Search

In aromatic systems with large π-conjugated structures, armchair and zigzag configurations can affect each material’s electronic properties, determining their performance and generating certain quantum effects. Here, we explore the intrinsic effect of armchair and zigzag pathways on charge transport through single hexabenzocoronene molecules. Theoretical calculations and systematic experimental results from static carbon-based single-molecule junctions and dynamic scanning tunneling microscope break junctions show that charge carriers are preferentially transported along the hexabenzocoronene armchair pathway, and thus, the corresponding current through this pathway is approximately one order of magnitude higher than that through the zigzag pathway. In addition, the molecule with the zigzag pathway has a smaller energy gap. In combination with its lower off-state conductance, it shows a better field-effect performance because of its higher on-off ratio in electrical measurements. This study on charge transport pathways offers a useful perspective for understanding the electronic properties of π-conjugated systems and realizing high-performance molecular nanocircuits toward practical applications.

Here, six phenanthrene (the smallest arm-chair graphene nanoribbon) derivatives with dithiomethyl substitutions at different positions as the anchoring groups were synthesized. Scanning tunneling microscopy break junction technique was used to measure their single molecule conductances between gold electrodes, which showed a difference as much as 20-fold in the range of ∼10

Amides are essential in the chemistry of life. Detecting the chemical bond states within amides could unravel the nature of amide stabilization and planarity, which is critical to the structure and reactivity of such molecules. Yet, so far, no work has been reported to detect or measure the bond changes at the single-molecule level within amides. Here, we show that a transition between single and double bonds between N and C atoms in an amide can be monitored in real time in a nanogap between gold electrodes via the generation of distinctive conductance features. Density functional theory simulations show that the switching between amide isomers proceeds via a proton transfer process facilitated by a water molecule bridge, and the resulting molecular junctions display bimodal conductance states with a difference as much as nine times.

Lithium-sulfur (Li-S) batteries are severely hindered by the low sulfur utilization and short cycling life, especially at high rates. One of the effective solutions to address these problems is to improve the sulfiphilicity of lithium polysulfides (LiPSs) and the lithiophilicity of the lithium anode. However, it is a great challenge to simultaneously optimize both aspects. Herein, by incorporating the merits of strong absorbability and high conductivity of SnS with good catalytic capability of ZnS, a ZnS-SnS heterojunction coated with a polydopamine-derived N-doped carbon shell (denoted as ZnS-SnS@NC) with uniform cubic morphology was obtained and compared with the ZnS-SnS2@NC heterostructure and its single-component counterparts (SnS@NC and SnS2@NC). Theoretical calculations, ex situ XANES, and in situ Raman spectrum were utilized to elucidate rapid anchoring-diffusion-transformation of LiPSs, inhibition of the shuttling effect, and improvement of the sulfur electrochemistry of bimetal ZnS-SnS heterostructure at the molecular level. When applied as a modification layer coated on the separator, the ZnS-SnS@NC-based cell with optimized lithiophilicity and sulfiphilicity enables desirable sulfur electrochemistry, including high reversibility of 1149 mAh g-1 for 300 cycles at 0.2 C, high rate performance of 661 mAh g-1 at 10 C, and long cycle life with a low fading rate of 0.0126% each cycle after 2000 cycles at 4 C. Furthermore, a favorable areal capacity of 8.27 mAh cm-2 is maintained under high sulfur mass loading of 10.3 mg cm-2. This work furnishes a feasible scheme to the rational design of bimetal sulfides heterostructures and boosts the development of other electrochemical applications.

Despite the rapid development of fluorescence detectors over the past decade, it still remains a considerable challenge to exploit a highly stable, sensitive, and selective fluorescence platform for molecular recognition. In this study, we report a stable carbazole-based sp2 carbon fluorescence covalent organic framework (COF) nanosheet, termed JUC-557-nanosheet. Owing to the synergistic effect of AIE- and ACQ-based chromophores in JUC-557-nanosheet, this architecture shows high absolute quantum yields (up to 23.0%) in solid state and the dispersed in various solvents and excellent sensing performance toward specific analytes, such as iodine (Ka: 2.10  105 M-1 and LOD: 302 ppb), 2,4,6-trinitrotoluene (Ka: 4.38  105 M-1 and LOD: 129 ppb), and especially nitrobenzene (Ka: 6.18  106 M-1 and LOD: 5 ppb), which is superior to those of fluorescence detection materials reported so far, including porous materials, small molecule probes and inorganics. Furthermore, its fluorescence quenching mechanism has been demonstrated to be a synergistic effect of static quenching and energy transfer quenching by a combined theoretical and experimental study, including time-resolved photoluminescence measurements, UV-vis absorption spectroscopy, and density functional theory calculations. As a chemically stable material, JUC-557-nanosheet preserves strong luminescence and sensitive recognition even under harsh conditions (such as strong acid with pH = 1 or strong base with pH = 14), and allows trace detection of various analytes via a handheld UV lamp. Therefore, these findings pave the way for developing stable ultrathin COF nanomaterials for highly sensitive and selective molecular detection.

