Glycosylated Oligo(ethynylene)s via a Pd/Zn-Mediated Cross-Coupling Reaction

The synthesis of higher oligo(ethynylene)s represents a challenge in modern organic chemistry, because of their decreasing stability with increasing length and side-product formation during the reaction. Recently, we reported the development of a mild and convenient sp–sp carbon heterocoupling protocol for the preparation of glycosylated oligo(ethynylene)s based on the Negishi reaction. The application of this protocol in combination with a one-step desilylation-bromination allowedfor the sequential synthesis of glycosylated oligo(ethynylene)s up to the octayne

Soft-landing electrospray ion beam deposition of sensitive oligoynes on surfaces in vacuum

AbstractAdvances in synthetic chemistry permit the synthesis of large, highly functional, organic molecules. Characterizing the complex structure of such molecules with highly resolving, vacuum-based methods like scanning probe microscopy requires their transfer into the gas phase and further onto an atomically clean surface in ultrahigh vacuum without causing additional contamination. Conventionally this is done via sublimation in vacuum. However, similar to biological molecules, large synthetic compounds can be non-volatile and decompose upon heating. Soft-landing ion beam deposition using soft ionization methods represents an alternative approach to vacuum deposition. Using different oligoyne derivatives of the form of R1(CC)nR2, here we demonstrate that even sensitive molecules can be handled by soft-landing electrospray ion beam deposition. We generate intact molecular ions as well as fragment ions with intact hexayne parts and deposit them on clean metal surfaces. Scanning tunneling microscopy shows that the reactive hexayne segments of the molecules of six conjugated triple bonds are intact. The molecules agglomerate into ribbon-like islands, whose internal structure can be steered by the choice of the substituents. Our results suggest the use of ion beam deposition to arrange reactive precursors for subsequent polymerization reactions

Nanostructured Carbonaceous Materials from Molecular Precursors

Nanostructured carbonaceous materials, that is, carbon materials with a feature size on the nanometer scale and, in some cases, functionalized surfaces, already play an important role in a wide range of emerging fields, such as the search for novel energy sources, efficient energy storage, sustainable chemical technology, as well as organic electronic materials. Furthermore, such materials might offer solutions to the challenges associated with the on-going depletion of nonrenewable energy resources or climate change, and they may promote further breakthroughs in the field of microelectronics. However, novel methods for their preparation will be required that afford functional carbon materials with controlled surface chemistry, mesoscopic morphology, and microstructure. A highly promising approach for the synthesis of such materials is based on the use of well-defined molecular precursors. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Synthesis and Characterization of Gyroidal Mesoporous Carbons and Carbon Monoliths with Tunable Ultralarge Pore Size

Ordered mesoporous carbons with high pore accessibility are of great interest as electrodes in energy conversion and storage applications due to their high electric and thermal conductivity, chemical inertness, and low density. The metal- and halogen-free synthesis of gyroidal bicontinuous mesoporous carbon materials with uniform and tunable pore sizes through bottom-up self-assembly of block copolymers thus poses an interesting challenge. Four double gyroidal mesoporous carbons with pore sizes of 12, 15, 20, and 39 nm were synthesized using poly(isoprene)-<i>block</i>-poly(styrene)-<i>block</i>-poly(ethylene oxide) (ISO) as structure-directing triblock terpolymer and phenol–formaldehyde resols as carbon precursors. The highly ordered materials were thermally stable to at least 1600 °C with pore volumes of up to 1.56 cm³ g^–1. Treatment at this temperature induced a high degree of sp²-hybridization and low microporosity. Increasing the resols/ISO ratio led to hexagonally packed cylinders with lower porosity. A single gyroid carbon network with high porosity of 80 vol % was obtained using a similar synthesis strategy. Furthermore, we present a method to fabricate monolithic materials of the gyroidal carbons with macroscopic shape and thickness control that exhibit an open and structured surface with gyroidal features. The gyroidal materials are ideally suited as electrode materials in fuel cells, batteries, and supercapacitors as their high, three-dimensionally connected porosity is expected to allow for good fuel or electrolyte accessibility and to prevent total pore blockage

