Aggregate nanostructures of organic molecular materials

Conjugated organic molecules are interesting materials because of their structures and their electronic, electrical, magnetic, optical, biological, and chemical properties. However, researchers continue to face great challenges in the construction of well-defined organic compounds that aggregate into larger molecular materials such as nanowires, tubes, rods, particles, walls, films, and other structural arrays. Such nanoscale materials could serve as direct device components. In this Account, we describe our recent progress in the construction of nanostructures formed through the aggregation of organic conjugated molecules and in the investigation of the optical, electrical, and electronic properties that depend on the size or morphology of these nanostructures. We have designed and synthesized functional conjugated organic molecules with structural features that favor assembly into aggregate nanostructures via weak intermolecular interactions. These large-area ordered molecular aggregate nanostructures are based on a variety of simpler structures such as fullerenes, perylenes, anthracenes, porphyrins, polydiacetylenes, and their derivatives. We have developed new methods to construct these larger structures including organic vapor-solid phase reaction, natural growth, association via self-polymerization and self-organization, and a combination of self-assembly and electrochemical growth. These methods are both facile and reliable, allowing us to produce ordered and aligned aggregate nanostructures, such as large-area arrays of nanowires, nanorods, and nanotubes. In addition, we can synthesize nanoscale materials with controlled properties. Large-area ordered aggregate nanostructures exhibit interesting electrical, optical, and optoelectronic properties. We also describe the preparation of large-area aggregate nanostructures of charge transfer (CT) complexes using an organic solid-phase reaction technique. By this process, we can finely control the morphologies and sizes of the organic nanostructures on wires, tubes, and rods. Through field emission studies, we demonstrate that the films made from arrays of CT complexes are a new kind of cathode materials, and we systematically investigate the effects of size and morphology on electrical properties. Low-dimension organic/inorganic hybrid nanostructures can be used to produce new classes of organic/inorganic solid materials with properties that are not observed in either the individual nanosize components or the larger bulk materials. We developed the combined self-assembly and templating technique to construct various nanostructured arrays of organic and inorganic semiconductors. The combination of hybrid aggregate nanostructures displays distinct optical and electrical properties compared with their individual components. Such hybrid structures show promise for applications in electronics, optics, photovoltaic cells, and biology. In this Account, we aim to provide an intuition for understanding the structure-function relationships in organic molecular materials. Such principles could lead to new design concepts for the development of new nonhazardous, high-performance molecular materials on aggregate nanostructures.     

Functional micro/nanostructures: simple synthesis and application in sensors, fuel cells, and gene delivery

In order to develop new, high technology devices for a variety of applications, researchers would like to better control the structure and function of micro/nanomaterials through an understanding of the role of size, shape, architecture, composition, hybridization, molecular engineering, assembly, and microstructure. However, researchers continue to face great challenges in the construction of well-defined micro/nanomaterials with diverse morphologies. At the same time, the research interface where micro/nanomaterials meet electrochemistry, analytical chemistry, biomedicine, and other fields provides rich opportunities to reveal new chemical, physical, and biological properties of micro/nanomaterials and to uncover many new functions and applications of these materials. In this Account, we describe our recent progress in the construction of novel inorganic and polymer nanostructures formed through different simple strategies. Our synthetic strategies include wet-chemical and electrochemical methods for the controlled production of inorganic and polymer nanomaterials with well-defined morphologies. These methods are both facile and reliable, allowing us to produce high-quality micro/nanostructures, such as nanoplates, micro/nanoflowers, monodisperse micro/nanoparticles, nanowires, nanobelts, and polyhedron and even diverse hybrid structures. We implemented a series of approaches to address the challenges in the preparation of new functional micro/nanomaterials for a variety of important applications This Account also highlights new or enhanced applications of certain micro/nanomaterials in sensing applications. We singled out analytical techniques that take advantage of particular properties of micro/nanomaterials. Then by rationally tailoring experimental parameters, we readily and selectively obtained different types of micro/nanomaterials with novel morphologies with high performance in applications such as electrochemical sensors, electrochemiluminescent sensors, gene delivery agents, and fuel cell catalysts. We expect that micro/nanomaterials with unique structural characteristics, properties, and functions will attract increasing research interest and will lead to new opportunities in various fields of research.     