The low conductivity, shuttling phenomenon, and sluggish transformation of intermediate lithium polysulfides (LiPSs) constitute primary obstacles for the practical application of lithium–sulfur (Li–S) batteries. Ultrathin double-shell nanotubes of titanium oxide with oxygen-vacancy@nitrogen-doped carbon (denoted as OV-TiO2−x@NC) as the sulfur host were designed. As demonstrated by experimental and computational results, an ultrathin TiO2−x shell featuring a small aspect ratio can not only provide rapid charge transfer but also shorten the diffusion pathway of lithium ions. Furthermore, the special double-shell nanostructure with the large surface area can accommodate high number of sulfur species, provide effective channels for the electrolyte penetration, supply adequate buffer space for alleviating the volume expansion of sulfur upon repeated cycling, and provide both physical and chemical adsorption to efficiently capture LiPSs. The OV-TiO2−x inner shell with a small aspect ratio is compactly packed and tightly adhered to the carbon layer, which can effectively anchor LiPSs with strong chemical affinity and prevent their diffusion from the inner to the outside layer. More importantly, the introduction of oxygen-vacancies can enhance the conductivity of electrode, restrict the loss of LiPSs into the electrolyte, strengthen electrocatalytic activity, and accelerate LiPSs conversion. Endowed with these properties, the OV-TiO2−x@NC/S electrode enables excellent electrochemical performance, including long cycle stability of 531 mA h g−1 for 3000 cycles at 5C with decay rate of only 0.0123%, excellent rate capability of 675 mA h g−1 at 8C and high areal capacity of 8.01 mA h cm−2 with sulfur mass loading of 9.5 mg cm−2 under low electrolyte/sulfur (E/S = 5). This work provides perspective on altering the electronic states of OV–metal oxides toward high energy density Li–S batteries and promotes the progress of catalysis or energy storage systems.

Dry reforming of methane (DRM) over Ni-based catalysts is a promising method to convert greenhouse gases CH4 and CO2 into valuable synthesis gas. However, the major drawback of DRM over Ni-based catalysts is its deactivation due to metal sintering and coke formation. Herein, Ni catalysts confined between boron nitride (BN)–nanoceria (NC) interfaces have been originally developed and demonstrated as efficient and stable DRM catalysts, which exhibit high activity and high resistance towards carbon deposition. The stronger interaction between nickel and BN–nanoceria interfaces led to higher concentration of Ce3+ species, which promotes adsorption and activation of CO2 and thus facilitates the fast formation of –OH species. The active –OH species is crucial to prevent coke formation and improve the stability of Ni catalysts. This work demonstrates that restriction of metal nanoparticles within a nano-interface through the confinement effect is a successful strategy to develop coke-resistant catalysts.

International audience; The aim of molecular electronics is to miniaturize active electronic devices and ultimately construct single-molecule nanocircuits using molecules with diverse structures featuring various functions, which is extremely challenging. Here, we realize a gate-controlled rectifying function (the on/off ratio reaches ∼60) and a high-performance field effect (maximum on/off ratio >100) simultaneously in an initially symmetric single-molecule photoswitch comprising a dinuclear ruthenium-diarylethene (Ru-DAE) complex sandwiched covalently between graphene electrodes. Both experimental and theoretical results consistently demonstrate that the initially degenerated frontier molecular orbitals localized at each Ru fragment in the open-ring Ru-DAE molecule can be tuned separately and shift asymmetrically under gate electric fields. This symmetric orbital shifting (AOS) lifts the degeneracy and breaks the molecular symmetry, which is not only essential to achieve a diode-like behavior with tunable rectification ratio and controlled polarity, but also enhances the field-effect on/off ratio at the rectification direction. In addition, this gate-controlled symmetry-breaking effect can be switched on/off by isomerizing the DAE unit between its open-ring and closed-ring forms with light stimulus. This new scheme offers a general and efficient strategy to build high-performance multifunctional molecular nanocircuits.

