showcased superior helium separation property and long-term chemical stability (resistant to CO 2 and H 2 O). The helium permeance reached approximately 51 GPU, with selectivities against N 2 and CH 4 being 17.4 and 13.9, respectively, outperforming current MOF membranes. [Display omitted] • Zinc ions are absorbed and intercalated into a thin film of the 2D material MXene. • Well-intergrown ZIF-62 membranes are prepared on MXene modified Al 2 O 3 supports. • ZIF-62 polycrystalline membranes melt to glass membranes upon a thermal treatment. • The infiltration of the glass liquid into supports has been effectively prevented. • ZIF-62 glass membranes exhibit great helium separation performance. [ABSTRACT FROM AUTHOR]

Abstract: The main ability of amphiphilic molecules is to alter the energy of interfaces. They aid in the formation of various materials characterized by a high surface to volume ratio. Furthermore, amphiphiles tend to self-organize into structures of higher complexity. In the current study anionic surfactants containing a purely inorganic multinuclear head group of the polytungstate type R-[PW11O3O39]3- were synthesized. Alkyl chains of different length were attached to the head group via siloxy bridges. Furthermore, the counterions could be varied. Ultimately, a heteropolyacid surfactant (H+ as the counterion) could be prepared. The self-assembly behavior of the polyoxometalate surfactants into micelles and even lyotropic phases was studied. For instance, the formation of a phase with P6/mm symmetry containing hexagonally packed cylinders has been observed. Finally, it was possible to extend the functionality of classical amphiphiles. The polyoxometalate amphiphiles have been used for the emulsification of and, at the same time, as the initiator for the cationic polymerization of styrene. As a result, interesting organic-inorganic hybrid polymer latexes with surfaces containing heteropolyacid entities were prepared. [ABSTRACT FROM AUTHOR]

The article titled "Multiplying Oxygen Permeability of a Ruddlesden-Popper Oxide by Orientation Control via Magnets" discusses the magnetic anisotropy and oxygen transport anisotropy of the Ruddlesden-Popper oxide Nd2NiO4+δ. The study shows that by aligning the (a,b)-plane of the oxide perpendicular to the gradient of oxygen partial pressure using a magnetic field generated by permanent magnets, the oxygen flux of the membrane can be increased five times compared to a randomly oriented membrane. The research, conducted by Zhijun Zhao, Armin Feldhoff, and their colleagues, provides valuable insights into enhancing the oxygen permeability of oxide membranes. [Extracted from the article]

The article titled "Multiplying Oxygen Permeability of a Ruddlesden–Popper Oxide by Orientation Control via Magnets" discusses the magnetic anisotropy and oxygen transport anisotropy of the Ruddlesden–Popper oxide Nd2NiO4+δ. The study found that by aligning the (a,b)-plane of the oxide perpendicular to the gradient of oxygen partial pressure using a magnetic field generated by permanent magnets, the oxygen flux of the membrane can be increased five times compared to a randomly oriented membrane. This research was conducted by Zhijun Zhao, Armin Feldhoff, and their colleagues. [Extracted from the article]

The central promise of nanoparticle‐based materials is that cooperative properties may emerge, when individual quantum dots are positioned on a periodic lattice. Yet, there are only a few papers in the literature reporting such effects. Nevertheless, it is clear that the symmetry of the superlattice is decisive for the desired emergent phenomena. An interesting question is, how the symmetry of the initial monodisperse nanoparticles affects the structure of the colloidal crystal during self‐assembly processes. For instance, particles with a hexagonal cross‐section demonstrate self‐organization, which is very similar to spherical colloids. Likewise, one would also expect that trigonal nanoparticles behave similarly. Unfortunately, it is very hard to obtain monodisperse semiconductor colloids with a trigonal shape, because this requires a symmetry break during morphogenesis of the nanocrystal. While such a symmetry break is known in the literature for structures attached to a solid substrate, herein, colloidal synthesis of trigonal ZnO nanorods is successfully demonstrated, and the mechanism is elucidated via experimental and theoretical methods. 2D‐superlattices formed by such particles with trigonal cross‐section are compared to hexagonal analogues. It is found that there are distinct differences, which result in important differences in properties such as the formation of voids and also in optical properties. [ABSTRACT FROM AUTHOR]

