Nitrogen-Doped Ordered Mesoporous Graphitic Arrays with High Electrocatalytic Activity for Oxygen Reduction
Ruili Liu, Dongqing Wu, Xinliang Feng, Klaus Müllen, Angew. Chem. Int. Ed. 2010, 49, 2565-2569.
DOI: 10.1002/anie.200907289
These materials are no dopes: Nitrogen-doped ordered mesoporous graphitic arrays (NOMGAs) prepared by a metal-free procedure exhibited higher electrocatalytic activity than the commercially available Pt-C catalyst (see plot), excellent long-term stability, and resistance to crossover effects in the oxygen-reduction reaction (ORR). Graphite-like nitrogen atoms appear to be responsible for the excellent electrochemical performance in the ORR.
Triphenylene-Based Polymers for Blue Polymeric Light Emitting Diodes
Moussa Saleh, Martin Baumgarten, Alexey Mavrinskiy, Thomas Schäfer and Klaus Müllen, Macromolecules 2010, 43, 137–143.
DOI: 10.1021/ma901912t
An efficient synthesis has been developed toward a novel series of conjugated blue emitting polymers containing triphenylene as repeating unit for PLEDs. Soluble 1,2,3,4-tetraphenyltriphenylene, 2,3-bis(4-octylphenyl)-1,4-diphenyltriphenylene, 2-heptyl-1,3,4-triphenyltriphenylene, 2-decyl-3-(4-octylphenyl)-1,4-diphenyltriphenylene, and 2,3-diheptyl-1,4-diphenyltriphenylene-based co- and homopolymers have been synthesized by the palladium-catalyzed Suzuki−Miyaura and the nickel-catalyzed Yamamoto polycondensation reactions, respectively. The photophysical properties of the polymers were studied based on the different main chains and substituents. Because of the twisted phenyl rings around the triphenylene main core, π−π stacking in the polymers was prevented, resulting in almost identical photoluminescence (PL) spectra in both solutions and films. All polymers exhibited narrow emission in the range of 430−450 nm, where the human eye is most sensitive for the blue range.
Nanographene-Constructed Hollow Carbon Spheres and Their Favorable Electroactivity with Respect to Lithium Storage
Shubin Yang, Xinliang Feng, Linjie Zhi, Qian Cao, Joachim Maier, Klaus Müllen, Adv. Mater. 2010, 22, 838-842.
DOI: 10.1002/adma.200902795
Nanographene-constructed hollow carbon spheres (NGHCs) are fabricated using discotic nanographene as a building block and a silica/space/mesoporous silica sphere as a template. The resultant NGHCs exhibit uniform size and consist of dual walls. In the exterior walls of the NGHCs, nanochannels arrange perpendicularly to the surface, which is favorable for lithium ion diffusion from different orientations, while the interior graphitic solid walls can facilitate the collection and transport of electrons. The NGHCs show excellent electrochemical performance when used as anode material for lithium ion batteries.
A facile platform for realization of one-dimensional 1D hypersonic phononic crystals
N. Gomopoulos, D. Maschke, C. Y. Koh, E. L. Thomas, W. Tremel, H.-J. Butt, G. Fytas
Nano Lett. 2010, 10, 980-984.
DOI: 10.1021/nl903959r
We report experimental observation of a normal incidence phononic band gap in one-dimensional periodic (SiO2/poly(methyl methacrylate)) multilayer film at gigahertz frequencies using Brillouin spectroscopy. The band gap to midgap ratio of 0.30 occurs for elastic wave propagation along the periodicity direction, whereas for inplane propagation the system displays an effective medium behavior. The phononic properties are well captured by numerical simulations. The porosity in the silica layers presents a structural scaffold for the introduction of secondary active media for potential coupling between phonons and other excitations, such as photons and electrons.
Comparison of Hybrid Blends for Solar Cell Application
Maria C Lechmann, Dominik Koll, Daniel Kessler, Patrick Theato, Wolfgang Tremel, Jochen S Gutmann, Energies 2010, 3 (3), 301-312.