Facile synthesis of oligoyne amphiphiles and their rotaxanes

Carbon-rich organic compounds containing a series of conjugated triple bonds (oligoynes) are relevant synthetic targets, but an improved access to oligoynes bearing functional groups would be desirable. Here, we report the straightforward synthesis of two series of oligoyne amphiphiles with glycoside or carboxylate polar head groups, investigate their self-assembly behavior in aqueous media, and their use as precursors for the formation of oligoyne rotaxanes with cyclodextrin hosts. To this end, we employed mono-, di-, or triacetylenic building blocks that gave access to the corresponding zinc acetylides in situ and allowed for the efficient elongation of the oligoyne segment in few synthetic steps via a Negishi coupling protocol. Moreover, we show that the obtained oligoyne derivatives can be deprotected to yield the corresponding amphiphiles. Depending on their head groups, the supramolecular self-assembly of these amphiphiles gave rise to different types of carbon-rich colloidal aggregates in aqueous media. Furthermore, their amphiphilicity was exploited for the preparation of novel oligoyne cyclodextrin rotaxanes using simple host-guest chemistry in water

Low-Temperature Preparation of Tailored Carbon Nanostructures in Water

The development of low-temperature carbonization procedures promises to provide novel nanostructured carbon materials that are of high current interest in materials science and technology. Here, we report a "wet-chemical" carbonization method that utilizes hexayne amphiphiles as metastable carbon precursors. Nearly perfect control of the nanoscopic morphology was achieved by self-assembly of the precursors into colloidal aggregates with tailored diameter in water. Subsequent carbonization furnished carbon nanocapsules with a carbon microstructure resembling graphite-like amorphous carbon materials

Formation of Periodically-Ordered Calcium Phosphate Nanostructures by Block Copolymer-Directed Self-Assembly

Structuring ionic solids at the nanoscale with block copolymers (BCPs) is notoriously difficult due to solvent incompatibilities and strong driving forces for crystallization of the inorganic material. Here, we demonstrate that elucidating pathway complexity in the BCP-directed self-assembly of an ionic solid, amorphous calcium phosphate (ACP), is a key component in obtaining nanostructured, <i>bulk</i> composite materials in which the nanostructure is the result of thermodynamically controlled BCP self-assembly, i.e., exhibiting sequences of bulk morphologies as known from typical equilibrium BCP phase diagrams. Specifically, we identify three critical pathway “decision points” for the evaporation-induced self-assembly of composites from ultrasmall, organosilicate-modified amorphous calcium phosphate nanoparticles (osm-ACP-NPs) and poly­(isoprene)-<i>block</i>-poly­(2-(dimethylamino)­ethyl methacrylate) (PI-<i>b</i>-PDMAEMA) block copolymers. Using this strategy enabled us to obtain composites with hexagonal, cubic network, and lamellar BCP morphologies, in addition to mesoporous, cellular materials and macrophase separated materials. The osm-ACP-NPs are synthesized via a two-step sol–gel process in which (3-glycidyloxypropyl)­trimethoxysilane (GLYMO) quenches the reaction, limits the particle size, and functionalizes the NP surface. Dynamic light scattering evidences a transition from BCP unimers to micellar aggregates with increasing amounts of sol solution, which is reflected by a corresponding switch from BCP-type morphologies to micellar/cellular morphologies of the nanocomposites. Nanostructured organic–inorganic composites with a continuous osm-ACP-NP matrix phase have indentation moduli (measured by nanoindentation) that are an order of magnitude larger than unstructured composites with similar compositions. Insights provided by this study have relevance to understanding the effects of pathway complexity in the assembly of organic–inorganic composites and may enable access to a broad range of hybrid nanostructures with potential applications in areas including dental repair and hard tissue engineering