Matthias Georg Schwab

Catalyst-free preparation of melamine-based microporous polymer networks through Schiff base chemistry.

Recently, the synthesis of organic materials with high porosity has received considerable scientific interest, and various chemical approaches have been applied to the build-up of microporous polymer networks. In a novel catalyst-free process using Schiff base chemistry, melamine has been reacted with various di- and trivalent aldehydes to form a series of highly cross-linked microporous aminal networks with BET surface areas as high as 1377 m(2)/g and a NLDFT micropore volume of up to 0.41 cm(3)/g. It was shown that through the proper choice of the starting compounds the porosity of the final material can be fine-tuned. The materials contain up to 40 wt % of nitrogen and were also found to exhibit high thermal stability. Owing to the cheap and abundant monomers used in this study these networks are promising candidates for large-scale applications in gas storage, gas separation, catalysis, and sensing.

Direct access to metal or metal oxide nanocrystals integrated with one-dimensional nanoporous carbons for electrochemical energy storage.

Metal and metal oxide nanocrystals have sparked great interest due to their excellent catalytic, magnetic, and electronic properties. Particularly, the integration of metallic nanocrystals and one-dimensional (1D) electronically conducting carbons to form metal-carbon hybrids can lead to enhanced physical and chemical properties or even the creation of new properties with respect to single component materials. However, direct access to thermally stable and structurally ordered 1D metal-carbon hybrids remains a primary challenge. We report an in situ fabrication of Co(3)O(4) or Pt nanocrystals incorporated into 1D nanoporous carbons (NPCs) via an organometallic precursor-controlled thermolysis approach. The AB(2)-type (one diene and two dienophile) 3,4-bis(4-dodecynylphenyl)-substituted cyclopentadienone and its relevant cobalt or platinum complex are first impregnated into the nanochannels of AAO (anodic alumina oxide) membranes. The intermolecular Diels-Alder reaction of these precursor molecules affords the formation of cobalt or platinum functionalized polyphenylene skeletons. Subsequent thermolysis transforms the polyphenylene backbones into 1D nanoporous carbonaceous frameworks, while the metallic moieties are reduced into Co or Pt nanocrystals, respectively. After removal of the AAO template, 1D NPCs/Co(3)O(4) or NPCs/Pt are obtained, for which structural characterizations reveal that high-quality Co(3)O(4) or Pt nanocrystals are distributed homogeneously within carbon frameworks. These unique 1D metal-carbon hybrids exhibit a promising potential in electrochemical energy storage. NPCs/Co(3)O(4) is evaluated as an electrode material in a supercapacitor, for which Co(3)O(4) nanocrystals contribute an exceptionally high gravimetric capacitance value of 1066 F g(-1). NPCs/Pt is applied as an electrocatalyst showing excellent catalytic efficiency toward methanol oxidation in comparison to commercial E-TEK (Pt/C) catalyst.

Photocatalytic hydrogen evolution through fully conjugated poly(azomethine) networks

Three-dimensional conjugated poly(azomethine) networks were found to be promising candidates for applications in photocatalytic water splitting. Straightforward synthetic protocols lead to fully organic photocatalysts that showed enhanced long-time stability. Furthermore, the catalytic performance of these materials was correlated to the molecular composition and the optoelectronic properties of the samples.

Structurally Defined Graphene Nanoribbons with High Lateral Extension

Oxidative cyclodehydrogenation of laterally extended polyphenylene precursor allowed bottom-up synthesis of structurally defined graphene nanoribbons (GNRs) with unprecedented width. The efficiency of the cyclodehydrogenation was validated by means of MALDI-TOF MS, FT-IR, Raman, and UV-vis absorption spectroscopies as well as investigation of a representative model system. The produced GNRs demonstrated broad absorption extended to near-infrared region with the optical band gap of as low as 1.12 eV.

Nanoporous copolymer networks through multiple Friedel–Crafts-alkylation—studies on hydrogen and methane storage

A novel series of hypercrosslinked copolymer networks was obtained by the statistical co-condensation of 4,4′-bis(chloromethyl)biphenyl with a series of non-functionalized fluorene-based monomers under Friedel–Crafts catalysis. The resulting nanoporous polymer materials exhibit high BET surface areas of up to 1800 m2 g−1 as derived from nitrogen physisorption. The hydrogen and methane uptakes were examined with respect to the chemical composition of these novel polymer adsorbents.