DOI: 10.3390/en3030301
In blended hybrid systems distinct micro- or nanostructured materials can be formed by phase separation. Network structures of particles or rods in a polymer matrix can be developed via self-assembly. We use this blending approach to compare active materials for application in solar cell devices. Blends were fabricated from either poly(hexylthiophene) P3HT or poly(triphenylamine) PTPA mixed with nanocrystalline TiO2 rods. In this manner, we compare two different hole conducting polymers in their performance in photovoltaic devices, while experimental conditions are kept identical. We find that the choice of solvent and photovoltaic characterization conducted in inert atmosphere is of importance for blends prepared from P3HT/TiO2 blends, but not for PTPA/TiO2 blends. Even though prepared with the same TiO2 rods, solar cells prepared from PTPA blends showed an enhanced efficiency when measured under ambient conditions. Furthermore, the PTPA/TiO2 showed higher long-term stability.
Influence of Cationic Additives on the Morphology of SnO2 Nanoparticles
A. Birkel, N. Loges, E. Mugnaioli, M. Panthöfer, U. Kolb, W. Tremel, Langmuir 2010, 26, 3590-3595.
Reaction pathways to SnO2 nanomaterials through the hydrolysis of hydrated tin tetrachloride precursors were investigated. The products were prepared solvothermally starting from hydrated tin tetrachloride and various (e.g., alkali) hydroxides. The influence of the precursor base on the final morphology of the nanomaterials was studied. X-ray powder diffraction (XRD) data indicated the formation of rutile-type SnO2. Transmission electron microscopy (TEM) studies revealed different morphologies that were formed with different precursor base cations. Data from molecular dynamics (MD) simulations provide theoretical evidence that the adsorption of the cations of the precursor base to the faces of the growing SnO2 nanocrystals is crucial for the morphology of the nanostructures.
A multiscale description of charge transport in conjugated oligomers
V. Rühle, James Kirkpatrick, Denis Andrienko, J. Chem. Phys. 2010, 132, 134103.
By relating inter- and intrachain ordering to charge dynamics a correlation between the morphology and charge mobility of neutral and doped states of a conjugated polymer, in this case polypyrrole, is established. Morphologies are generated using an all-atom force field, while charge dynamics is simulated within the framework of high temperature nonadiabatic Marcus theory. For short oligomers, charge carrier mobility is insensitive to the orientational molecular ordering and is determined by the threshold transfer integral which connects percolating clusters of molecules, forming interconnected networks. The value of this transfer integral can be estimated from the radial distribution function. We therefore find that charge mobility is mainly determined by the local molecular packing and is independent of global morphology, at least in such a noncrystalline state of a polymer.
The Impact of Polymer Regioregularity on Charge Transport and Efficiency of P3HT:PCBM Photovoltaic Devices
R. Mauer, M. Kastler, F. Laquai, Adv. Funct. Mater. 2010, 20,2085-2092
DOI: 10.1002/adfm.201000320
Charge-carrier transport in pristine P3HT and in P3HT blends with PCBM is studied by the time-of-flight technique. In highly regioregular (rr>98%) P3HT:PCBM blends the charge transport is non-dispersive with balanced mobilities, whereas lower regioregularity (rr~94%) leads to dispersive transport. The charge mobilities are unaffected by annealing and both polymers give similar device efficiencies.
Template-Based Preparation of Free-Standing Semiconducting Polymeric Nanorod Arrays on Conductive Substrates
Niko Haberkorn, Stefan A. L. Weber, Rüdiger Berger, and Patrick Theato, Appl. Mater. Interfaces 2010, 2,1573-1580.