Divergent synthesis of four contorted aromatics containing pentagons, a heptagon, and/or an azulene from the same difluorenyl pentacenediene precursor were realized in one step. The subtle differences in molecular structure were confirmed by X-ray crystallography. The mechanisms for the control of different products, which involve a ring-expansion rearrangement, Scholl reactions, and/or Mallory cyclization were proposed on the basis of control experiments and DFT calculations. Such development adds good structure versatility and materials accessibility to the study of contorted aromatics.

The single-molecule conductance of silanes is suppressed due to destructive quantum interference in conformations with cisoid dihedral angles along the molecular backbone. Yet, despite the structural similarity, σ-interference effects have not been observed in alkanes. Here we report that the methyl substituents used in silanes are a prerequisite for σ-interference in these systems. Through density functional theory calculations, we find that the destructive interference is not evident to the same extent in nonmethylated silanes. We find the same is true in alkanes as the transmission is significantly suppressed in permethylated cyclic and bicyclic alkanes. Using scanning tunneling microscope break-junction method we determine the single-molecule conductance of functionalized cyclohexane and bicyclo[2.2.2]octane that are found to be higher than that of equivalent permethylated silanes. Rather than the difference between carbon and silicon atoms in the molecular backbones, our calculations reveal that it is primarily the difference between hydrogen and methyl substituents that result in the different electron transport properties of nonmethylated alkanes and permethylated silanes. Chemical substituents play an important role in determining the single-molecule conductance of saturated molecules, and this must be considered when we improve and expand the chemical design of insulating organic molecules.

The development of highly-sensitive recognition of hazardous chemicals, such as volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs), is of significant importance because of their widespread social concerns related to environment and human health. Here, we report a three-dimensional (3D) covalent organic framework (COF, termed JUC-555) bearing tetraphenylethylene (TPE) side chains as an aggregation-induced emission (AIE) fluorescence probe for sensitive molecular recognition. Due to the rotational restriction of TPE rotors in highly interpenetrated framework after inclusion of dimethylformamide (DMF), JUC-555 shows impressive AIE-based strong fluorescence. Meanwhile, owing to the large pore size (11.4 Å) and suitable intermolecular distance of aligned TPE (7.2 Å) in JUC-555, the obtained material demonstrates an excellent performance in the molecular recognition of hazardous chemicals, e.g., nitroaromatic explosives, PAHs, and even thiophene compounds, via a fluorescent quenching mechanism. The quenching constant (KSV) is two orders of magnitude better than those of other fluorescence-based porous materials reported to date. This research thus opens 3D functionalized COFs as a promising identification tool for environmentally hazardous substances.

N-doping of graphdiyne with atomic precision is very important for the study of heteroatom doping effect and the structure-properties relationships of graphdiyne. Here we report the bottom-up synthesis and characterizations of high-quality pyrazinoquinoxaline-based graphdiyne (PQ-GDY) film. First-principle studies of the layered structure were performed to examine the stacking mode, lithium binding affinity, and bulk lithium storage capacity. Three-stage insertion of 14 lithium atoms with binding affinities in the order of pyrazine nitrogen > diyne carbon > central aromatic ring were confirmed by both lithium-ion half-cell measurements and DFT calculations. More than half of the lithium atoms preferentially bind to pyrazine nitrogen, and a reversible capacity of 570.0 mA h g-1 at a current density of 200 mA g-1 after 800 cycles was achieved. Such a high capacity utilization rate of 97.2% provides a good case study of N-doped GDY with atomic precision.

This study explores a new mode of contortion in perylene diimides where the molecule is bent, like a bow, along its long axis. These bowed PDIs were synthesized through a facile fourfold Suzuki macrocyclization with aromatic linkers and a tetraborylated perylene diimide that introduces strain and results in a bowed structure. By altering the strings of the bow, the degree of bending can be controlled from flat to highly bent. Through spectroscopy and quantum chemical calculations, it is demonstrated that the energy of the lowest unoccupied orbital can be controlled by the degree of bending in the structures and that the energy of the highest occupied orbital can be controlled to a large extent by the constitution of the aromatic linkers. The important finding is that the bowing results not only in red-shifted absorptions but also more facile reductions.

