No abstract

A modular construction kit with two orthogonal noncovalent binding sites for self-assembly of supramolecular architectures is presented. The heteroditopic building blocks contain a terpyridine (tpy) unit for coordination of metal ions and a Hamilton receptor for multiple H-bonding of cyanuric acid derivatives. The association constants of ligand binding of M(II) complexes (M=Ru, Zn, Fe, and Pt) with a dendritic end cap were determined to be in the range of 10(2) and 10(4) L mol(-1) in chloroform. The capabilities for binding of metal ions were investigated by (1)H NMR and UV/Vis spectroscopy. The Fe complexes are most appropriate for the generation of discrete and high-ordered architectures due to their strong tendency to form FeL(2) complexes. Superstructures are readily formed in a one-pot procedure at room temperature. No mutual interactions between the orthogonal binding motifs were observed, and this demonstrates the highly specific nature of each binding process. Decomplexation experiments were carried out to examine the reversibility of Fe-tpy coordination. Substitution of the terminal end cap with a homoditopic bis-cyanurate linkage leads to formation of an iron-containing supramolecular strand. Formation of coordination polymers was confirmed by viscosity measurements. The supramolecular polymer strands can be reversibly cleaved by addition of a terminating cyanuric acid building block, and this proves the dynamic nature of this noncovalent polymerization process.

We present a fundamental study on ZnO nanorod–porphyrin assembly formation in solution, providing the key to novel tunable hybrid assemblies with potential in solar energy conversion.

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.