Yanfei Shen

Self-Assembly Made Durable: Water-Repellent Materials Formed by Cross-Linking Fullerene Derivatives

Fullerene flakes: A diacetylene-functionalized fullerene derivative self-organizes into flakelike microparticles (see picture). Both the diacetylene and C(60) moieties can be effectively cross-linked, which leads to supramolecular materials with remarkable resistivity to solvent, heat, and mechanical stress. Moreover, the surface of the cross-linked flakelike objects is highly durable and water-repellent.

Superstructures and superhydrophobic property in hierarchical organized architectures of fullerenes bearing long alkyl tails

Formation of hierarchically self-organized architectures in organic media and their non-wetting surface features of a series of fullerene-C60 derivatives bearing different numbers of long hydrocarbon chains (1–3) and semiperfluoro-alkyl tails (4) are investigated by means of a variety of techniques, including X-ray diffraction, differential scanning calorimetry, as well as spectroscopic and microscopic methods. All derivatives self-assemble into a bilayer arrangement with their fundamental structural subunit and lamellar distance ranging from 2.88 to 4.85 nm depending on the substituents. The hydrocarbon-C60 derivatives (1–3) provide well-defined three-dimensional microparticles having a nanoflaked outer surface morphology or microparticles composed of many plate-like units in 1,4-dioxane solution, both architectures enhancing the surface water-repellency. The microparticles with a nanoflaked-outer surface obtained from a C60 derivative with semiperfluoro-alkyl chains (4) in a diethoxyethane solution exhibit a surface water-repellency comparable to objects formed from the hydrocarbon-hybrid C60 derivatives. Taking into account the moderate hydrophobic nature of the C60 surface compared to the high hydrophobicity of the hydro- or fluoro-carbons, these results suggest that the C60 moieties are exposed to the outer surface in the supramolecular objects formed in polar solvent conditions and define their non-wetting properties.

Electron Transport and Electrochemistry of Mesomorphic Fullerenes with Long-Range Ordered Lamellae

Fullerenes, C60, modified with long alkyl chains form long-range ordered lamellar mesophases permitting a high C60 content. The mesomorphic fullerenes feature reversible electrochemistry and a comparably high electron carrier mobility making them attractive components for fullerene-based soft materials.

Supramolecular Templates for Nanoflake-Metal Surfaces

A sustainable method for the fabrication of metallic surfaces with flower-like fractal morphology was developed by using a three-dimensional supramolecular assembly as a template. Modifying Au nanoflakes with self-assembled monolayers or polymers allows the surface wettability to be adjusted from superhydrophobic to superhydrophilic (see figure). Furthermore, Au nanoflakes present excellent substrates for surface-enhanced Raman spectroscopy (SERS).

Single-wall carbon nanotube latexes.

A nanolatex copolymer (25−30 nm) of an imidalozium bromide acrylate is reported that provides stable waterborne dispersions of single-walled carbon nanotubes (SWCNT) and thermally and electrically conducting coatings that adhere to plastics. This approach to dispersing SWCNT leaps past previous reports by providing stabilization and binder functions simultaneously. Resulting films exhibit 10-fold anisotropy in both thermal and electrical conductivity and appear free of interfacial phonon scattering problems. The electrically conducting networks assembled upon film formation provide a new route to priming plastics for electrodeposition in addition to providing simple antistatic layer formulations. The efficacy of these nanolatexes is assigned to the imidazolium and bromide components shown in other studies to have an affinity for graphene surfaces.

Photoconductivity and enhanced memory effects in hybrid C60–graphene transistors

We describe the observation of photoconductivity and enhanced memory effects in graphene devices functionalized with clusters of alkylated C(60) molecules. The alkylated C(60) clusters were adsorbed on chemical vapor deposition-grown graphene devices from an aprotic medium. The resulting alkylated C(60)-graphene hybrid devices showed reproducible photoconductive behavior originating from the electron-accepting nature of the C(60) molecules. Significantly enhanced gate hysteresis was observed upon illumination with visible light, thereby enabling the use of C(60)-graphene hybrid devices in three-terminal photo-memory applications.