Preparation of Microporous Melamine-based Polymer Networks in an Anhydrous High-Temperature Miniemulsion

We report the first example of a successful preparation of a microporous organic polymer within the droplet phase of an inverse non-aqueous miniemulsion. Stable nanoparticles with enhanced specific surface area could be obtained despite the harsh conditions regarding reaction temperature (180 °C) and time (72 h) needed for building melamine-based Schiff base networks. Our new flexible method can in principle be applied to other water-sensitive protocols suitable for the bulk synthesis of MOPs that are based on Friedel-Crafts, Sonogashira-Hagihara or Yamamoto chemistry.

Molecular Triangles: Synthesis, Self-Assembly, and Blue Emission of Cyclo-7,10-tris-triphenylenyl Macrocycles

A set of cyclo-7,10-tris-triphenylenyl macrocycles have been prepared by a Yamamoto cyclotrimerization protocol. In these novel macrocycles, three triphenylene units are covalently linked to each other, resulting in the formation of triangular-shaped molecules. The fully planar derivative revealed pronounced self-assembly behavior. NMR spectroscopy was used to determine the association constant in solution. 2D wide-angle X-ray scattering was applied to the study of the liquid crystallinity of this new discotic mesogen in the bulk state. Furthermore, nonplanar, laterally substituted derivatives were successfully tested as blue emitters in organic light-emitting diodes owing to their unique optoelectronic properties and their high stability. In this case, substitution with sterically demanding phenyl groups was efficiently used to suppress intermolecular packing, thus preventing undesired quenching effects.

Multicomponent Self-Assembly with a Shape-Persistent N-Heterotriangulene Macrocycle on Au(111)

Multicomponent network formation by using a shape-persistent macrocycle (MC6) at the interface between an organic liquid and Au(111) surface is demonstrated. MC6 serves as a versatile building block that can be coadsorbed with a variety of organic molecules based on different types of noncovalent interactions at the liquid-solid interface. Scanning tunneling microscopy (STM) reveals the formation of crystalline bicomponent networks upon codeposition of MC6 with aromatic molecules, such as fullerene (C60) and coronene. Tetracyanoquinodimethane, on the other hand, was found to induce disorder into the MC6 networks by adsorbing on the rim of the macrocycle. Immobilization of MC6 itself was studied in two different noncovalently assembled host networks. MC6 assumed a rather passive role as a guest and simply occupied the host cavities in one network, whereas it induced a structural transition in the other. Finally, the central cavity of MC6 was used to capture C60 in a complex three-component system. Precise immobilization of organic molecules at discrete locations within multicomponent networks, as demonstrated here, constitutes an important step towards bottom-up fabrication of functional surface-based nanostructures.

Raman Fingerprints of Atomically Precise Graphene Nanoribbons.

Bottom-up approaches allow the production of ultranarrow and atomically precise graphene nanoribbons (GNRs) with electronic and optical properties controlled by the specific atomic structure. Combining Raman spectroscopy and ab initio simulations, we show that GNR width, edge geometry, and functional groups all influence their Raman spectra. The low-energy spectral region below 1000 cm–1 is particularly sensitive to edge morphology and functionalization, while the D peak dispersion can be used to uniquely fingerprint the presence of GNRs and differentiates them from other sp2 carbon nanostructures.

Structural polymorphism in self-assembled networks of a triphenylene based macrocycle

Understanding and controlling the structural polymorphism in self-assembled networks of functional molecules merit special attention. In this contribution, we describe the concentration controlled structural evolution in self-assembled monolayers of a large triangular discotic macrocycle at the liquid-solid interface. Scanning tunneling microscopy (STM) reveals that the adlayers formed by an alkoxy substituted cyclo-tris(7,9-triphenylenylene) macrocycle exhibit concentration dependent 2D phase behavior at the 1,2,4-trichlorobenzene/HOPG interface. The self-assembled network evolves from high-density linear packing which is formed at relatively high concentrations to a low-density porous pattern at lower concentrations. A trimeric hexagonal phase exists at intermediate concentrations examined. The transformation of the trimeric hexagonal phase to the linear phase could be monitored by recording time-dependent STM images. The self-assembly behavior is affected significantly by the choice of the organic solvent where an amorphous network is formed along with high-density linear packing at the 1-phenyloctane/HOPG interface. The results presented here provide detailed insight into the polymorphism phenomenon exhibited by an organic semiconductor and furnish general guidelines to control the morphology of thin films of such technologically important materials.