Linear silanes are efficient molecular wires due to strong σ-conjugation in the transoid conformation; however, the structure-function relationship for the conformational dependence of the single-molecule conductance of silanes remains untested. Here we report the syntheses, electrical measurements, and theoretical characterization of four series of functionalized cyclic and bicyclic silanes including a cyclotetrasilane, a cyclopentasilane, a bicyclo[2.2.1]heptasilane, and a bicyclo[2.2.2]octasilane, which are all extended by linear silicon linkers of varying length. We find an unusual variation of the single-molecule conductance among the four series at each linker length. We determine the relative conductance of the (bi)cyclic silicon structures by using the common length dependence of the four series rather than comparing the conductance at a single length. In contrast with the cyclic π-conjugated molecules, the conductance of σ-conjugated (bi)cyclic silanes is dominated by a single path through the molecule and is controlled by the dihedral angles along this path. This strong sensitivity to molecular conformation dictates the single-molecule conductance of σ-conjugated silanes and allows for systematic control of the conductance through molecular design.

Upon oxidation, a graphyne-like porous carbon-rich network (GYLPC), which is a two-dimensional carbon material consisting of sp- and sp2-hybridized carbon atoms synthesized via alkyne metathesis reactions, yielded GYLPC oxide (GYLPCO). The highly electron-rich conjugated structure provides this new material GYLPC and its oxide GYLPCO with low reduction potentials, which are found to be able to serve as reductants and stabilizers for electroless deposition of well-dispersed Pd metal nanoparticles. The unique Pd/GYLPCO showed extremely high catalytic activity for a broad scope of nitrobenzene reduction reactions with short reaction time and good yields, even in aqueous media under aerobic conditions. We expect that our approach will further boost research on the design and application of graphyne-like functional materials for catalysis.

The tunnelling of electrons through molecules (and through any nanoscale insulating and dielectric material 1 ) shows exponential attenuation with increasing length 2 , a length dependence that is reflected in the ability of the electrons to carry an electrical current. It was recently demonstrated3-5 that coherent tunnelling through a molecular junction can also be suppressed by destructive quantum interference 6 , a mechanism that is not length-dependent. For the carbon-based molecules studied previously, cancelling all transmission channels would involve the suppression of contributions to the current from both the π-orbital and σ-orbital systems. Previous reports of destructive interference have demonstrated a decrease in transmission only through the π-channel. Here we report a saturated silicon-based molecule with a functionalized bicyclo[2.2.2]octasilane moiety that exhibits destructive quantum interference in its σ-system. Although molecular silicon typically forms conducting wires 7 , we use a combination of conductance measurements and ab initio calculations to show that destructive σ-interference, achieved here by locking the silicon-silicon bonds into eclipsed conformations within a bicyclic molecular framework, can yield extremely insulating molecules less than a nanometre in length. Our molecules also exhibit an unusually high thermopower (0.97 millivolts per kelvin), which is a further experimental signature of the suppression of all tunnelling paths by destructive interference: calculations indicate that the central bicyclo[2.2.2]octasilane unit is rendered less conductive than the empty space it occupies. The molecular design presented here provides a proof-of-concept for a quantum-interference-based approach to single-molecule insulators.

Li metal anode (LMA) for practical Li-metal batteries suffers from safety hazards and capacity deterioration caused by its high reactivity and infinite volume change. Herein, a stable LMA with highly uniform surface potential distribution was demonstrated by coating Li with a negatively charged artificial solid electrolyte interphase (ASEI), which is formed by spontaneous in-situ polymerization of 2,3,7,8-tetrakis((trimethylsilyl)ethynyl)pyrazino[2,3-g]quinoxaline-5,10-dione (PPQ) at room temperature. As an ion-transport regulator, such an ASEI with negatively charged moieties provides preferential Li-ion transport with high Li-ion transference number (tLi+ = 0.74). As a robust artificial layer, the PPQ-stabilized Li (PPQ-Li) maintains high mechanical strength (Young’s modulus of 7.39 GPa) after being immersed in electrolyte, which readily suppresses formation of hazardous Li dendrites and diminishes parasitic reactions on LMA, leading to dendrite-free morphology after long-term Li stripping-plating tests. Such a multi-functional interphase could potentially promote more tailorable coating designs for practically durable LMA.

