Fuke Wang

Some recent developments of polyhedral oligomeric silsesquioxane (POSS)-based polymeric materials

Polyhedral Oligomeric Silsesquioxane (POSS) has attracted considerable interest in materials science due to its well-defined nano-scale organic–inorganic structure, which makes it an ideal building block for constructing nano-structured hybrid materials and nanocomposites. In this article, we highlight some recent developments in applications of POSS materials: 1) improving thermal and mechanical properties of polymers through incorporation of POSS into polymer matrices to form nanocomposites; 2) using POSS as a building block for design and synthesis of POSS-containing organic semiconductor materials to achieve high photo-luminescence/electron luminescence quantum efficiency in organic light emitting diodes and enhanced performance in electrochromatic devices; 3) exploiting POSS as a hydrophobic unit to develop amphiphilic polymers for drug/gene delivery and formation of hydrogels. A future direction for the development of POSS-containing materials is also proposed for applications in organic photovoltaic and other high-performance materials.

Azulene-containing organic chromophores with tunable near-IR absorption in the range of 0.6 to 1.7 μm

Near-infrared (NIR) absorption in the range of 0.75–2.5 μm is in great demand for a variety of applications but currently the majority of commercial NIR devices are based on inorganic materials due to the limited number of organic materials that are active in this range. Here we present the preparation and optical studies of a new series of stable azulene-containing NIR chromophores whose absorption can be tuned in the range of 0.6–1.7 μm. DFT calculation revealed that the protonation-induced low excitation gap was attributable to the substantial intramolecular charge transfer.

Surface-functionalized silica-coated gold nanoparticles and their bioapplications

Monodisperse Au at SiO(2) nanoparticles has been functionalized with carboxylic groups for further bioconjugation with amino-terminated oligonucleotides. The oligonucleotide-modified Au at SiO(2) nanoprobes have been applied in the fast colorimetric DNA based on the sequence-specific hybridization properties of DNA. Self-assembling behavior of Au at SiO(2) nanoparticles was also investigated.

Highly Sensitive and Fast Response Colorimetric Humidity Sensors Based on Graphene Oxides Film

Uniform graphene oxide (GO) film for optical humidity sensing was fabricated by dip-coating technique. The resulting GO thin film shows linear optical shifts in the visible range with increase of humidity in the whole relative humidity range (from dry state to 98%). Moreover, GO films exhibit ultrafast sensing to moisture within 250 ms because of the unique atomic thinness and superpermeability of GO sheets. The humidity sensing mechanism was investigated using XRD and computer simulation. The ultrasensitive humidity colorimetric properties of GOs film may enable many potential applications such as disposable humidity sensors for packaging, health, and environmental monitoring.

Directed Self-Assembly of Densely Packed Gold Nanoparticles

Directing the self-assembly of sub-10-nm nanoparticles has been challenging because of the simultaneous requirements to achieve a densely packed monolayer and rearrange nanoparticles to assemble within a template. We met both requirements by separating the processes into two steps by first forming a monolayer of gold nanoparticles on a suitable liquid subphase of anisole and then transferring it edgewise onto a silicon substrate with a prepatterned template comprising nanoposts and nanogratings. Doing so resulted in nanoparticles that assembled in commensuration with the template design while exhibiting appreciable template-induced strain. These dense arrays of nanostructures could either be directly applied or used as lithographic masks in applications for light collection, chemical sensing, and data storage.

Polyhedral oligomeric silsesquioxanes (POSSs): an important building block for organic optoelectronic materials

Due to the low-cost, facile processability and the capability of producing large areas of flexible thin films, organic optoelectronic materials have been considered among the most promising materials in the past two decades in both academic research and industry applications. Particularly, the incorporation of polyhedral oligomeric silsesquioxanes (POSSs) to develop high performance organic optoelectronic materials and the fabrication of these sophisticated materials into highly efficient devices are of significant interest because of the unique hybrid structures and physical properties of POSS. In this review, we present the recent advances in the development of POSS-based organic optoelectronic materials and devices, including organic light-emitting diodes (OLEDs), liquid crystal display, sensors and electrochromic devices. In addition, the insights into the uniqueness of POSS in microstructure, confined size effect, and their different organic substituents in the enhancement of the optoelectronic performance are illustrated. Finally, perspectives and challenges related to the further advancement of POSS-based organic optoelectronic materials are discussed, followed by the proposed design considerations to address the challenges that we will face in the future.

Azulene-based conjugated polymers with tuneable near-IR absorption up to 2.5 μm

A series of near-IR-active conjugated polymers that cover the near-IR spectrum ranging from 1.0 to 2.5 μm were reported. Polymers based on an alternating π-conjugated donor and acceptor backbone were designed and protonated azulene was chosen as an efficient acceptor due to the excellent stability of the azulenylium ion. The absorption at 2.5 μm achieved in this study is by far the longest reported for stable near-IR responsive conjugative polymers. The resulting polymers exhibit good solubility and thermal stability, and easy film formation characteristics, which are important for device applications. The near-IR absorption bands were attributed to the intramolecular charge transfer transition, which was confirmed by our DFT calculations. Electrochromic devices constructed using these materials showed stable and high optical contrast, demonstrating the potential application of these polymers in building organic-based near-IR devices.

Template-Induced Structure Transition in Sub-10 nm Self-Assembling Nanoparticles

We report on the directed self-assembly of sub-10 nm gold nanoparticles confined within a template comprising channels of gradually varying widths. When the colloidal lattice parameter is mismatched with the channel width, the nanoparticles rearrange and break their natural close-packed ordering, transiting through a range of structural configurations according to the constraints imposed by the channel. While much work has been done in assembling ordered configurations, studies of the transition regime between ordered states have been limited to microparticles under applied compression. Here, with coordinated experiments and Monte Carlo simulations we show that particles transit through a more diverse set of self-assembled configurations than observed for compressed systems. The new insight from this work could lead to the control and design of complex self-assembled patterns other than periodic arrays of ordered particles.

Near-infrared responsive conjugated polymers to 1.5 μm and beyond: synthesis and electrochromic switching application.

Azulene-containing conjugated polymers with near-infrared absorption up to 1.5 μm and beyond are achieved by treating with trifluoroacetic acid (TFA). Density functional theory calculations reveal that the near-infrared absorption arises from a strong intramolecular charge transfer transition on the polymer backbone, and the near-infrared absorption can be tuned by the degree of protonation. Furthermore, TFA treated polymers show a ten-fold enhancement in electrochromic contrast and significantly improved switching stability, suggesting that these polymers are promising candidates for fabrication of the first generation organic near-infrared devices.

Origin of Near-Infrared Absorption for Azulene-Containing Conjugated Polymers upon Protonation or Oxidation.

A series of azulene-containing conjugated polymers were studied to elucidate their tunable absorption properties in near-infrared (NIR) regions (i.e., 1.2-2.5 μm) upon protonation/oxidation. Density function theory (DFT) revealed that protonation-induced intramolecular charge transfer (ICT) in the polymer backbone lead to strong NIR absorption. Distinct spectral change was observed when tiny amount of peroxide was added to the protonated polymer in trifluoroacetic acid/chloroform solution. Electron paramagnetic resonance (EPR) study confirmed the presence of radical cation, which results in the occurrence of newly formed absorption band after the addition of peroxide. The spectro-electrochemical results and DFT study indicate that polarons and polaron pairs were formed during p-doping process, and both the chemical oxidation and electrochemical oxidation could be facilitated by TFA protonation. This represents the first reported mechanisms of NIR absorption under various protonation/oxidation conditions in a single polymer system.