DOI: 10.1021/am100085t
We described the synthesis and characterization of a cross-linkable siloxane-derivatized tetraphenylbenzidine (DTMS-TPD), which was used for the fabrication of semiconducting highly ordered nanorod arrays on conductive indium tin oxide or Pt-coated substrates. The stepwise process allowed fabricating of macroscopic areas of well-ordered free-standing nanorod arrays, which feature a high resistance against organic solvents, semiconducting properties and a good adhesion to the substrate. Thin films of the TPD derivate with good hole-conducting properties could be prepared by cross-linking and covalently attaching to hydroxylated substrates utilizing an initiator-free thermal curing at 160 °C. The nanorod arrays composed of cross-linked DTMS-TPD were fabricated by an anodic aluminum oxide (AAO) template approach. Furthermore, the nanorod arrays were investigated by a recently introduced method allowing to probe local conductivity on fragile structures. It revealed that more than 98% of the nanorods exhibit electrical conductance and consequently feature a good electrical contact to the substrate. The prepared nanorod arrays have the potential to find application in the fabrication of multilayered device architectures for building well-ordered bulk-heterojunction solar cells.
Mapping of Local Conductivity Variations on Fragile Nanopillar Arrays by Scanning Conductive Torsion Mode Microscopy
Stefan A. L. Weber, Niko Haberkorn, Patrick Theato, and Rüdiger Berger, Nano Letters 2010, 10, 1194–1197.
DOI: 10.1021/nl9035274
A gentle method that combines torsion mode topography imaging with conductive scanning force microscopy is presented. By applying an electrical bias voltage between tip and sample surface, changes in the local sample conductivity can be mapped. The topography and local conductivity variations on fragile free-standing nanopillar arrays were investigated. These samples were fabricated by an anodized aluminum oxide template process using a thermally cross-linked triphenylamine-derivate semicondcutor. The nanoscale characterization method is shown to be nondestructive. Individual nanopillars were clearly resolved in topography and current images that were recorded simultaneously.
Covalently Bonded Layer-by-Layer Assembly of Multifunctional Thin Films Based on Activated Esters
Jinhwa Seo, Philipp Schattling, Thomas Lang, Florian Jochum, Katja Nilles, Patrick Theato, Kookheon Char, Langmuir 2010, 26 (3), 1830-1836.
DOI: 10.1021/la902574z
We demonstrate that chemically stable, multifunctional polymer thin films can be obtained using the layer-by-layer (LbL) deposition based oil covalent bonds between adsorbing chains. The LbL films were shown to be quite stable in the extreme pH range, and free-standing films call easily be obtained by the treatment of the films with mild acidic conditions.
Synthesis of Heterotelechelic alpha,omega Dye-Functionalized Polymer by the RAFT Process and Energy Transfer between the End Groups
Peter J Roth, Mathias Haase, Thomas Basche, Patrick Theato, Rudolf Zentel, Macromolecules 2010, 43 (2), 895-902.
DOI: 10.1021/ma902391b
The synthesis of a vinyl polymer with two different fluorescent dye end groups using reversible addition-fragmentation chain transfer (RAFT) polymerization is described. Use of pentafluorophenyl (PFP) activated ester chain transfer agent (CTA) provided a polymer with an alpha end group that was reactive toward amines and a dithioester omega end group. The alpha PFP ester was amidated with Oregon Green Cadaverin. This did not harm the omega dithioester, which was subsequently aminolyzed with in excess of n-propylamine in the presence of Texas Red-2-sulfonamidoethyl methanethiosulfonate, resulting in a disulfide bond connecting the second dye to the polymer chain. Excess dyes and side products were removed by thin layer chromatography (TLC). Gel permeation chromatography (GPC) using a UV-vis detector could verify the presence of each dye on the polymer chain and the absence of free dyes. The s ynthesis of the polymer by a living radical technique and the mild complementary conjugation methods conducted after polymerization at each end group allowed to introduce complex dye residues possessing high brightness and photostability. In particular, fluorescent dyes capable of acting as donor and acceptor for electronic excitation energy transfer were chosen, Time-resolved fluorescence measurements were used to determine the time constant of energy transfer between the end groups of isolated polymer chains. Assuming a Forster-type process, an average end-to-end distance of 4.5 nm was calculated, which was in reasonable agreement with data obtained from light scattering.