Singlet fission, the generation of two triplet excited states from the absorption of a single photon, may potentially increase solar energy conversion efficiency. A major roadblock in realizing this potential is the limited number of molecules available with high singlet fission yields and sufficient chemical stability. Here, we demonstrate a strategy for developing singlet fission materials in which we start with a stable molecular platform and use strain to tune the singlet and triplet energies. Using perylene diimide as a model system, we tune the singlet fission energetics from endoergic to exoergic or iso-energetic by straining the molecular backbone. The result is an increase in the singlet fission rate by 2 orders of magnitude. This demonstration opens a door to greatly expanding the molecular toolbox for singlet fission.

This Account describes a body of research on the design, synthesis, and application of a new class of electronic materials made from conjugated macrocycles. Our macrocyclic design takes into consideration the useful attributes of fullerenes and what properties make fullerenes efficient n-type materials. We identified four electronic and structural elements: (1) a three-dimensional shape; (2) a conjugated and delocalized π-space; (3) the presence of an interior and exterior to the π-surface; and (4) low-energy unoccupied molecular orbitals allowing them to accept electrons. The macrocyclic design incorporates some of these properties, including a three-dimensional shape, an interior/exterior to the π-surface, and low-lying LUMOs maintaining the n-type semiconducting behavior, yet we also install synthetic flexibility in our approach in order to tune the properties further. Each of the macrocycles comprises perylenediimide cores wound together with linkers. The perylenediimide building block endows each macrocycle with the ability to accept electrons, while the synthetic flexibility to install different linkers allows us to create macrocycles with different electronic properties and sizes. We have created three macrocycles that all absorb well into the visible range of the solar spectrum and possess different shapes and sizes. We then use these materials in an array of applications that take advantage of their ability to function as n-type semiconductors, absorb in the visible range of the solar spectrum, and possess intramolecular cavities. This Account will discuss our progress in incorporating these new macrocycles in organic solar cells, organic photodetectors, organic field effect transistors, and sensors. The macrocycles outperform acyclic controls in organic solar cells. We find the more rigid macrocyclic structure results in less intrinsic charges and lower dark current in organic photodetectors. Our macrocyclic-based photodetector has the highest detectivity of non-fullerene acceptors. The macrocycles also function as sensors and are able to recognize nuanced differences in analytes. Perylenediimide-based fused oligomers are efficient materials in both organic solar cells and field effect transistors. We will use the oligomers to construct macrocycles for use in solar energy conversion. In addition, we will incorporate different electron-rich linkers in our cycles in an attempt to engineer the HOMO/LUMO gap further. Looking further into the future, we envision opportunities in applying these conjugated macrocycles as electronic host/guest materials, as concatenated electronic materials by threading the macrocycles with electroactive oligomers, and as a locus for catalysis that is driven by light and electric fields.

A new method for the effective synthesis of coronene tetracarboxydiimide (CDI) was developed by utilizing inexpensive and nontoxic potassium vinyltrifluoroborate. Controllable brominations of CDI were accomplished to yield CDI mono-, di-, tri-, and tetra-bromides, which could be used as synthon and functionalized by aromatic nucleophilic substitution and the Sonogashira coupling reaction.

Here we examine the impact of ring conformation on the charge transport characteristics of cyclic pentasilane structures bound to gold electrodes in single molecule junctions. We investigate the conductance properties of alkylated cyclopentasilane cis and trans stereoisomers substituted in the 1,3-position with methylthiomethyl electrode binding groups using both the scanning tunneling microscope-based break junction technique and density functional theory based ab initio calculations. In contrast with the linear ones, these cyclic silanes yield lower conductance values; calculations reveal that the constrained dihedral geometries occurring within the ring are suboptimal for σ-orbital delocalization, and therefore, conductance. Theoretical calculations reproduce the measured conductance trends for both cis and trans isomers and find several distinct conformations that are likely to form stable molecular junctions at room temperature. Due to the weakened σ-conjugation in the molecule, through-space interactions are found to contribute significantly to the conductance. This manuscript details the vast conformational flexibility in cyclopentasilanes and the tremendous impact it has on controlling conductance.