Amphiphiles alter the energy of surfaces, but the extent of this feature is typically constant. Smart systems with amphiphilicity as a function of an external, physical trigger are desirable. As a trigger, the exposure to a magnetic field, in particular, is attractive because it is not shielded in water. Amphiphiles like surfactants are well known, but the magnetic response of molecules is typically weak. Vice‐versa, magnetic particles with strong response to magnetic triggers are fully established in nanoscience, but they are not amphiphilic. In this work colloids with Janus architecture and ultra‐small dimensions (25 nm) have been prepared by spatial control over the thiol‐yne click modification of organosilica‐magnetite core–shell nanoparticles. The amphiphilic properties of these anisotropically modified particles are proven. Finally, a pronounced and reversible change in interfacial stabilization results from the application of a weak (<1 T) magnetic field. [ABSTRACT FROM AUTHOR]

A paradigm for active constituents in (homogeneous) catalysis is that optimum performance requires maximum dispersion. Generally, aggregation results in a decline. This is a different case in supramolecular catalysis. A new concept based on surfactants equipped with functional heads is presented, which becomes a more active catalyst itself upon aggregation. The head group of the surfactants is composed of a diethylenetriamine‐functionalized fullerene capable of coordinating to catalytically active metals like CoII. The improvement of catalytic properties upon aggregation is demonstrated via electrocatalytic water‐splitting reaction as a model system. Detailed electrochemistry studies were performed at concentrations below and above the critical aggregation concentration (cac). While isolated surfactant molecules represent only moderately active catalysts, drastic improvement of efficiency in the hydrogen evolution (HER) as well as in the oxygen evolution reactions (OER) were detected, once vesicular structures have formed. Self‐organization of the surfactants leads to an increase in turnover frequencies of up to 1300 % (HER). The strongly beneficial effect of aggregation arises from the favorable alignment of individual molecules, thus, facilitating intermolecular charge transfer processes in the vesicles. [ABSTRACT FROM AUTHOR]

Particle-based materials are expected to exhibit cooperative effects, if nanoparticles form periodic arrays. For particle shapes deviating from a spherical morphology, it is difficult to obtain monodisperse samples. Therefore, we investigated the influence of polydispersity of anisotropic nanoparticles in 2D colloidal crystallization. We work with hexagonal ZnO nanoplates with sizes below 50 nm, and tuned the directionality of the inter-particle interaction by choice of capping agents. Surprisingly, there was no glass to crystal transition for a critical polydispersity value, but a continuous transition. [ABSTRACT FROM AUTHOR]

Rutile TiO 2 nanorod arrays (NRAs) are applicable in various prospective technologies. Hydrothermal methods present a simple technique to fabricate such NRAs. In this report, we present the fabrication of seed layers for the hydrothermal growth of rutile TiO 2 nanorods via sputter deposition, electron-beam evaporation, and sol-gel method and study the influence of each on the growth behavior. To satisfy the requirements of numerous applications, p-type silicon, platinum, levitating carbon membranes, a template made of polystyrene spheres, and commercial fluorine tin oxide (FTO) were employed as substrates. We document the structural properties of the TiO 2 seed layers and describe the relationship between the characteristics of the seed crystals, the growth evolution, and the appearance of as-grown nanorods. Various growth stages of rutile TiO 2 nanorods are compared depending on whether they are grown on polycrystalline TiO 2 or FTO seed layers. In both cases, a homogenous TiO 2 bottom layer is formed at the seed layer/substrate interface, which is essential for electronic applications such as hybrid solar cells. Detached NRAs illustrate the effect of rutile FTO and TiO 2 on the porosity of this bottom layer. Further details about the formation process of this layer are obtained from the growth on confined seed layers fabricated by electron-beam lithography. [ABSTRACT FROM AUTHOR]