Bionanoparticles as functional macromolecular building blocks - A new class of nanomaterials

We would like to introduce bionanoparticles with their unique multifunctional and self-assembling properties. Particularly, protein cages like plant viruses or ferritin but also other well-defined self-assembling protein structural motifs are valuable building blocks with great potential in (bio-) nanotechnology. A steeply increasing number of research works present promising results and applications in biomedicine, diagnostics and analytics as well as nanoelectronics. However, the use of bionanoparticles for hybrid and soft protein-polymer composite materials has not received high attention yet. The article will first introduce the structural principles of well-defined protein complexes and exemplarily describe the structure of a few selected plant viruses and ferritin. Then, the recent progress in chemical or genetically programmed functionalization and the use of the modified bionanoparticles for the production of novel nanostructured (hybrid) materials will be presented. An updated overview of grafting-onto and grafting-from polymerization methods for the modification of proteins and protein complexes will be given as well. The feature closes with some exciting examples in which bio (in-) organic nanoparticles are employed in analytics, for catalysis and biomedical applications.     

Conjugated-polymer grafting on inorganic and organic substrates: A new trend in organic electronic materials

This review highlights recent developments in the grafting of conjugated polymers onto various substrates for organic electronic devices. The rapid development of multi-layer architectures demands the preparation of well-defined interfaces between both compatible and incompatible materials. It is promising therefore that interface-engineering is now known to help passivate charge trap states, control energy level alignments, enhance charge extraction, guide active-layer morphologies, and improve material compatibility, adhesion and device stability. In organic electronic devices, conjugated polymers are in contact with a wide range of constituents, such as metals, metal oxides, organic materials, and inorganic particles. Covalent bonds between these materials and macromolecules are desired to yield intimate contacts and well-defined interfaces. Following an overview of the various synthetic methodologies of conjugated polymers, the chemistry of tethering macromolecular chains onto nanoparticles and flat surfaces is described. The creation of functional hybrid materials offers the potential to deliver efficient and low-cost devices.     

Multifunctional mesoporous silica nanocomposite nanoparticles for theranostic applications

Clever combinations of different types of functional nanostructured materials will enable the development of multifunctional nanomedical platforms for multimodal imaging or simultaneous diagnosis and therapy. Mesoporous silica nanoparticles (MSNs) possess unique structural features such as their large surface areas, tunable nanometer-scale pore sizes, and well-defined surface properties. Therefore, they are ideal platforms for constructing multifunctional materials that incorporate a variety of functional nanostructured materials. In this Account, we discuss recent progress by our group and other researchers in the design and fabrication of multifunctional nanocomposite nanoparticles based on mesoporous silica nanostructures for applications to simultaneous diagnosis and therapy. Versatile mesoporous silica-based nanocomposite nanoparticles were fabricated using various methods. Here, we highlight two synthetic approaches: the encapsulation of functional nanoparticles within a mesoporous silica shell and the assembly of nanoparticles on the surface of silica nanostructures. Various nanoparticles were encapsulated in MSNs using surfactants as both phase transfer agents and pore-generating templates. Using MSNs as a scaffold, functional components such as magnetic nanoparticles and fluorescent dyes have been integrated within these systems to generate multifunctional nanocomposite systems that maintain their individual functional characteristics. For example, uniform mesoporous dye-doped silica nanoparticles immobilized with multiple magnetite nanocrystals on their surfaces have been fabricated for their use as a vehicle capable of simultaneous magnetic resonance (MR) and fluorescence imaging and drug delivery. The resulting nanoparticle-incorporated MSNs were then tested in mice with tumors. These in vivo experiments revealed that these multifunctional nanocomposite nanoparticles were delivered to the tumor sites via passive targeting. These nanocomposite nanoparticles served as successful multimodal imaging probes and also delivered anticancer drugs to the tumor site. With innumerable combinations of imaging modalities and drug delivery available within these vehicles, multifunctional nanocomposite nanoparticles provide new opportunities for clinical diagnostics and therapeutics.     