We present here a new design motif for strained, conjugated macrocycles that incorporates two different aromatics into the cycle with an -A-B-A-B- pattern. In this study, we demonstrate the concept by alternating electron donors and acceptors in a conjugated cycle. The donor is a bithiophene, and the acceptor is a perylene diimide derivative. The macrocycle formed has a persistent elliptiform cavity that is lined with the sulfur atoms of the thiophenes and the π-faces of the perylene diimide. Due to the linkage of the perylene diimide subunits, the macrocycles exist in both chiral and achiral forms. We separate the three stereoisomers using chiral high-performance liquid chromatography and study their interconversion. The mechanism for interconversion involves an "intramolecular somersault" in which one of the PDIs rotates around its transverse axis, thereby moving one of its diimide heads through the plane of the cavity. These unusual macrocycles are black in color with an absorption spectrum that spans the visible range. Density functional theory calculations reveal a photoinduced electron transfer from the bithiophene to the perylene diimide.

CONSPECTUS: This Account describes a body of research in the design, synthesis, and assembly of molecular materials made from strained polycyclic aromatic molecules. The strain in the molecular subunits severely distorts the aromatic molecules away from planarity. We coined the term "contorted aromatics" to describe this class of molecules. Using these molecules, we demonstrate that the curved pi-surfaces are useful as subunits to make self-assembled electronic materials. We have created and continue to study two broad classes of these "contorted aromatics": discs and ribbons. The figure that accompanies this conspectus displays the three-dimensional surfaces of a selection of these "contorted aromatics". The disc-shaped contorted molecules have well-defined conformations that create concave pi-surfaces. When these disc-shaped molecules are substituted with hydrocarbon side chains, they self-assemble into columnar superstructures. Depending on the hydrocarbon substitution, they form either liquid crystalline films or macroscopic cables. In both cases, the columnar structures are photoconductive and form p-type, hole- transporting materials in field effect transistor devices. This columnar motif is robust, allowing us to form monolayers of these columns attached to the surface of dielectrics such as silicon oxide. We use ultrathin point contacts made from individual single-walled carbon nanotubes that are separated by a few nanometers to probe the electronic properties of short stacks of a few contorted discs. We find that these materials have high mobility and can sense electron-deficient aromatic molecules. The concave surfaces of these disc-shaped contorted molecules form ideal receptors for the molecular recognition and assembly with spherical molecules such as fullerenes. These interfaces resemble ball-and-socket joints, where the fullerene nests itself in the concave surface of the contorted disc. The tightness of the binding between the two partners can be increased by creating more hemispherically shaped contorted molecules. Given the electronic structure of these contorted discs and the fullerenes, this junction is a molecular version of a p-n junction. These ball-and-socket interfaces are ideal for photoinduced charge separation. Photovoltaic devices containing these molecular recognition elements demonstrate approximately two orders of magnitude increase in charge separation. The ribbon-shaped, contorted molecules can be conceptualized as ultranarrow pieces of graphene. The contortion causes them to wind into helical ribbons. These ribbons can be formed into the active layer of field effect transistors. We substitute the ribbons with di-imides and therefore are able to transport electrons. Furthermore, these materials absorb light strongly and have ideal energetic alignment of their orbitals with conventional p-type electronic polymers. In solar cells, these contorted ribbons with commercial donor polymers have record efficiencies for non-fullerene-based solar cells. An area of interest for future exploration is the merger of these highly efficient contorted ribbons with the well-defined interfaces of the ball-and-socket materials.

This manuscript describes a synthesis of nanocrystalline TiOF2 film. The nanocrystalline TiOF2 becomes chemically attached to the surface of the glass slide. These films are robust and can be recycled as photocatalysts for the degradation of organic dyes and solvents. These films also have significant antibacterial properties upon irradiation.

Here, we compare analogous cyclic and acyclic π-conjugated molecules as n-type electronic materials and find that the cyclic molecules have numerous benefits in organic photovoltaics. This is the first report of such a direct comparison. We designed two conjugated cycles for this study. Each comprises four subunits: one combines four electron-accepting, redox-active, diphenyl-perylenediimide subunits, and the other alternates two electron-donating bithiophene units with two diphenyl-perylenediimide units. We compare the macrocycles to acyclic versions of these molecules and find that, relative to the acyclic analogs, the conjugated macrocycles have bathochromically shifted UV-vis absorbances and are more easily reduced. In blended films, macrocycle-based devices show higher electron mobility and good morphology. All of these factors contribute to the more than doubling of the power conversion efficiency observed in organic photovoltaic devices with these macrocycles as the n-type, electron transporting material. This study highlights the importance of geometric design in creating new molecular semiconductors. The ease with which we can design and tune the electronic properties of these cyclic structures charts a clear path to creating a new family of cyclic, conjugated molecules as electron transporting materials in optoelectronic and electronic devices.