Assembly of carbon nanotubes and alkylated fullerenes: nanocarbon hybrid towards photovoltaic applications

Taking advantage of the non-covalent interaction between alkyl chains and the sidewalls of a single-walled carbon nanotube (SWCNT), a nanocarbon hybrid of SWCNT and a fullerene (C60) derivative with long alkyl chains was constructed as a donor–acceptor pair for photovoltaics and nanodevice investigations. It was found that SWCNT could be mostly unbundled by the alkylated C60 (1) and was well-dispersed in organic solvents. As a photoactive material, the resultant nanocarbon hybrid, 1-SWCNT, performed well in light-energy harvesting applications in photoelectrochemical cells and nanoscale field-effect transistors (FET). Moreover, the 1-SWCNT assembly exhibited superhydrophobicity, providing an interesting opportunity to fabricate nanocarbon-based waterproof optoelectronic devices. In order to understand the photoexcitation process, the 1-SWCNT assembly was electrochemically and spectroscopically characterized. The electrochemical results showed that the SWCNT facilitated electronic communication between 1 and the electrode. The steady-state and time-resolved fluorescence and the photoluminescence excitation studies suggested efficient quenching of the singlet excited state of C60. Nanosecond transient absorption data revealed the one-electron reduction of fullerene, C60˙−, thereby demonstrating the photoinduced electron transfer from SWCNT to the C60 unit in the 1-SWCNT assembly.

Microstructured objects produced by the supramolecular hierarchical assembly of an organic free radical gathering hydrophobic-amphiphilic characteristics

The different weak non-covalent interactions established between “hydrophobic–amphiphilic” fluorescent and paramagnetic organic free-radical molecules, and solvents result in the formation of hierarchically self-assembled multifunctional superhydrophobic materials with very unusual shapes.

Nanoplasmonic modification of the local morphology, shape, and wetting properties of nanoflake microparticles

Inducing a phase transition of a self-organized object may trigger its structural transformation. Here, we demonstrate local control of the morphology and shape of self-organized microparticles with a nanoflake outer surface by nanoplasmonic heating. To increase the photothermal efficiency of the microparticles, gold nanoparticles (AuNPs) or single-walled carbon nanotubes (SWCNTs) were incorporated. AuNPs and SWCNTs, which have excellent photothermal activity, acts as photoresponsive heat converters. Because they have distinct absorption characteristics, visible or near-infrared lasers can be used to induce local heating. The photothermal effect was used to spatially confine the melting to the space within the particle and the aggregate; as a result, microparticles with various shapes and morphologies have been fabricated. Such morphological changes lead to a superhydrophobic-hydrophobic wetting transition, which was confirmed by the films constituting the microparticles. The work presented is seen useful for anisotropic particle synthesis, local wetting control, lithography, and morphological control of functional materials.

Exotic Self-Organized Fullerene Materials Based on Uncommon Hydrophobic–Amphiphilic Approach

This review documents the recent developments of supramolecular materials composed of alkylated fullerenes (C60) which have a unique hydrophobic amphiphilicity. Unlike the conventional amphiphiles composed of hydrophilic and hydrophobic units, the alkyl-conjugated C60 derivatives presented here contain two hydrophobic moieties, C60 and alkyl tails. Slightly different hydrophobicity and chemical nature make them arranged into microphase-segregated mesostructures with lamella units in nanometer scale, which mainly relies on the relatively weak interactions, π–π in neighboring C60 molecules, and van der Waals between alkyl chains. These molecular assemblies and supramolecular arrays feature distinct dimensionality and morphologies, namely exotic assemblies, as a consequence of the presence of different assembly environment, and different number and length of the alkyl chains, as well as the position of the substitutions. The systematic exploration of the molecular design and preparative methodologies for new versatile supramolecular materials will be reviewed in details.