Processing of substrates with different solvent compatibility is a persistent problem in homogeneous catalysis, in particular when one starting compound is water soluble and the other is not. A promising concept reported in the literature is micellar catalysis. However, the process of developing catalysts that are surfactants at the same time is still in its early stages. We report the synthesis of a new surfactant system with an N-heterocyclic carbene (NHC) moiety as a head group. Characteristic surfactant properties such as the formation of micelles or liquid crystals is documented. The new surfactant ligand forms coordination compounds with various metals, most importantly Pd2+, in square planar geometry. In addition, the Pd-NHC compound shows surfactant features, and can be used successfully for C−C cross-coupling reactions (Suzuki, Heck). The boost in catalytic activity by one order of magnitude compared to analogous but non-amphiphilic species is reported. [ABSTRACT FROM AUTHOR]

Separation of compounds using liquid chromatography is a process of enormous technological importance. This is true in particular for chiral substances, when one enantiomer has the desired set of properties and the other one may be harmful. The degree of development in liquid chromatography is extremely high, but still there is a lack in understanding based on experimental data how selectivity works on a molecular level directly at the surfaces of a porous host material. We have prepared amino-acid containing organosilica as such host materials. Watching the rotational dynamics of chiral spin probes using electron paramagnetic resonance spectroscopy allows us to differentiate between surface adsorbed and free guest species. Diastereotopic selectivity factors were determined, and the influence of chiral surface group density, chemical character of the surface groups, pore-size, and temperature was investigated. We found higher selectivity values in macroporous solids with a rather rigid organosilica network and at lower temperature, indicating the significant effect of confinement effects. In mesoporous materials features are opposed with regards to the T-dependent behavior. From EPR imaging techniques and the resulting (macroscopic) diffusion coefficients, we could confirm that the correlations found on the microscopic level transform also to the macroscopic behavior. Thus, our study is of value for the development of future chromatography materials by design. [ABSTRACT FROM AUTHOR]

Diffusion in porous materials is under ongoing active investigation due to its major role in practical applications such as catalysis and chromatography. The complexity of these systems limits the use of the Einstein-Stokes diffusion theory, and it must be distinguished between the microscopic scale of diffusion at a molecular level, which is sensitive to the local surroundings of a diffusing molecule, and the macroscopic scale which takes into account diffusion spanning multiple pores, grain boundaries and inhomogeneity within the material. Here, we employ an in situ approach for quantitative measurements of the diffusion on a macroscopic length scale. For the first time, full time-resolved spectral spatial EPR imaging in combination with the simultaneous iterative reconstruction technique (SIRT) allows the simultaneous observation of the diffusion of two different molecular species inside of an aerogel in a single experiment. [ABSTRACT FROM AUTHOR]

Gaining external control over self-organization is of vital importance for future smart materials. Surfactants are extremely valuable for the synthesis of diverse nanomaterials. Their self-assembly is dictated by microphase separation, the hydrophobic effect, and head-group repulsion. It is desirable to supplement surfactants with an added mode of long-range and directional interaction. Magnetic forces are ideal, as they are not shielded in water. We report on surfactants with heads containing tightly bound transition-metal centers. The magnetic moment of the head was varied systematically while keeping shape and charge constant. Changes in the magnetic moment of the head led to notable differences in surface tension, aggregate size, and contact angle, which could also be altered by an external magnetic field. The most astonishing result was that the use of magnetic surfactants as structure-directing agents enabled the formation of porous solids with 12-fold rotational symmetry. [ABSTRACT FROM AUTHOR]

Nonequilibrium states of matter are arousing huge interest because of the outstanding possibilities to generate unprecedented structures with novel properties. Self-organizing soft matter is the ideal object of study as it unifies periodic order and high dynamics. Compared to settled systems, it becomes vital to realize more complex interaction patterns. A promising and intricate approach is implementing controlled balance between attractive and repulsive forces. We try to answer a fundamental question in surfactant science: How are processes like lyotropic liquid crystals and micellization affected, when headgroup charge becomes so large that repulsive interactions are inevitable? A particular challenge is that size and shape of the surfactant must not change. We could realize the latter by means of new hybrid surfactants with a heteropolyanion head [EW11O39]n− (E = PV, SiIV, BIII; n = 3, 4, 5). Among the unusual self-assembled structures, we report a new type of micelle with dumbbell morphology. [ABSTRACT FROM AUTHOR]