Synthesis of Hetero-Telechelic alpha,omega Bio-Functionalized Polymers
Peter J Roth, Florian D Jochum, Rudolf Zentel, Patrick Theato, Biomacromolecules 2010, 11 (1), 238-244
DOI: 10.1021/bm901095j
Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to synthesize poly[diethylene glycol monomethylether methacrylate] (PDEGMA) (M-n = 6250 g/mol, PDI = 1.14) with a pentafluorophenyl (PFP) activated ester and a dithioester end group. The hormone thyroxin (T4) was quantitatively attached to the PFP activated ester alpha end group via its amino group. The omega-terminal dithioester was not harmed by this reaction and was subsequently aminolyzed in the presence of N-biotinylaminoethyl methanethiosulfonate, yielding a polymer with a thyroxin and a biotin end group with very high heterotelechelic functionality. The polymer was characterized by H-1, C-13, and F-19 NMR, UV-vis, and IR spectroscopy and gel permeation chromatography. The thyroxin transport protein prealbumin with two thyroxin binding sites and streptavidin, which has four biotin binding sites, was conjugated using the biotarget labeled polymer, resulting in the formation of a protein-polymer network, confirming the heterotelechelic nature of the polymer Polymer-protein microgel formation was observed with dynamic light scattering. To realize a directed protein assembly, prealbumin was immobilized onto a surface, exposing one of its two thyroxin binding groups and thus allowing the conjugation with the thyroxin alpha end group of the heterotelechelic polymer. The biotin omega end group of the attached polymer layer enabled the subsequent immobilization of streptavidin, yielding a defined multilayer system of two proteins connected with the synthetic polymer (efficiency of streptavidin immobilization 81% based on prealbumin). Without the polymer, no streptavidin immobilization occurred. The layer depositions were monitored by surface plasmon resonance. The synthetic approach of combining PFP activated esters with functional MTS reagents presents a powerful method for obtaining well-defined heterotelechelic (bio-) functionalized polymers.
Two Dimensional Self-Assembly of Disulfide Functionalized Bis-acylurea: a Nanosheet Template for Gold Nanoparticle Arrays
Jong-Uk Kim, Ki-Hyun Kim, Niko Haberkorn, Peter J. Roth, Jong-Chan Lee, Patrick Theato, Rudolf Zentel, Chem. Commun. 2010, 46, 5343-5345
A hierarchical nanostructure, where gold nanoparticles arrays are attached onto self-assembled organic nanosheets, were achieved by a two step route.
PS-b-PEO Block Copolymer Thin Films as Structured Reservoirs for Nanoscale Precipitation Reactions
Jannis W. Ochsmann, Sebastian Lenz, Sebastian G. J. Emmerling, Ralf S. Kappes, Sebastian K. Nett, Maria C. Lechmann, S. V. Roth, J. S. Gutmann, Journal of Polymer Science: Part B: Polymer Physics 2010, 48,1569-1573.
Thin films of PS-b-PEO block copolymers were utilized as structured reservoirs for localized nanoscale precipitation reactions. By consecutively immersing the film into solutions of thioacetamide and cadmium chloride, we were able to obtain a monolayer of cadmium sulfide nanostructures on top of the block copolymer film. AFM and grazing incidence small angle X-ray scattering revealed spherical nanostructures (d = 15 nm) corresponding to the dimensions given by the block copolymer film.
Orientation and Dynamics of ZnO Nanorod Liquid Crystals in Electric Fields
M. Zorn, M.N. Tahir, B. Bergmann, W. Tremel, C. Grigoriadis, G. Floudas, R. Zentel*, Macromol. Rapid Commun. 2010, 31,1101-1107.