Described here is a new and highly general strategy for multiple-template (multitemplate) patterning. This process is significant because it allows us to create various unusual shapes such as solid spheres, yolk-shell spheres, flowerlike particles, and structured nanocomponents. Alcoholysis of the metal-organic precursors with mixtures of glycerol and various amounts of ethanol followed by calcination yields oxides. The glycerol plays the dual role of hierarchically assembling the metal-organic composites and stabilizing the structures during the subsequent conversions. Furthermore, we demonstrate for the first time that these metal-organic composites can be converted into oxides, nitrides, and highly graphitized carbon nanostructures. We show that these yolk-shell structures display superior photocatalytic activity and electrochemical properties.

The pick-up-stick transistor concept is demonstrated using materials that are both air-stable and fully solution processable. In this paper, the thin film transistor (TFT) semiconductor is a bilayer structure with an array of carbon nanotubes (CNTs) as an underlayer and an alkyl-substituted hexabenzocoronene (HBC) overcoat. Electrical current flowing through the structure favors the low resistance CNTs, and therefore, the effective channel length, transconductance, and charge carrier mobility are modulated by the CNT density. With this structure, we measure a field effect mobility of 0.1 cm2/Vs which represents a factor of 6 improvement over that of HBC without a CNT underlayer. All fabrication is carried out in a bright, air-filled environment.

We describe the use of benzyl alcohols in a solvothermal/alcoholysis reaction to form nanocrystalline sheets of anatase titania. By tuning the reaction conditions, we adjust the size of the nanosheets. The type and density of benzyl groups that decorate the basal plane of the titania sheets control the self-assembly into layered structures. These layered materials can be grown from solid substrates to create iridescent thin films that reflect specific wavelengths of visible light.

We demonstrate a new, simple, inexpensive process and systemic control over CdS nanowires using sulfur powders and organic diamines without any catalysts, surfactants, and templates under atmospheric benchtop conditions. By changing the kinds of amines and reaction temperatures can result in control of the shape and size of the nanocrystals, which are moderately monodispered with unique forms.

A new self-assembly system between a PPV derivative and an organofullerene through a three-point hydrogen-bonding interaction was prepared. The formation of hydrogen bonding was confirmed by 1H NMR studies in CDCl3. Fluorescence quenching experiments indicated that the fluorescence of U-PPV was greatly quenched by DAP-C60 (KSV = 5.8 × 104 M-1).

The electrochemical behaviors of a novel class C60 covalently linked PPV derivatives (i.e., PPV-1-C60 and PPV-2-C60) in thin solid films as well as in solutions are reported. The first cathodic peak potentials of PPV-1-C60 and PPV-2-C60 have positive shifts by 30 and 50 mV, respectively, compared to pristine C60 in formal cyclic voltammetry (CV). Simultaneous CV and piezoelectric microgravimetry of the drop-coated thin solid films of PPV-1-C60 and PPV-2-C60 in acetonitrile solutions of TBA+ counteractions are strongly influenced by the structure of the polymer-C60, including the length of the chain macromolecule and the steric hindrance effect. In addition, the atomic force microscopy (AFM) images of PPV-1-C60 and PPV-2-C60 films deposited on Au/quartz electrode both exhibit even distribution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2737–2741, 2002

A series of new poly(phenylenevinylene) (PPV) derivatives covelently linked with fullerenes (C 60 ) were synthesized and characterized. Copolymers containing different percentage of C 60 were obtained by controlling the percentage of azido groups in the initial feed ratio. The absorption spectra of copolymer (PPV-C 60 ) showed two peaks in the regions of 410 and 330 nm. The former peak was interpreted as being the π-π* interband excitation of copolymer PPV followed by electron transfer to C 60 , while the latter was attributed to the optical excitation of the C 60 moiety. Cyclic voltammetry (CV) analysis showed the presence of interaction between the PPV unit and fullurene moiety in the ground state. Fluorescence spectra of the copolymers indicated charge transfer from the π* band of the photoexcited PPV of the copolymer to the C 60 .

A novel PPV-[C60] dyad which was partly soluble in common organic solvent was synthesized via the cycloaddition reaction of azide group with [C60]fullerene. Copolymer PPV-[C60] was isolated in up to 70% yields with molecular weights ranging up to 3615 relative to polystyrene standards. Cyclic voltammeter (CV) analysis for the copolymers showed three reversible waves. UV–VIS and fluorescence spectra of the copolymer were also studied.