Inorganic nanostructures grown on graphene layers

This article presents a review of current research activities on the hybrid heterostructures of inorganic nanostructures grown directly on graphene layers, which can be categorized primarily as zero-dimensional nanoparticles; one-dimensional nanorods, nanowires, and nanotubes; and two-dimensional nanowalls. For the hybrid structures, the nanostructures exhibit excellent material characteristics including high carrier mobility and radiative recombination rate as well as long-term stability while graphene films show good optical transparency, mechanical flexibility, and electrical conductivity. Accordingly, the versatile and fascinating properties of the nanostructures grown on graphene layers make it possible to fabricate high-performance optoelectronic and electronic devices even in transferable, flexible, or stretchable forms. Here, we review preparation methods and possible device applications of the hybrid structures consisting of various types of inorganic nanostructures grown on graphene layers.     

Novel hybrid organic/inorganic 2D quasiperiodic PC: from diffraction pattern to vertical light extraction

Recently, important efforts have been dedicated to the realization of a fascinating class of new photonic materials or metamaterials, known as photonic quasicrystals (PQCs), in which the lack of the translational symmetry is compensated by rotational symmetries not achievable by the conventional periodic crystals. As ever, more advanced functionality is demanded and one strategy is the introduction of non-linear and/or active functionality in photonic materials. In this view, core/shell nanorods (NRs) are a promising active material for light-emitting applications. In this article a two-dimensional (2D) hybrid a 2D octagonal PQC which consists of air rods in an organic/inorganic nanocomposite is proposed and experimentally demonstrated. The nanocomposite was prepared by incorporating CdSe/CdS core/shell NRs into a polymer matrix. The PQC was realized by electron beam lithography (EBL) technique. Scanning electron microscopy, far field diffraction and spectra measurements are used to characterize the experimental structure. The vertical extraction of the light, by the coupling of the modes guided by the PQC slab to the free radiation via Bragg scattering, consists of a narrow red emissions band at 690 nm with a full width at half-maximum (FWHM) of 21.5 nm. The original characteristics of hybrid materials based on polymers and colloidal NRs, able to combine the unique optical properties of the inorganic moiety with the processability of the host matrix, are extremely appealing in view of their technological impact on the development of new high performing optical devices such as organic light-emitting diodes, ultra-low threshold lasers, and non-linear devices.PACS: 81.07.Pr Organic-inorganic hybrid nanostructures, 81.16.-c Methods of nanofabrication and processing, 42.70.Qs Photonic band-gap materials.     

Supramolecular Materials from Inorganic Building Blocks

Inorganic materials of nanometric dimensions and controllable morphologies are now widely available permitting their use as building blocks in supramolecular structures. Incorporation of inorganic blocks into hybrid structures can yield unique materials that have no naturally occurring or organic synthetic analogues. In this short review, we describe the construction and functions of supramolecular materials prepared using inorganic building blocks, with emphasis on material-like components. Examples described in this review are categorized as (i) inorganic structures within organic assemblies (silica-supported Langmuir monolayers, organic–inorganic lipid bilayer vesicles etc.), (ii) organic components in inorganic nanospaces (mesoporous materials including biocomponents such as peptides and proteins), (iii) organic/inorganic nanohybrid blends (nanorod-liquid crystal blends and surfactant-guided gold nanostructures), and (iv) hierarchic structures (layer-by-layer assemblies of mesoporlous carbons and capsules).     

Synthesis and optimization strategies of nanostructured metal oxides for chemiresistive methanol sensors

Thanks to the merits such as high specific surface areas, superior electronic conduction and unique gas diffusion path derived from the nanoscales, the demand for detecting methanol has contributed to the rapid expansion of gas sensors based on metal oxide nanostructures. In this review, the “process-structure-performance” correlations of metal oxide nanostructures utilized in the detection of methanol are analyzed. The sensing mechanisms of nanostructured metal oxides operated at different temperatures for methanol monitoring are first introduced. Subsequently, various synthesis processes (e.g. hydrothermal, sol-gel and electrospinning) utilized to modulate the structure and morphology of metal oxide nanostructures are discussed. Given the limitations that existed in methanol gas sensors, numerous optimization strategies including doping, surface modifications, newly designed structures and morphologies, the self-doping defects are enumerated to dramatically enhance the sensing properties represented by the improvement of sensitivity, the reduction of working temperature, the decrease of detection limit, etc. Additionally, the challenges and future research directions of advanced methanol sensors based on metal oxide nanostructures are proposed. It is ultimately expected that this review will help break the bottleneck of nanostructured metal oxides gas sensors in the field of methanol detection, and further promote the actual application of chemiresistive methanol sensors.     