In this work, we describe the role of the different layers in perovskite solar cells to achieve reproducible, ~16% efficient perovskite solar cells. We used a planar device architecture with PEDOT:PSS on the bottom, followed by the perovskite layer and an evaporated C60 layer before deposition of the top electrode. No high temperature annealing step is needed, which also allows processing on flexible plastic substrates. Only the optimization of all of these layers leads to highly efficient and reproducible results. In this work, we describe the effects of different processing conditions, especially the influence of the C60 top layer on the device performance. [ABSTRACT FROM AUTHOR]

The conversion of waste into valuable products is most appealing in the case of CO 2 , a molecule which is produced in mass by our society and industries. Because its atmospheric concentration correlates to climate change and the green-house effect, major efforts are on the way to reduce the emission of CO 2. One promising strategy is the separation of CO 2 from the gas-phase (e.g. flue gases) by solid-adsorbents containing amine moieties. The synthesis of tailor-made adsorbents with changing surface properties remains a challenge. This work presents a click chemistry approach that enables the easy modification of organosilica materials with functional groups that can be used as model systems to study the influence of surface chemistry on CO 2 adsorption. As an example, the modification of the materials with primary amines is discussed in detail but furthermore the approach offers the possibility to tailor the surface properties using any desired functional group. The increased affinity of the used copper catalyst introduced some difficulties but we were able to remove all remains of copper. With this approach, we were able to synthesize materials with different degrees of functionalization up to 80%. This approach for the development of new carbon capture model systems offers high functionalization combined with the flexibility of a post-functionalization approach. Thus, surface chemistry can be tailored to study the influence of surface chemistry on CO 2 adsorption. As an example for the model character of our materials, we could show that the heat of adsorption can be tuned by systematically varying the degree of amine functionalization. Image 1 • Versatile click chemistry approach with degrees of functionalization up to 80%. • Offers opportunity to generate vertical and radial gradients in functionalization. • Isosteric heat of adsorption can be varied systematically with amine concentration. • Approach enables generation of materials with gradients in heat of adsorption. [ABSTRACT FROM AUTHOR]

Unlike conventional colloids showing random mobility because of Brownian motion, active colloids contain nanomotors that translate chemical or physical triggers into directed movement. Whereas the acceleration of such particles works well, it is difficult to decelerate them by request. Compared to the existing literature on microscaled swimmers/robots, the main question of the current paper is whether nanoscaled colloids (<100 nm) can also be actively controlled despite the stronger relevance of rotational diffusion at such dimensions. We developed nanoparticles comprising two independent mechanisms for propulsion: a chemical engine associated with a Janus-type modification of organosilica nanoparticles and physical locomotion because of a superparamagnetic core inside these particles. Both triggers can be used independently to initiate the particles' directed and anisotropic movement. The magnetic forces can be tuned, most importantly concerning the angle defining the chemical acceleration. Superposition and a boost state are adopted for a parallel alignment. However, when the magnetic field acting on the particles is turned to an antiparallel orientation, a rapid deceleration can be observed, and the colloids halt.

Using colloidal particles as models to understand processes on a smaller scale is a precious approach. Compared to molecules, particles are less defined, but their architecture can be more complex and so is their long-range interaction. One can observe phenomena that are unknown or much more difficult to realize on the molecular level. The current paper focuses on particle-based surfactants and reports on numerous unexpected properties. The main goal is creating an amphiphilic system with responsiveness in surface activity and associated self-organization phenomena depending on applying an external trigger, preferably a physical field. A key step is the creation of a Janus-type particle characterized by two types of dipoles (electric and magnetic) which geometrically stand orthogonal to each other. In a field, one can control which contribution and direction dominate the interparticle interactions. As a result, one can drastically change the system's properties. The features of ferrite-core organosilica-shell particles with grain-like morphology modified by click chemistry are studied in response to spatially isotropic and anisotropic triggers. A highly unusual aggregation-dissolution-reaggregation sequence w as discovered. Using a magnetic field, one can even switch off the amphiphilic properties and use this for the field-triggered breaking of multiphase systems such as emulsions., (© 2023 The Authors. Small published by Wiley-VCH GmbH.)