ZnO nanorod polymer hybrids can be dispersed in a PS oligomer matrix to form LC phases. Application of electric field changes the orientation of the liquid crystal from planar (parallel to the substrate) to homeotropic (perpendicular) in full analogy to the switching of low molecular liquid crystals.
Optical Probes of Charge Generation and Recombination in Bulk-Heterojunction Organic Solar Cells
I.A. Howard, F. Laquai, Macromol. Chem. Phys. 2010, 211, 2063-2070.
DOI: 10.1002/macp.201000353
Recently, significant insight into the mechanisms of charge generation and recombination in interpenetrating networks of electron-rich donor polymers and electron-deficient acceptors used in bulk heterojunction organic solar cells has been gained through optical spectroscopy. In this article, we focus on the trend of using ultrafast transient absorption spectroscopy to observe structure–function relationships in order to provide valuable feedback and guidance for materials design and device engineering. Despite the progress, many research questions in this field still remain open, and we highlight areas in which experimental and theoretical work disagree or are still lacking. As examples of the unique and important insights that can be gained from optical spectroscopy, we review the influence of dielectric environment on charge transfer in donor–acceptor-systems and the influence of morphology on charge generation and recombination in the prototypic photovoltaic blend system regioregular poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester (P3HT:PCBM).
Effect of Morphology on Ultrafast Free Carrier Generation in Polythiophene:Fullerene Organic Solar Cells
I.A. Howard, R. Mauer, M. Meister, F. Laquai,
J. Am. Chem. Soc. 2010, 132, 14866-14876.
DOI: 10.1021/ja105260d
Despite significant study, the precise mechanisms that dictate the efficiency of organic photovoltaic cells, such as charge separation and recombination, are still debated. Here, we directly observe efficient ultrafast free charge generation in the absence of field in annealed poly(3-hexylthiophene):methanofullerene (P3HT:PCBM). However, we find this process is much less efficient in unannealed and amorphous regiorandom blends, explaining the superior short-circuit current and fill-factor of annealed RR-P3HT:PCBM solar cells. We use transient optical spectroscopy in the visible and near-infrared spectral region covering, but not limited to, the previously unobserved and highly relevant time scale spanning 1 to 100 ns, to directly observe both geminate and nongeminate charge recombination. We find that exciton quenching leads directly (time scale less than 100 fs) to two populations: bound charges and free charges. The former do not lead to photocurrent in a photovoltaic cell; they recombine geminately within 2 ns and are a loss channel. However, the latter can be efficiently extracted in photovoltaic cells. Therefore, we find that the probability of ultrafast free charge formation after exciton quenching directly limits solar cell efficiency. This probability is low in disordered P3HT:PCBM blends but approaches unity in annealed blends.
A High Gain and High Charge Carrier Mobility Indenofluorene-Phenanthrene Copolymer for Light Amplification and Organic Lasing
H. Kim, N. Schulte, G. Zhou, K. Müllen, F. Laquai,
Adv. Mater., 2010, 23, 894-897.
DOI: 10.1002/adma.201003797
Amplified spontaneous emission with unprecedented gain values is demonstrated from thin films of novel blue-light-emitting indenofluorene-phenanthrene copolymers. In addition to their excellent photoluminescence properties, high charge-carrier mobilities are observed, which makes these copolymers very promising for organic light amplifiers and lasers.
Effect of Nongeminate Recombination on Fill Factor in Polythiophene:Methanofullerene Organic Solar Cells
R. Mauer, I.A. Howard, F. Laquai,
J. Phys. Chem. Lett., 2010, 1, 3500-3505.
DOI: 10.1021/jz101458y
A key factor in solar cell efficiency is the dependence of the photocurrent on applied bias. With respect to organic solar cells, it is often suggested that this factor is governed by the field dependence of charge-transfer state separation. Here, we demonstrate that this is not the case in benchmark polythiophene/methanofullerene solar cells. By examining the temperature and light intensity dependence of the current−voltage characteristics, we determine that (1) the majority of free charge generation is not dependent on the field or temperature and (2) the competition between extraction and recombination of free charges principally determines the dependence of photocurrent on bias. These results are confirmed by direct observation of the temperature dependence of charge separation and recombination using transient absorption spectroscopy and highlight that in order to achieve optimal fill factors in organic solar cells, minimizing free carrier recombination is an important consideration.
