Since the discovery of graphene, there is an increasing amount of research devoted to graphene materials, namely, graphene nanoribbons (GNRs). The “top-down” production of narrow (<10 nm wide), ...unoxidized, and easily processable GNRs with atomically precise edges is challenging, and therefore, new methods need to be developed. We have designed a “bottom-up” approach for the synthesis of very narrow (ca. 0.5 nm) and soluble GNRs using a nonoxidative alkyne benzannulation strategy promoted by Brønsted acid. Suzuki polymerization was used to produce the GNR precursor, a poly(2,6-dialkynyl-p-phenylene) (PDAPP), with a weight-average molecular weight of 37.6 kg mol–1. Cyclization of the ethynylaryl side chains on PDAPP was efficiently achieved using Brønsted acids to ultimately produce the GNRs. Infrared and Raman spectroscopic characterization of the GNRs matches very well with calculated results. The formation of the GNRs was also supported by transmission electron microscopy (TEM) and scanning tunneling microscopy (STM).
Helically Coiled Graphene Nanoribbons Daigle, Maxime; Miao, Dandan; Lucotti, Andrea ...
Angewandte Chemie International Edition,
May 22, 2017, Letnik:
56, Številka:
22
Journal Article
Recenzirano
Graphene is a zero‐gap, semiconducting 2D material that exhibits outstanding charge‐transport properties. One way to open a band gap and make graphene useful as a semiconducting material is to ...confine the electron delocalization in one dimension through the preparation of graphene nanoribbons (GNR). Although several methods have been reported so far, solution‐phase, bottom‐up synthesis is the most promising in terms of structural precision and large‐scale production. Herein, we report the synthesis of a well‐defined, helically coiled GNR from a polychlorinated poly(m‐phenylene) through a regioselective photochemical cyclodehydrochlorination (CDHC) reaction. The structure of the helical GNR was confirmed by 1H NMR, FT‐IR, XPS, TEM, and Raman spectroscopy. This Riemann surface‐like GNR has a band gap of 2.15 eV and is highly emissive in the visible region, both in solution and the solid state.
Made into ribbons: Helicene‐like graphene nanoribbons (HGNR) have been prepared through a regioselective photochemical cyclodehydrochlorination (CDHC) reaction from a polychlorinated polyphenylene precursor.
In snow, water coexists in solid, liquid and vapor states. The relative abundance of the three phases drives snow grain metamorphism and affects the physical properties of the snowpack. Knowledge of ...the content of the liquid phase in snow is critical to estimate the snowmelt runoff and to forecast the release of wet avalanches. Liquid water does not spread homogeneously through a snowpack because different snow layers have different permeabilities; therefore, it is important to track sudden changes in the amount of liquid water within a specific layer. We reproduced water percolation in the laboratory, and used Raman spectroscopy to detect the presence of the liquid phase in controlled snow samples. We performed experiments on both fine- and coarse-grained snow. The obtained snow spectra are well fitted by a linear combination of the spectra typical of liquid water and ice. We progressively charged snow with liquid water from dry snow up to soaked snow. As a result, we exploited continuous, qualitative monitoring of the evolution of the liquid water content as reflected by the fitting coefficient c.
The engineering of acetylenic carbon-rich nanostructures has great potential in many applications, such as nanoelectronics, chemical sensors, energy storage, and conversion, etc. Here we show the ...synthesis of acetylenic carbon-rich nanofibers via copper-surface-mediated Glaser polycondensation of 1,3,5-triethynylbenzene on a variety of conducting (e.g., copper, graphite, fluorine-doped tin oxide, and titanium) and non-conducting (e.g., Kapton, glass, and silicon dioxide) substrates. The obtained nanofibers (with optical bandgap of 2.51 eV) exhibit photocatalytic activity in photoelectrochemical cells, yielding saturated cathodic photocurrent of ca. 10 µA cm
(0.3-0 V vs. reversible hydrogen electrode). By incorporating thieno3,2-bthiophene units into the nanofibers, a redshift (ca. 100 nm) of light absorption edge and twofold of the photocurrent are achieved, rivalling those of state-of-the-art metal-free photocathodes (e.g., graphitic carbon nitride of 0.1-1 µA cm
). This work highlights the promise of utilizing acetylenic carbon-rich materials as efficient and sustainable photocathodes for water reduction.
Bottom-up synthesis of graphene nanoribbons (GNRs) has significantly advanced during the past decade, providing various GNR structures with tunable properties. The synthesis of chiral GNRs, however, ...has been underexplored and only limited to (3,1)-GNRs. We report herein the surface-assisted synthesis of the first heteroatom-doped chiral (4,1)-GNRs from the rationally designed precursor 6,16-dibromo-9,10,19,20-tetraoxa-9a,19a-diboratetrabenzoa,f,j,operylene. The structure of the chiral GNRs has been verified by scanning tunneling microscopy, noncontact atomic force microscopy, and Raman spectroscopy in combination with theoretical modeling. Due to the presence of oxygen–boron–oxygen (OBO) segments on the edges, lateral self-assembly of the GNRs has been observed, realizing well-aligned GNR arrays with different modes of homochiral and heterochiral inter-ribbon assemblies.