Oxidative stress is a cause for numerous diseases and aging processes. Thus, researchers are keen to tune the level of intracellular stress and to learn from that. An unusual approach is presented here. The methodology involves multifunctional surfactants. Although their molecular design is nonbiological-a fullerenol head group attached covalently to pi-conjugated dyes-the surfactants possess superior biocompatibility. Using an intrinsic fluorescence signal as a probe, it is shown that the amphiphiles become incorporated into the Caco-2 cells. There, they are able to exhibit additional functions. The compound reduces cellular stress in dark reaction pathways. The antagonistic property is activated under irradiation, the photocatalytic production of reactive oxygen species (ROS), resulting in cell damage. The feature is activated even by near-infrared light (NIR-light) via a two-photon process. The properties as molecular semiconductors lead to a trojan horse situation and allows the programming of the spatial distribution of cytotoxicity., (© 2023 The Authors. Advanced Healthcare Materials published by Wiley-VCH GmbH.)

Many pathogenic bacteria are getting more and more resistant against antibiotic treatment and even become up to 1.000× times more resilient in the form of a mature biofilm. Thus, one is currently prospecting for alternative methods for treating microbial infections, and photodynamic therapy is a highly promising approach by creating so-called reactive oxygen species (ROS) produced by a photosensitizer (PS) upon irradiation with light. Unfortunately, the unspecific activity of ROS is also problematic as they are harmful to healthy tissue as well. Notably, one knows that uncontrolled existence of ROS in the body plays a major role in the development of cancer. These arguments create need for advanced theranostic materials which are capable of autonomous targeting and detecting the existence of a biofilm, followed by specific activation to combat the infection. The focus of this contribution is on mesoporous organosilica colloids functionalized by orthogonal and localized click-chemistry methods. The external zone of the particles is modified by a dye of the Hoechst family. The particles readily enter a mature biofilm where adduct formation with extracellular DNA and a resulting change in the fluorescence signal occurs, but they cannot cross cellular membranes such as in healthy tissue. A different dye suitable for photochemical ROS generation, Acridine Orange, is covalently linked to the surfaces of the internal mesopores. The spectral overlap between the emission of Hoechst with the absorption band of Acridine Orange facilitates energy transfer by Förster resonance with up to 88% efficiency. The theranostic properties of the materials including viability studies were investigated in vitro on mature biofilms formed by Pseudomonas fluorescens and prove the high efficacy.

The capability of ordinary surfactants in solubilizing hydrophobic compounds can come to a limit, if the extension of a contaminant is too large. An attractive goal is the development of surfactants which can actively reduce the size of dirt. Because strong Lewis acids are known to catalyze both bond formation and cleavage, an integration into the surfactant's molecular framework is tempting. End-group functionalized hepta-dentate ligands, which coordinate to metal ions preventing deactivation by hydrolysis over a broad range of pH values while maintaining strong Lewis-acidity, are herein presented. After proof of amphiphilicity and surfactant characteristics, catalytic properties are investigated for different reactions including the cleavage of proteins. The compounds perform better than benchmark catalysts concerning the attack of unreactive amide bonds. A study with two Sc 3+ species as the active site, one non-amphiphilic, the other one being surface-active, underlines the positive effect of surfactant properties for boosting catalytic efficiency.

Improved carbon capture materials are crucial for managing the CO 2 level in the atmosphere. The past focus was on increasing adsorption capacities. It is widely known that controlling the heat of adsorption (ΔH ads ) is equally important. If it is too low, CO 2 uptake takes place at unfavorable conditions and with insufficient selectivity. If it is too high, chemisorption occurs, and the materials can hardly be regenerated. The conventional approach for influencing ΔH ads is the modification of the adsorbing center. This paper proposes an alternative strategy. The hypothesis is that fine-tuning of the molecular environment around the adsorbing center is a powerful tool for the adjustment of CO 2 -binding properties. Via click chemistry, any desired neighboring group (NG) can be incorporated on the surfaces of the nanoporous organosilica model materials. Passive NGs induce a change in the polarity of the surface, whereas active NGs are capable of direct interaction with the active center/CO 2 pair. The effects on ΔH ads and on the selectivity are studied. A situation can be realized which resembles frustrated Lewis acid-base pairs, and the investigation of the binding-species by solid-state NMR indicates that the push-pull effects could play an essential role not only in CO 2 adsorption but also in its activation., (© 2021 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Metallosurfactants are molecular compounds which combine the unique features of amphiphiles, like their capability of self-organization, with the peculiar properties of metal complexes like magnetism and a rich redox chemistry. Considering the high relevance of surfactants in industry and science, amphiphiles that change their properties on applying an external trigger are highly desirable. A special feature of the surfactant reported here, 1-( Z )-heptenyl-1'-dimethylammonium-methyl-(3-sulfopropyl)ferrocene ( 6 ), is that the redox-active ferrocene constituent is in a gemini-position. Oxidation to 6+ induces a drastic change of the surfactant's properties accompanied by the emergence of paramagnetism. The effects of an external magnetic field on vesicles formed by 6+ and the associated dynamics were monitored in situ using a custom-made optical birefringence and dual dynamic light scattering setup. This allowed us to observe the optical anisotropy as well as the anisotropy of the diffusion coefficient and revealed the field-induced formation of oriented string-of-pearls-like aggregates and their delayed disappearance after the field is switched off., Competing Interests: The authors declare no competing financial interests., (This journal is © The Royal Society of Chemistry.)