Light Induced Charging of Polymer Functionalized Nanorods
Matthias Zorn, Stefan A. L. Weber, Muhammad Nawaz Tahir, Wolfgang Tremel, Hans-Jürgen Butt, Rüdiger Berger, Rudolf Zentel,
Nano Letters, 2010, 10, 2812–2816.
DOI: 10.1021/nl100741n
ZnO nanorods were functionalized with new block copolymers containing a hole transporting moiety in one block and a dye and an anchor system in the second block. After functionalization, the ZnO nanorods are well dispersible in organic media and the fluorescence of the dye is quenched. Kelvin probe force microscopy was used to measure changes in electrical potential between the ZnO nanorod and the polymeric corona. Upon light irradiation, potential changes on the order of some tens of millivolts were observed on individual structures. This effect is attributed to light-induced charge separation between the ZnO nanorod and its hole transporting polymeric corona.
Electrical Scanning Probe Microscopy of an Integrated Blocking Layer S. Weber, M. Memesa, R. Berger, H.-J. Butt, J., S. Gutmann,
Journal of Nanoscience and Nanotechnology, 2010, 10, 1-5.
DOI: 10.1166/jnn.2010.2974
Scanning probe microscopy was performed on an integrated blocking layer system developed for hybrid organic solar cells. A nanocomposite consisting of titania and an amphiphilic triblock copolymer ((PEO)MA-PDMS-MA(PEO)) was prepared by sol-gel chemistry. After plasma treatment and annealing of a spin casted film of 30-100 nm thickness a granular structure with a typical titania grain diameter of 20 nm was found. Conductive scanning force microscopy revealed that on top of almost every grain on the surface there is an increased conductivity compared to the average value. The correlation of grains and conductivity indicated that titania particles formed interconnecting paths through the film. For the resistivity of these pathways we found that effects of tip-sample and sample-electrode resistivity dominate. Additionally, conductive scanning force microscopy revealed non-conducting structures attributed to the thermal treatment. Kelvin probe microscopy of pristine samples on one side and plasma treated plus annealed samples on the other side showed that there is a shift in work function (0.8±0.2 eV) as expected for the transition of amorphous to anatase titania.
(10J3) Orientation of Polymer Functionalized Nanorods in Thin Films
M. Zorn, S. Meuer, M. Tahir, W. Tremel, K. Char, R. Zentel,
J. Nanosci. Nanotechnol., 2010, 10, 6845-6849.
DOI: 10.1166/jnn.2010.2946
A directed self assembly of anisotropic nanostructures offers a possibility to provide unique functional materials, which are e.g., important in optoelectronic devices. We use the liquid crystalline behavior of polymer functionalized TiO2 and ZnO nanorods to apply methods well known for low molecular liquid crystals to achieve oriented thin films. Convective forces in the meniscus on a structured substrate obtain thin layers of oriented nanoparticles with a ordering parameter of S=0.7. As another method we present the orientation of polystyrene covered ZnO nanorods under an applied electric field. The method offers a perpendicular alignment of the rods to the surface.
Heteroheptacenes with Fused Thiophene and Pyrrole Rings Pen Gao, Don Cho, Xiaoyin Y. Yang, Volker Enkelmann, Martin Baumgarten, Klaus Müllen Chem. Eur. J. 2010, 16, 5119-5128.