The importance of chemistry in creating well-defined nanoscopic embedded therapeutics: devices capable of the dual functions of imaging and therapy

Nanomedicine is a rapidly evolving field, for which polymer building blocks are proving useful for the construction of sophisticated devices that provide enhanced diagnostic imaging and treatment of disease, known as theranostics. These well-defined nanoscopic objects have high loading capacities, can protect embedded therapeutic cargo, and offer control over the conditions and rates of release. Theranostics also offer external surface area for the conjugation of ligands to impart stealth characteristics and/or direct their interactions with biological receptors and provide a framework for conjugation of imaging agents to track delivery to diseased site(s). The nanoscopic dimensions allow for extensive biological circulation. The incorporation of such multiple functions is complicated, requiring exquisite chemical control during production and rigorous characterization studies to confirm the compositions, structures, properties, and performance. We are particularly interested in the study of nanoscopic objects designed for treatment of lung infections and acute lung injury, urinary tract infections, and cancer. This Account highlights our work over several years to tune the assembly of unique nanostructures. We provide examples of how the composition, structure, dimensions, and morphology of theranostic devices can tune their performance as drug delivery agents for the treatment of infectious diseases and cancer. The evolution of nanostructured materials from relatively simple overall shapes and internal morphologies to those of increasing complexity is driving the development of synthetic methodologies for the preparation of increasingly complex nanomedicine devices. Our nanomedicine devices are derived from macromolecules that have well-defined compositions, structures, and topologies, which provide a framework for their programmed assembly into nanostructures with controlled sizes, shapes, and morphologies. The inclusion of functional units within selective compartments/domains allows us to create (multi)functional materials. We employ combinations of controlled radical and ring-opening polymerizations, chemical transformations, and supramolecular assembly to construct such materials as functional entities. The use of multifunctional monomers with selective polymerization chemistries affords regiochemically functionalized polymers. Further supramolecular assembly processes in water with further chemical transformations provide discrete nanoscopic objects within aqueous solutions. This approach echoes processes in nature, whereby small molecules (amino acids, nucleic acids, saccharides) are linked into polymers (proteins, DNA/RNA, polysaccharides, respectively) and then those polymers fold into three-dimensional conformations that can lead to nanoscopic functional entities.     

Solid‐state dye‐sensitized and bulk heterojunction solar cells using TiO2 and ZnO nanostructures: recent progress and new concepts at the borderline

In the field of photovoltaic energy conversion, hybrid inorganic/organic devices represent promising alternatives to standard photovoltaic systems in terms of exploiting the specific features of both organic semiconductors and inorganic nanomaterials. Two main categories of hybrid solar cells coexist today, both of which make much use of metal oxide nanostructures based on titanium dioxide (TiO₂) and zinc oxide (ZnO) as electron transporters. These metal oxides are cheap to synthesise, are non‐toxic, are biocompatible and have suitable charge transport properties, all these features being necessary to demonstrate highly efficient solar cells at low cost. Historically, the first hybrid approach developed was the dye‐sensitized solar cell (DSSC) concept based on a nanostructured porous metal oxide electrode sensitized by a molecular dye. In particular, solid‐state hybrid DSSCs, which reduce the complexity of cell assembly, demonstrate very promising performance today. The second hybrid approach exploits the bulk heterojunction (BHJ) concept, where conjugated polymer/metal oxide interfaces are used to generate photocurrent. In this context, we review the recent progress and new concepts in the field of hybrid solid‐state DSSC and BHJ solar cells based on TiO₂ and ZnO nanostructures, incorporating dyes and conjugated polymers. We point out the specificities in common hybrid device structures and give an overview on new concepts, which couple and exploit the main advantages of both DSSC and BHJ approaches. In particular, we show that there is a trend of convergence between both DSSC and BHJ approaches into mixed concepts at the borderline which may allow in the near future the development of hybrid devices for competitive photovoltaic energy conversion. Copyright © 2011 Society of Chemical Industry     