New sensitizing dye–semiconductor system comprised of 3,4,9,10-perylene tetracarboxylic acid (PTCA) or perylene 3,4-dicarboxylic-9,10-( n -butylamine) carboximide (PNDCA) on titanium dioxide (TiO 2 ) had been prepared and characterized. Good energy conversion efficiency was obtained. The film of PTCA on TiO 2 yielded an incident photo-to-current efficiency (IPCE) of approximately 40% in the wavelength region of 440 to 530 nm, while that for PNDCA was approximately 14% at the wavelength region from 460 to 510 nm. Further studies concentrated on the doping of this system with bromine (Br 2 ). The results indicated that the sensitizing wavelength region was red shifted, which was advantageous for solar light harvesting. Furthermore, the doped films gave lower quantum conversion efficiency than the non-doped films.

[structure: see text] Novel self-assembly systems of uracil derivatives with organofullerene by a three-point hydrogen-bonding interaction were designed and established. The formation of hydrogen bonding was established by 1H NMR studies in CDCl3.

New C 60 covalently linked PPV derivatives containing carbazole moiety poly{(2,5-di-pentoxyl-phenylene)-1,4-diylvinylene-3,6-[9-(1-azafulleroid-propyl)carbazolenevinylene]} (PPV-AFCAR) were synthesized and characterized. The polymers containing different percentage of C 60 were obtained through the percentage of azido unit being controlled by the initial feed ratio. Cyclic voltametric analysis showed that the electronic characteristic remained while it covalently attached to polymer by the cycloaddition reaction. The fluorescences of PPV moieties were strongly quenched due to the presence of fullerene.

New C60-based dyads containing carbazole and benzothiazole moieties were synthesized. Two synthetic routes were studied.

We report an efficiency of 6.1% for a solution-processed non-fullerene solar cell using a helical perylene diimide (PDI) dimer as the electron acceptor. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor–acceptor interfaces, indicating that charge carriers are created from photogenerated excitons in both the electron donor and acceptor phases. Light-intensity-dependent current–voltage measurements suggested different recombination rates under short-circuit and open-circuit conditions.

We describe the design and synthesis of a new graphene ribbon architecture that consists of perylenediimide (PDI) subunits fused together by ethylene bridges. We created a prototype series of oligomers consisting of the dimer, trimer, and tetramer. The steric congestion at the fusion point between the PDI units creates helical junctions, and longer oligomers form helical ribbons. Thin films of these oligomers form the active layer in n-type field effect transistors. UV–vis spectroscopy reveals the emergence of an intense long-wavelength transition in the tetramer. From DFT calculations, we find that the HOMO–2 to LUMO transition is isoenergetic with the HOMO to LUMO transition in the tetramer. We probe these transitions directly using femtosecond transient absorption spectroscopy. The HOMO–2 to LUMO transition electronically connects the PDI subunits with the ethylene bridges, and its energy depends on the length of the oligomer.

Low-temperature scanning tunneling microscopy measurements and first-principles calculations are employed to characterize edge structures observed for graphene nanoislands grown on the Co(0001) surface. Images of these nanostructures reveal straight well-ordered edges with zigzag orientation, which are characterized by a distinct peak at low bias in tunneling spectra. Density functional theory based calculations are used to discriminate between candidate edge structures. Several zigzag-oriented edge structures have lower formation energy than armchair-oriented edges. Of these, the lowest formation energy configurations are a zigzag and a Klein edge structure, each with the final carbon atom over the hollow site in the Co(0001) surface. In the absence of hydrogen, the interaction with the Co(0001) substrate plays a key role in stabilizing these edge structures and determines their local conformation and electronic properties. The calculated electronic properties for the low-energy edge structures are consistent with the measured scanning tunneling images.

A novel salt-derivatived [60]fullerene covalently linking a stable nitroxide is synthesized. The nanoparticles based on the salt-derivatived [60]fullerene are formed in a facile way through self-assembly. The spectral properties of the sample are studied and the magnetic property is also primarily measured with superconducting quantum interference device.

A new salicylic acid modified [60]fulleropyrrodine (SFP) was synthesized and the assembly of SFP onto the surface of TiO 2 nanocrystalline thin film was accomplished through the moiety of salicylic acid as spacer. The film was fluorescent, and a strong photo-induced charge transfer from SFP to TiO 2 was observed with the maximum incident photon-to-current efficiency value exceeding 15% in visible region.