Graphene-like Molecules Research Articles

N/S co-doped nanocomposite of graphene oxide and graphene-like organic molecules as all-carbonaceous anode material for high-performance Li-ion batteries

In this study, to enhance the electrochemical performance of graphene-based anodes for Li-ion batteries (LIBs), we synthesized an all-carbonaceous N/S co-doped nanocomposite of graphene oxide (GO) and graphene-like small organic molecules (GOM) using a mild, eco-friendly, one-step hydrothermal method with thiourea (CH4N2S) (denoted as h-N/S-GO/GOM). The thiourea facilitated N/S co-doping and π−π bonding, which improved the interaction between hydrophilic GO and hydrophobic GOM in aqueous solution. Notably, the formation of π−π bonds between GO and GOM created pathways that enhanced electron transfer, thereby promoting efficient Li-ion transport from the electrolyte through the channels during rapid charge–discharge cycles. Additionally, the functional groups resulting from N/S co-doping increased the number of active sites within the nanocomposite. Consequently, the h-N/S-GO/GOM anode demonstrated superior electrochemical performance, achieving an average reversible capacity of 1265 mAh g−1 at 0.1 A g−1 and retaining 83.0 % of its capacity after 200 cycles. Furthermore, the nanocomposite exhibited excellent long-term cycling stability, maintaining a capacity of 688 mAh g−1 even after 1000 cycles at a high current density of 1.0 A g−1. The hierarchical network structure of the all-carbonaceous h-N/S-GO/GOM anode facilitated efficient charge transfer between the electrode and electrolyte through shorter diffusion paths for Li-ion transport and provided additional active sites, contributing to its outstanding electrical performance. The h-N/S-GO/GOM nanocomposite represents a promising alternative to traditional graphite-based anodes, offering a path toward high-performance, eco-friendly LIBs suitable for applications such as electric vehicles and energy storage systems.

4]Rhombene: Solution-Phase Synthesis and Application in Distributed Feedback Lasers With Emission Beyond 830 nm.

Graphene-like molecules with multiple zigzag edges are emerging as promising gain materials for organic lasers. Their emission wavelengths can vary widely, ranging from visible to near-infrared (NIR), as the molecular size increases. Specifically, rhombus-shaped molecular graphenes with two pairs of parallel zigzag edges, known as [n]rhombenes, are excellent candidates for NIR lasers due to their small energy gaps. However, synthesizing large-size rhombenes with emission beyond 800 nm in solution remains a significant challenge. In this study, we present a straightforward synthesis of an aryl-substituted [4]rhombene derivative, [4]RB-Ar, using a method that combines intramolecular radical-radical coupling with Bi(OTf)3-mediated cyclization of vinyl ethers. The structure of [4]RB-Ar was confirmed through X-ray crystallographic analysis. Bond length analysis and theoretical calculations indicate that aromatic sextets are predominantly localized along the molecule's long axis. Significantly, [4]RB-Ar demonstrates narrow amplified spontaneous emission at around 834 nm when dispersed in polystyrene thin films. Moreover, solution-processed distributed feedback lasers employing [4]RB-Ar as the active gain material display tunable narrow emissions in the range of 830 to 844 nm.

Circumpentacene with Open-Shell Singlet Diradical Character.

Circumacenes (CAs) are a distinctive type of benzenoid polycyclic aromatic hydrocarbons where an acene unit is completely enclosed by a layer of outer fused benzene rings. Despite their unique structures, the synthesis of CAs is challenging, and until recently, the largest CA molecule synthesized was circumanthracene. In this study, we report the successful synthesis of an extended circumpentacene derivative 1, which represents the largest CA molecule synthesized to date. Its structure was confirmed by X-ray crystallographic analysis and its electronic properties were systematically investigated by both experiments and theoretical calculations. It shows a unique open-shell diradical character due to the existence of extended zigzag edges, with a moderate diradical character index (y0 =39.7 %) and a small singlet-triplet energy gap (ΔES-T =-4.47 kcal/mol). It exhibits a dominant local aromatic character with π-electrons delocalized in the individual aromatic sextet rings. It has a small HOMO-LUMO energy gap and displays amphoteric redox behavior. The electronic structures of its dication and dianion can be considered as doubly charged structures in which two coronene units are fused with a central aromatic benzene ring. This study provides a new route toward stable multizigzag-edged graphene-like molecules with open-shell di/polyradical character.