Investigation of a Mesoporous Silicon Based Ferromagnetic Nanocomposite

A semiconductor/metal nanocomposite is composed of a porosified silicon wafer and embedded ferromagnetic nanostructures. The obtained hybrid system possesses the electronic properties of silicon together with the magnetic properties of the incorporated ferromagnetic metal. On the one hand, a transition metal is electrochemically deposited from a metal salt solution into the nanostructured silicon skeleton, on the other hand magnetic particles of a few nanometres in size, fabricated in solution, are incorporated by immersion. The electrochemically deposited nanostructures can be tuned in size, shape and their spatial distribution by the process parameters, and thus specimens with desired ferromagnetic properties can be fabricated. Using magnetite nanoparticles for infiltration into porous silicon is of interest not only because of the magnetic properties of the composite material due to the possible modification of the ferromagnetic/superparamagnetic transition but also because of the biocompatibility of the system caused by the low toxicity of both materials. Thus, it is a promising candidate for biomedical applications as drug delivery or biomedical targeting.     

Towards nano-organic chemistry: perspectives for a bottom-up approach to the synthesis of low-dimensional carbon nanostructures

Low-dimensional carbon nanostructures, such as nanotubes and graphenes, represent one of the most promising classes of materials, in view of their potential use in nanotechnology. However, their exploitation in applications is often hindered by difficulties in their synthesis and purification. Despite the huge efforts by the research community, the production of nanostructured carbon materials with controlled properties is still beyond reach. Nonetheless, this step is nowadays mandatory for significant progresses in the realization of advanced applications and devices based on low-dimensional carbon nanostructures. Although promising alternative routes for the fabrication of nanostructured carbon materials have recently been proposed, a comprehensive understanding of the key factors governing the bottom-up assembly of simple precursors to form complex systems with tailored properties is still at its early stages. In this paper, following a survey of recent experimental efforts in the bottom-up synthesis of carbon nanostructures, we attempt to clarify generalized criteria for the design of suitable precursors that can be used as building blocks in the production of complex systems based on sp(2) carbon atoms and discuss potential synthetic strategies. In particular, the approaches presented in this feature article are based on the application of concepts borrowed from traditional organic chemistry, such as valence-bond theory and Clar sextet theory, and on their extension to the case of complex carbon nanomaterials. We also present and discuss a validation of these approaches through first-principle calculations on prototypical systems. Detailed studies on the processes involved in the bottom-up fabrication of low-dimensional carbon nanostructures are expected to pave the way for the design and optimization of precursors and efficient synthetic routes, thus allowing the development of novel materials with controlled morphology and properties that can be used in technological applications.     

Investigation of the effect of the structure of large-area carbon nanotube/fuel composites on energy generation from thermopower waves

Thermopower waves are a recently developed energy conversion concept utilizing dynamic temperature and chemical potential gradients to harvest electrical energy while the combustion wave propagates along the hybrid layers of nanomaterials and chemical fuels. The intrinsic properties of the core nanomaterials and chemical fuels in the hybrid composites can broadly affect the energy generation, as well as the combustion process, of thermopower waves. So far, most research has focused on the application of new core nanomaterials to enhance energy generation. In this study, we demonstrate that the alignment of core nanomaterials can significantly influence a number of aspects of the thermopower waves, while the nanomaterials involved are identical carbon nanotubes (CNTs). Diversely structured, large-area CNT/fuel composites of one-dimensional aligned CNT arrays (1D CNT arrays), randomly oriented CNT films (2D CNT films), and randomly aggregated bulk CNT clusters (3D CNT clusters) were fabricated to evaluate the energy generation, as well as the propagation of the thermal wave, from thermopower waves. The more the core nanostructures were aligned, the less inversion of temperature gradients and the less cross-propagation of multiple thermopower waves occurred. These characteristics of the aligned structures prevented the cancellation of charge carrier movements among the core nanomaterials and produced the relative enhancement of the energy generation and the specific power with a single-polarity voltage signal. Understanding this effect of structure on energy generation from thermopower waves can help in the design of optimized hybrid composites of nanomaterials and fuels, especially designs based on the internal alignment of the materials. More generally, we believe that this work provides clues to the process of chemical to thermal to electrical energy conversion inside/outside hybrid nanostructured materials.     