DOI: 10.1002/chem.200903562
The preparation of conjugated heteroheptacenes using an electrophilic coupling reaction induced by a super acid is reported. The new molecules containing thiophene and/or pyrrole rings are bisbenzo[b,b′]thienodithieno[3,2-b:2′,3′-d]pyrrole, bisbenzo[b,b′]thienocyclopenta[2,1-b:3,4-b′]dithiophene, and bisthieno[3,2-b]thieno[2,3-f:5,4-f′]carbazole. Dithieno[3,2-b:2′,3′-d]pyrrole, cyclopenta[2,1-b:3,4-b′]dithiophene, and carbazole are used as the aromatic cores. This versatility provides access to molecules with systematically controllable physicochemical properties. Single-crystal X-ray analyses demonstrate that the type and position of the alkyl substituents significantly changes the packing properties of the new molecules. The optical and optoelectronic properties of the heteroheptacenes vary considerably depending on the number and position of the sulfur or nitrogen linkages and reveal the improved environmental stability over their hydrocarbon counterparts. The analysis of the experimental results from UV/Vis absorption/photoluminescence (PL) spectroscopy and cyclic voltammetry were combined with DFT quantum-chemical calculations and compared with other model heteroheptacenes. The results suggest that among the acenes with the same number of fused rings, the thiophene ring fusion inside the skeleton stabilizes both HOMO and LUMO levels more effectively than pyrrole and benzene rings. The present study also shows that the new heteroheptacenes are promising candidates for the construction of electronic materials.
Atomically Precise bottom-up Fabrication of Graphene Nanoribbons Jinmimg Cai, Pascal Ruffieux, Rached Jaafar, Marco Bieri, Thomas Braun, Stephan Blankenburg, Matthias Muoth, Ari P. Seitsonen, Moussa Saleh, Xinliang Feng, Klaus Müllen, Roman Fasel, Nature, 2010, 466, 470-473
DOI: 10.1038/nature09211
Graphene nanoribbons—narrow and straight-edged stripes of graphene, or single-layer graphite—are predicted to exhibit electronic properties that make them attractive for the fabrication of nanoscale electronic devices. In particular, although the two-dimensional parent material graphene exhibits semimetallic behaviour, quantum confinement and edge effects should render all graphene nanoribbons with widths smaller than 10 nm semiconducting. But exploring the potential of graphene nanoribbons is hampered by their limited availability: although they have been made using chemical, sonochemical and lithographic methods as well as through the unzipping of carbon nanotubes the reliable production of graphene nanoribbons smaller than 10 nm with chemical precision remains a significant challenge. Here we report a simple method for the production of atomically precise graphene nanoribbons of different topologies and widths, which uses surface-assisted coupling of molecular precursors into linear polyphenylenes and their subsequent cyclodehydrogenation. The topology, width and edge periphery of the graphene nanoribbon products are defined by the structure of the precursor monomers, which can be designed to give access to a wide range of different graphene nanoribbons. We expect that our bottom-up approach to the atomically precise fabrication of graphene nanoribbons will finally enable detailed experimental investigations of the properties of this exciting class of materials. It should even provide a route to graphene nanoribbon structures with engineered chemical and electronic properties, including the theoretically predicted intraribbon quantum dots, superlattice structures and magnetic devices based on specific graphene nanoribbon edge states.
Phenylene Bridged Boron-Nitrogen Containing Dendrimers Agnieszka Pron, Martin Baumgarten, Klaus Müllen, Org. Lett. 2010, 12, 4236-4239.
DOI: 10.1021/ol101327h
The synthesis and characterization of novel phenylene bridged boron−nitrogen containing π-conjugated dendrimers N3B6 and N3B3, with peripheral boron atoms and 1,3,5-triaminobenzene moiety as a core, are presented. UV−vis absorption and emission measurements reveal that the optical properties of the resulting compounds can be controlled by changing the donor/acceptor ratio: a 1:1 ratio results in a more efficient charge transfer than the 1:2 ratio. This was proven by the red shift of the emission maxima and the stronger solvatochromic effect in N3B3 compared to N3B6.