For every mass product, there are problems associated with the resulting waste. Residues of hormones in urine cannot be removed sufficiently from wastewater, and this has undesired consequences. An ideal adsorbent would take up the impurity, enable a simple separation and recyclability. Polymer colloids with high affinity towards the drug, accessible porosity, high surface area, and stimuli-responsive properties would be candidates, but such a complex system does not exist. Here, porous vinyl-functionalized organosilica nanoparticles prepared from a styrene bridged sol-gel precursor act as monomers. Initiation of the polymerization at the pore walls and addition of functional monomers result in a special copolymer, which is covalently linked to the surface and covers it. An orthogonal modification of external surface was done by click attachment of a thermoresponsive polymer. The final core-shell system is able to remove quantitatively hydrophobic molecules such as the hormone progesterone from water. A change of temperature closes the pores and induces the aggregation of the particles. After separation one can reopen the particles and recycle them., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Resistive switching devices offer a great potential for advanced computing and data storage, including neuromorphic networks and random-access memory. State-of-the-art memristors are mostly realized by a three-layer structure, which is comprised of an active metal oxide layer sandwiched between two metal electrodes. Thus, there is always an interface involving two materials differing strongly in crystallographic and electronic properties. In this study, we present a resistive switching nanorod device based on a metal oxide sandwiched between two transparent conductive oxide electrodes. Thus, the system is characterized by a different, smooth interface offering new possibilities for increased energy efficiency and transparent electronics. Antimony-doped tin oxide (ATO) is used as an electrode material. The heavily doped ATO nanorods, exhibiting a good conductivity, are produced by a templated electrochemical deposition approach of alloy particles with subsequent thermal oxidation. The process enables precise control of the doping level within the nanorods and the formation of a doping level gradient. Electrical characterization reveals that a stronger gradient between heavily doped and undoped tin oxide within the nanorods results in a more rectifying character of the junction. Three-domain nanorods consisting of an undoped tin oxide segment in between two ATO segments are utilized to introduce memristive properties into the nanorod device. The resistive switching of these nanorods can be attributed to an oxygen vacancy doping gradient introduced during thermal oxidation. These vacancies are mobile within the tin oxide host structure and their injection from the ATO segment into the undoped tin oxide segment results in altered conductivity of the device, when an external bias is applied.