Nanostructures generated from photopolymerization of poly(ethylene glycol) diacrylate templated from hexagonal lyotropic liquid crystals

The use of lyotropic liquid crystals (LLC) as a template to form periodic nanostructures in polymer materials is a promising technology. In this study, cross‐linked poly(ethylene glycol) diacrylate nanostructured materials were prepared by photopolymerization in LLC hexagonal phases. Polarized light microscopy and small‐angle powder X‐ray diffraction were used to understand the original LLC order retention on photopolymerization, and scanning electron microscope was used to investigate the morphology under different purifying solvents and drying conditions. A Quantachrome Autosorb 1 system was used to study the pore size distribution of samples. It was found that the LLC hexagonal structure was retained to a great extent after photopolymerization. The formation of nanostructures was affected by purifying solvent and drying condition. The nanostructure synthesized from LLC with favorably aligned nanopores will find increasing applications in gas and water filtration, biology, and health science. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Multi‐Component Self‐Assembly of Proteins and Inorganic Particles: From Discrete Structures to Biomimetic Materials

Due to their defined structure, proteins are suitable building blocks for the bottom‐up construction of multi‐component materials. Especially protein containers, with their inherent cavity, can be used to encapsulate synthetic components such as inorganic nanoparticles. This way, multi‐component discrete structures can be assembled. With recent advances in computational protein design, novel protein containers were successfully created, with a high potential for application in biomedicine and materials research. Moreover, engineered protein containers offer a unique building block for the self‐assembly of three‐dimensional materials. They combine the molecular precision of proteins with nanoscale dimensions. Designed interactions lead to novel protein scaffolds. In addition, nanoparticles encapsulated inside the container cavity introduce orthogonal functionality, important for the realization of nanostructured biomimetic materials with emergent properties.     

Fabrication of Large Area Periodic Nanostructures Using Nanosphere Photolithography

Large area periodic nanostructures exhibit unique optical and electronic properties and have found many applications, such as photonic band-gap materials, high dense data storage, and photonic devices. We have developed a maskless photolithography method—Nanosphere Photolithography (NSP)—to produce a large area of uniform nanopatterns in the photoresist utilizing the silica micro-spheres to focus UV light. Here, we will extend the idea to fabricate metallic nanostructures using the NSP method. We produced large areas of periodic uniform nanohole array perforated in different metallic films, such as gold and aluminum. The diameters of these nanoholes are much smaller than the wavelength of UV light used and they are very uniformly distributed. The method introduced here inherently has both the advantages of photolithography and self-assembled methods. Besides, it also generates very uniform repetitive nanopatterns because the focused beam waist is almost unchanged with different sphere sizes.     

Morphology-controlled synthesis and field-emission properties of patterned SnO2 nanostructures with different morphologies

Tin oxide nanostructured arrays with different morphologies were grown on stainless-steel mesh substrates by a simple thermal evaporation process. It was found that the SnO₂ nanostructures could be easily changed from nanobelts to nanocones, nanoneedles, micro-rods, ultra-long nanowires, and slim nanorods by controlling the parameters of growth temperature and N₂/O₂ flow. A model combining vapor-liquid-solid (VLS)-base growth and vapor-solid (VS)-tip growth was proposed to explain the growth of SnO₂ nanostructures with manifold morphologies. Field-emission (FE) studies revealed that the morphologies of these patterned SnO₂ nanostructures had considerable effects on the FE properties. Among these nanostructures, ultra-long nanowire arrays had the lowest turn-on field (~0.47 V/um) and the highest field enhancement factor (~8848). More importantly, the ultra-long nanowire emitters showed excellent FE stability with fluctuations within 2.7%. The enhanced FE properties may be attributed to synergic effects arising from the aligned structures of the ultra-long nanowire emitters, their smaller areal density and their highest aspect ratio (~12000).     

生物分子模板法制备不同形貌硫化铅纳米材料

通过生物分子模板法制备了不同形貌的硫化铅纳米材料,对比实验发现半胱氨酸的添加量及铅-半胱氨酸前驱体的形貌对最终产物的生成有很大影响.通过控制半胱氨酸的加入量,制备了树枝状、分级结构及多臂硫化铅纳米材料,这些形貌的成功制备将对功能性纳米器件的组装有重要意义.所采用的生物分子模板法具有简单、环境友好等优势,有利于其它半导体纳米材料的大规模制备.