Surface-Enhanced Raman Scattering (SERS) can obtain the spectroscopic response of specific analytes. In controlled conditions, it is a powerful quantitative technique. However, often the sample and ...its SERS spectrum are complex. Pharmaceutical compounds in human biofluids with strong interfering signals from proteins and other biomolecules are a typical example. Among the techniques for drug dosage, SERS was reported to detect low drug concentrations, with analytical capability comparable to that of the assessed High-Performance Liquid Chromatography. Here, for the first time, we report the use of SERS for Therapeutic Drug Monitoring of the Anti-Epileptic Drug Perampanel (PER) in human saliva. We used inert substrates decorated with gold NPs deposited via Pulsed Laser Deposition as SERS sensors. We show that it is possible to detect PER in saliva via SERS after an optimized treatment of the saliva sample. Using a phase separation process, it is possible to extract all the diluted PER in saliva from the saliva phase to a chloroform phase. This allows us to detect PER in the saliva at initial concentrations of the order of 10
M, thus approaching those of clinical interest.
Bis(biphenyl)-capped polyynes are investigated to unveil the modulation of the electronic and optical properties of sp-hybridized carbon-atom wires (CAWs) capped with π-conjugated sp2 end groups. ...Raman and surface enhanced Raman spectroscopy experiments and density functional theory (DFT) calculations reveal structural changes from polyyne-like with alternating single–triple bonds toward cumulene-like with more equalized bonds as a consequence of the charge transfer occurring when wires interact with metallic nanoparticles. While polyynes have semiconducting electronic properties, a more equalized system tends to a cumulene-like structure characterized by a nearly metallic behavior. The effect of different sp2 end groups in driving a semiconductor-to-metal transition is investigated by DFT calculations on a series of CAWs capped with different terminations. We discuss how the modulation of the structural, electronic, and vibrational properties of the sp-carbon chain toward the metallic wire is not trivial and requires a suitable chemical design of the end group and control of charge transfer. These results provide a guideline for the design of novel sp–sp2 hybrid carbon nanosystems with tunable properties, where graphene-like and polyyne-like domains are closely interconnected. The capability to tune the final electronic or optical response of the material makes these hybrid sp–sp2 systems appealing for a future all-carbon-based science and technology.
Two unprecedented porphyrin fused nanographene molecules, 1 and 2, have been synthesized by the Scholl reaction from tailor‐made precursors based on benzomtetraphene‐substituted porphyrins. The ...chemical structures were validated by a combination of high‐resolution matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (HR MALDI‐TOF MS), IR and Raman spectroscopy, and scanning tunnelling microscopy (STM). The UV‐vis‐near infrared absorption spectroscopy of 1 and 2 demonstrated broad and largely red‐shifted absorption spectra extending up to 1000 and 1400 nm, respectively, marking the significant extension of the π‐conjugated systems.
Triple whammy: Triply fused porphyrin‐nanographene conjugates (1 and 2) have been synthesized by the Scholl reaction using tailor‐made porphyrin based precursors. The conjugates show broad and intense near‐infrared absorption. The self‐assembled bilayer of 2 was observed at the trichlorobenzene/highly oriented pyrolytic graphite (HOPG) interface.
Laser synthesis emerges as a suitable technique to produce ligand-free nanoparticles, alloys and functionalized nanomaterials for catalysis, imaging, biomedicine, energy and environmental ...applications. In the last decade, laser ablation and nanoparticle generation in liquids has proven to be a unique and efficient technique to generate, excite, fragment and conjugate a large variety of nanostructures in a scalable and clean way. In this work, we give an overview on the fundamentals of pulsed laser synthesis of nanocolloids and new information about its scalability towards selected applications. Biomedicine, catalysis and sensing are the application areas mainly discussed in this review, highlighting advantages of laser-synthesized nanoparticles for these types of applications and, once partially resolved, the limitations to the technique for large-scale applications.
A theoretical approach based on Periodic Boundary Conditions (PBC) and a Linear Combination of Atomic Orbitals (LCAO) in the framework of the density functional theory (DFT) is used to investigate ...the molecular mechanism that rules the piezoelectric behavior of poly(vinylidene fluoride) (PVDF) polymer in the crystalline β-phase. We present several computational tests highlighting the peculiar electrostatic potential energy landscape the polymer chains feel when they change their orientation by a rigid rotation in the lattice cell. We demonstrate that a rotation of the permanent dipole through chain rotation has a rather low energy cost and leads to a lattice relaxation. This justifies the macroscopic strain observed when the material is subjected to an electric field. Moreover, we investigate the effect on the molecular geometry of the expansion of the lattice parameters in the (a, b) plane, proving that the rotation of the dipole can take place spontaneously under mechanical deformation. By band deconvolution of the IR and Raman spectra of a PVDF film with a high content of β-phase, we provide the experimental phonon wavenumbers and relative band intensities, which we compare against the predictions from DFT calculations. This analysis shows the reliability of the LCAO approach, as implemented in the CRYSTAL software, for calculating the vibrational spectra. Finally, we investigate how the IR/Raman spectra evolve as a function of inter-chain distance, moving towards the isolated chain limit and to the limit of a single crystal slab. The results show the relevance of the inter-molecular interactions on the vibrational dynamics and on the electro-optical features ruling the intensity pattern of the vibrational spectra.
PDF