Fused Triangulene Dimers: Facile Synthesis by Intramolecular Radical-Radical Coupling and Application for Near-Infrared Lasers.

Large graphene-like molecules with four zigzag edges are ideal gain medium materials for organic near-infrared (NIR) lasers. However, synthesizing them becomes increasingly challenging as the molecular size increases. In this study, we introduce a new intramolecular radical-radical coupling approach and successfully synthesize two fused triangulene dimers (1 a/1 b) efficiently. X-ray crystallographic analysis of 1 a indicates that there is no intermolecular π-π stacking in the solid state. When the more soluble derivative 1 b is dispersed in polystyrene thin films, amplified spontaneous emission in the NIR region is observed. Using 1 b as the active gain material, we fabricate solution-processed distributed feedback lasers that exhibit a narrow emission linewidth at around 790 nm. The laser devices also exhibit low thresholds with high photostability. Our study provides a new synthetic strategy for extended nanographenes, which have diverse applications in electronics and photonics.

Programmable zigzag π-extension toward graphene-like molecules by the stacking of naphthalene blocks

Programmable zigzag π-extension toward graphene-like molecules by the stacking of naphthalene blocks

Detailed atomic/molecular-level/electronic-scale computer modeling and electrochemical explorations of the adsorption and anti-corrosion effectiveness of the green nitrogen-based phytochemicals on the mild steel surface in the saline solution

High corrosion protection performance and eco-friendly properties have made the plants' extracts as effective corrosion inhibitors for mild steel in chloride-containing media. The presence of nitrogen-based functionalities in the Papaver somniferum leaves/stem molecules made it a high-efficient corrosion inhibitor in simulated seawater. The adsorption of graphene-like molecules of Papaver sominiferum on the substrate was studied theoretically (by molecular dynamic (MD), Monte Carlo (MC), and density functional theory (DFT)) and experimentally by taking the advantages of Fourier transform infrared spectroscopy (FT-IR), grazing incidence X-ray diffraction (GI-XRD), Raman spectroscopy, ultraviolet-visible (UV–Vis) test, atomic force microscope (AFM), field emission scanning electron microscope (FE-SEM), and contact angle (CA) method. Moreover, the corrosion inhibition degrees and mechanism of the Papaver sominiferum extract (PSE) in different concentrations were examined through the potentiodynamic polarization spectroscopy (PPS) and electrochemical impedance spectroscopy (EIS). EIS outcomes evidenced that by addition of 1600 ppm of PSE to the 3.5% wt. NaCl media, an inhibition efficiency (IE) of 91%, was achieved. In particular, the Nyquist diagram illustrated that the system resistance reached approximately 15 kΩ.cm2 in the case of the PSE1600 sample. The FE-SEM images and Raman spectroscopy results affirmed the steel surface coverage by an inhibitive graphene-like film. Actually, the construction of some complexes such as p-tert-Pentyl-N,N-bis(3-phenylpropyl)aniline, and iron cyanide was reported by GI-XRD analysis. Additionally, the PSE molecules adsorption on the mild steel surface was also proved by the comprehensive theoretical studies.

Magic Number Theory of Superconducting Proximity Effects and Wigner Delay Times in Graphene-Like Molecules

When a single molecule is connected to external electrodes by linker groups, the connectivity of the linkers to the molecular core can be controlled to atomic precision by appropriate chemical synthesis. Recently, the connectivity dependence of the electrical conductance and Seebeck coefficient of single molecules has been investigated both theoretically and experimentally. Here we study the connectivity dependence of the Wigner delay time of single-molecule junctions and the connectivity dependence of superconducting proximity effects, which occur when the external electrodes are replaced by superconductors. Although absolute values of transport properties depend on complex and often uncontrolled details of the coupling between the molecule and electrodes, we demonstrate that ratios of transport properties can be predicted using tables of 'magic numbers,' which capture the connectivity dependence of superconducting proximity effects and Wigner delay times within molecules. These numbers are calculated easily, without the need for large-scale computations. For normal-molecule-superconducting junctions, we find that the electrical conductance is proportional to the fourth power of their magic numbers, whereas for superconducting-molecule-superconducting junctions, the critical current is proportional to the square of their magic numbers. For more conventional normal-molecule-normal junctions, we demonstrate that delay time ratios can be obtained from products of magic number tables.