Cells exist in the so-called extracellular matrix (ECM) in their native state, and numerous future applications require reliable and potent ECM-mimics. A perspective, which goes beyond ECM emulation, is the design of a host-material with features which are not accessible in the biological portfolio. Such a feature would, for instance, be the creation of a structural or chemical gradient, and to explore how this special property influences the biological processes. First, we wanted to test if macroporous organosilica materials with appropriate surface modification can act as a host for the implementation of human cells like HeLa or LUHMES. It was possible to use a commercially available polymeric foam as a scaffold and coat it with a thiophenol-containing organosilica layer, followed by biofunctionalization with biotin using click chemistry and the subsequent coupling of streptavidin-fibronectin to it. More importantly, deformation of the scaffold allowed the generation of a permanent structural gradient. In this work, we show that the structural gradient has a tremendous influence on the capability of the described material for the accommodation of living cells. The introduction of a bi-directional gradient enabled the establishment of a cellular community comprising different cell types in spatially distinct regions of the material. An interesting perspective is to study communication between cell types or to create cellular communities, which can never exist in a natural environment., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In the vast majority of studies on semiconductor particles ligands or capping agents are used that bind to the surface of the particles covering them with an electrically insulating shell. Since the transport of charge carriers and/or energy across interfaces is desirable for a variety of applications, the use of π-conjugated ligands becomes increasingly interesting. Among them are compounds that react to external stimuli. Molecular switches in particular are fascinating because the properties of the interfaces can be potentially adjusted as required. However, there is debate about how the properties of such special ligands are influenced by the presence of a semiconductor and vice versa. Here ammonium-modified azobenzene compounds were selected as prototypes for molecular switches and organic-inorganic hybrid perovskites as semiconductor materials. The class of ammonium-lead-halide phases as prototypes is peculiar because, in addition to the surface functionalization of 3D crystals, organic compounds can actually be incorporated into the crystal as 2D phases. Thus, for example, layered Ruddlesden-Popper phases are obtained. We present photoswitchable azobenzene ligands with different head-group lengths for the synthesis of 2D and 3D hybrid perovskite phases. The energy transfer mechanisms are influenced by the length of the molecular spacer moiety, which determines the distance between the π system and the semiconductor surfaces. We find huge differences in the photoswitching behaviour between the free, surface-coordinated and integrated ligands between the perovskite layers. Photoswitching of azobenzene ligands incorporated in 2D phases is nearly quenched, while the same mechanism for surface-coordinating ligands is greatly improved, compared to the free ligands. The improvement originates from an energy transfer from perovskite to azobenzene, which is strongly distance-dependent. This study provides evidence for the photoswitching of azobenzenes as ligands of hybrid perovskites, which depends on the spacing between the chromophore and the perovskite phase., (Copyright © 2020, Fillafer et al.; licensee Beilstein-Institut.)

Next-generation surfactants provide extended functionality apart from their amphiphilic properties. We present two novel metallosurfactants characterized by an N-heterocyclic carbene (NHC) head bearing Cu(I) and Fe(II). An innovative approach for their application in emulsion polymerizations under atom transfer radical polymerization (ATRP) conditions was developed. Thereby the complexes fulfilled the role of emulsifiers, active catalysts, and stabilization agents at once. Polymerization of methyl methacrylate (MMA) yielded stable poly(methyl methacrylate) (PMMA) colloids in water with the catalyst located at the surface of the colloids. The termination of PMMA with a bromine moiety enabled the subsequent copolymerization with styrene via macroinitiation and PMMA-polystyrene (PS) core-shell particles were obtained. Gel permeation chromatography (GPC) and selective gradient NMR experiments revealed a covalent linkage between the PMMA core and the PS shell.

The maximization of activity is a general aim in catalysis research. The possibility for light-triggered enhancement of a catalytic process, even if the process is not photochemical in nature, represents an intriguing concept. Here, we present a novel system for the exploration of the latter idea. A surfactant with a catalytically active head group, a protonated polyoxometalate (POM) cluster, is attached to the surface of a gold nanoparticle (Au NP) using thiol coupling chemistry. The distance of the catalytically active center to the gold surface could be adjusted precisely using surfactants containing hydrocarbon chains (C n ) of different lengths ( n = 4-10). Radiation with VIS-light has no effect on the catalytic activity of micellar aggregates of the surfactant. The situation changes, as soon as the surfactants have been attached to the Au NPs. The catalytic activity could almost be doubled. It was proven that the effect is caused by coupling the surface plasmon resonance of the Au NPs with the properties of the POM head group. The improvement of activity could only be observed if the excitation wavelength matches the absorption band of the used Au NPs. Furthermore, the shorter the distance between the POM group and the surface of the NP, the stronger is the effect. This phenomenon was explained by lowering the activation energy of the transition state relevant to the catalytic process by the strong electric fields in the vicinity of the surfaces of plasmonic nanoparticles. Because the catalytic enhancement is wavelength-selective, one can imagine the creation of complex systems in the future, a system of differently sized NPs, each responsible for a different catalytic step and activated by light of different colors.