The tuning of the optical properties of pyrene, immobilized on alumina nanoparticle surfaces, is demonstrated. To this end, phosphonic acid functionalized pyrene derivatives are shown to self‐assemble into stoichiometrically mixed monolayers featuring hydrophilic, hydrophobic, or fluorophilic phosphonic acid ligands and to form defined core–shell hybrids depending on the molecular mixing ratio and the nature of the ligand monomer, excimer, or mutual emission of both evolved. The spectroscopic observations are explained by the respective mobility of the dye molecules with respect to their fixed, specific anchor points and the resulting probability to form excimers and are supported by molecular dynamic simulations, X‐ray reflectivity measurements, and temperature‐dependent steady‐state fluorescence assays. In terms of an additional tuning of the emission color change and/or the on‐off switching of the fluorescence, the formation of core–shell–shell system is carried out by applying amphiphiles. The general concept is fully transferable to demobilized films of nanoparticles, thereby enabling a switchable solid‐state surface.

We describe a universal wet‐chemical shell‐by‐shell coating procedure resulting in colloidal titanium dioxide (TiO2) and iron oxide (Fe3O4) nanoparticles with dynamically and reversibly tunable surface energies. A strong covalent surface functionalization is accomplished by using long‐chained alkyl‐, triethylenglycol‐, and perfluoroalkylphosphonic acids, yielding highly stabilized core–shell nanoparticles with hydrophobic, hydrophilic, or superhydrophobic/fluorophilic surface characteristics. This covalent functionalization sequence is extended towards a second noncovalent attachment of tailor‐made nonionic amphiphilic molecules to the pristine coated core–shell nanoparticles via solvophobic (i.e. either hydrophobic, lipophobic, or fluorophobic) interactions. Thereby, orthogonal tuning of the surface energies of nanoparticles via noncovalent interactions is accomplished. As a result, this versatile bilayer coating process enables reversible control over the colloidal stability of the metal oxide nanoparticles in fluorocarbons, hydrocarbons, and water.

Au−Fe 3 O 4 nanoheterodimers were obtained by thermally decomposing iron oleate on presynthesized gold nanoparticles. Water solubility as well as surface charges were achieved by encapsulating the initially hydrophobic Au−Fe 3 O 4 nanoheterodimers in a self-assembled bilayer shell formed either by 1octadecylpyridinium, providing positive surface charges, or by 4-dodecylbenzenesulfonate, yielding a negatively charged surface. The surface charge and surface architecture were shown to control both the cellular entry and the intracellular trafficking of the Au−Fe 3 O 4 nanoheterodimers. The positively charged (1octylpyridinium-terminated) Au−Fe 3 O 4 nanoheterodimers were internalized by both breast cancer cells (MCF-7) and epithelial cells (MCF-10 A), wherein they were electrostatically bound at the negatively charged membranes of the cell organelles and, in particular, adsorbed onto the mitochondrial membrane. The treatment of MCF-7 and MCF-10 cells with a fractional X-radiation dose of 1 Gy resulted into a large increase of superoxide production, which arose from the Au− Fe 3 O 4 nanoheterodimer-induced mitochondrial depolarization. In contrast, the negatively charged (4-dodecylbenzenesulfonateterminated) Au−Fe 3 O 4 nanoheterodimers preferentially invaded the cancerous MCF-7 cells by direct permeation. X-ray treatment of MCF-7 cells, loaded with anionic Au−Fe 3 O 4 nanoheterodimers, yielded the increase of both hydroxyl radical and cytoplasmic superoxide formation. The X-radiation-induced activation of the Fe 3 O 4 surfaces, consisting of Fe 2+ and Fe 3+ cations, triggered the catalysis of the hydroxyl radical production, whereas superoxide formation presumably occurred through X-rayinduced photoelectron emission near the Au surface. Since hydroxyl radicals are highly cytotoxic and the negatively charged Au−Fe 3 O 4 NHDs spare the healthy MCF-10A cells, these Au−Fe 3 O 4 nanoheterodimers exhibit a higher potential for radiation therapy than the positively charged Au−Fe 3 O 4 nanoheterodimers. Encouraging results from the clonogenic cell survival assay and DMF calculations corroborate the excellent performance of the anionic Au−Fe 3 O 4 nanoheterodimers as an X-ray dosage enhancer.

A first series of examples for confined space interactions of electron‐rich and electron‐poor molecules organized in an internal corona of shell‐by‐shell (SbS)‐structured Al2O3 nanoparticle (NP) hybrids is reported. The assembly concept of the corresponding hierarchical architectures relies on both covalent grafting of phosphonic acids on the NPs surface (SAMs formation; SAM=self‐assembled monolayer) and exohedral interdigitation of orthogonal amphiphiles as the second ligand layer driven by solvophobic interactions. The electronic communication between the chromophores of different electron demand, such as pyrenes, perylenediimides (PDIs; with and without pyridinium bromide headgroups) and fullerenes was promoted at the layer interface. In this work, it is demonstrated that the efficient construction principle of the bilayer hybrids assembled around the electronically “innocent” Al2O3 core is robust enough to achieve control over electronic communication between electron‐donors and ‐acceptors in the interlayer region. The electronic interactions between the electron‐accepting and electron‐donating moieties approaching each other at the layer interface were monitored by fluorescence measurements.

photocatalysis is of great potential for targeted applications.Due to their unique chemical, electrical, magnetic, mechanical, and optical properties and their catalytic activity, zinc oxide (ZnO) and especially ZnO nanoparticles have received considerable attention in both application fields, solar energy conversion, and catalysis. ZnO is an n-type semiconductor with a wide energy band (3.37 eV) and a high bond energy (60 meV). [1,2] It offers a wide range of properties depending on morphology, size, orientation, and density of the crystals. [3] A good electron mobility, a large volume to surface area ratio, a high UV absorption, and a long life-span are advantageous when used as a photocatalyst in UV-light. [4] The catalytic activity in different model reactions has been examined in dependence on morphology, size and shape, and pH. [3,[5][6][7] As the ZnO properties depend on the structure, numerous nanoparticle synthesis routes have been developed to create different shapes of ZnO structures such as 1D, 2D, and 3D structures including nanorods, nanoneedles, and nanoflowers. [8][9][10][11] A powerful technique to control the morphology is the use of surface-modifying substances, in particular macromole cules. [1] A number of studies have investigated various polymers such as polymethacrylic acid, polyethylene oxide (PEO) and PEO containing copolymers. [11][12][13][14][15] The application of polyethylene oxide-block-polymethacrylic acid (PEO-b-PMAA) copolymers as surface modifiers for ZnO has been thoroughly examined. [16] The photocatalytic activity and selectivity of novel binary and ternary composite nanostructures from polyethylene oxide-stabilized zinc oxide (PEO-ZnO) with and without polyoxometalate (H 4 [Si(W 3 O 10 ) 4 ], POM) are determined in aqueous solution under UV-light. Mono-and di-COOH-end-functionalized PEO polymers are used as surface modifiers, influencing the morphology and stability of the ZnO nanoparticles being synthesized in water. POM acts as an additional versatile photocatalytically active building block resulting in a ternary hybrid structure with tunable photocatalytic activity. Catalytic selectivity is demonstrated by studying photocatalytic dye degradations as model reactions, where the chemical backbone of the dyes and their charge turn out to be the basis for the selectivity. All samples are characterized with dynamic light scattering, transmission electron microscopy, scanning electron microscopy, light microscopy, and ζ-potential measurements. With the functionalized PEOs, large ZnO clusters consisting of leaves are formed while 2-[2-(2-methoxyethoxy) ethoxy] acetic acid (TODA) yields ZnO flower-like structures.