Configuration-Controllable E/Z Isomers Based on Tetraphenylethene: Synthesis, Characterization, and Applications

Configuration-controllable E/Z isomers based on tetraphenylethene were prepared with a facile and effective method. First, compounds 1 and 2, configuration-controllable precursors of E/Z isomers, were synthesized. Then, pure E/Z isomers were obtained via Suzuki reaction, avoiding the difficulties of separation. The conformational changes of E/Z isomers can occur through photoactivation. Importantly, red-shifts of 66 nm from 6 (E-) to 3 (Z-) and 58 nm from 7 (E-) to 4 (Z-) were observed remarkably on the photoluminescence (PL) emission spectra. The Z isomer showed a longer fluorescence lifetime compared with the E isomer. The Z isomers 3 and 4 exhibited piezofluorochromism under grinding, whereas the E isomers 6 and 7 showed no such behaviors. The E isomer has better thermal stability than the Z isomer. Lastly, graphene-like molecules were synthesized with the FeCl3/CH3NO2 system. The E and Z isomers after oxidation showed negligible differences in the PL emission spectra because the effective conjugated lengths of oxidized E and Z isomers were both extended. Furthermore, the fabricated field-effect transistors showed nice performance with mobilities of 0.92 and 1.14 cm-2 V-1 s-1 at low operating voltages, respectively.

In Ukrainian

The features of the interaction of hydrogen molecules with graphene-like planes in which two carbon atoms are replaced by nitrogen or boron atoms are investigated by methods of quantum chemistry (DFT, B3LYP, 6-31G**). To take into account the dispersion contributions to the energy of the formation of intermolecular complexes that arise in the formation of adsorption supramolecular structures, the dispersion correction Grimme-D3 is used. To study the influence of the size of the graphene-like cluster on the molecular hydrogen chemisorption energy in the model of graphene nanoparticles, polyaromatic molecules (PAM) pyrene, coronene (Cor) and that of 54 carbon atoms, as well as their nitrogen and boron-containing analogues, in which the atoms of nitrogen and boron are placed in a para-position in relation to one another, in the so-called piperazine configuration of the atoms of nitrogen or boron. Equilibrium spatial structures of reagent molecules, formed complexes and products of dissociative chemisorption of hydrogen molecules were found by minimizing the norm of a gradient of total energy. An important stage in the transformation of physically sorbed H2 molecules on the surface of the most carbon materials is its decomposition into two hydrogen atoms that can bind to different carbon atoms of model molecules. In this case, a significant number of different reaction products of the same gross composition is formed. The lowest energy among them is related to one where the atoms of the hydrogen are bound to carbon atoms that are adjacent to the nitrogen or boron atoms. It has been found that, regardless of the size of the carbon PAM, the value of the chemisorption energy in all cases has a positive value and is greater than 100 kJ/mol. The chemisorption energy of the hydrogen molecule by PAM with heteroatoms depends on the size of the model, the position of the atoms of nitrogen and boron and, for the most part, has a small negative value (up to -35 kJ/mole), which indicates the spontaneity of the corresponding process. Calculations have shown that the lowest activation energy of the reaction of the H2 molecule with boron PAM, and the most - for pure carbon PAM, regardless of the size of the models. The nature of the heteroatom changes the structure of the transition state and the mechanism of chemisorption. Analysis of the results of quantum chemical calculations showed the highest exothermicity of dissociative adsorption of H2 molecule on boron-containing graphene-like molecules. For nitrogen-containing surfactants, the reaction is slightly less exothermic, as well as the possibility of desorption of atomic hydrogen from the surface of the latter with subsequent recombination in the gas phase. At the same time, for the models of pure graphene-like layer, these data indicate that chemosorption of molecular hydrogen is impossible. Without a total analysis of the results of all possible placements of a pair of hydrogen atoms (formed by the dissociation of the H2 molecule) when they are bound to nitrogen-containing polyaromatic molecules, it can be noted that the dissociation chemisorption of the H2 molecule, regardless of the nature of the heteroatom in the PAM, is thermodynamically more probable at the periphery of the model molecules than in their center.

Graphene‐like Molecules with Four Zigzag Edges

An efficient synthetic method toward graphene-like molecules (GLMs), having four zigzag edges, is described. They were obtained as stable materials and their structures were confirmed by X-ray crystallographic analysis. They exhibit topology- and size-dependent electronic properties and global aromaticity, which are all different from GLMs having either all-armchair edges, or three zigzag edges, or two armchair/two zigzag edges. They can be reversibly oxidized and reduced into stable charged species, which show fragmental aromatic character to minimize anti-aromaticity. Our studies give some new insights into the electronic structures and properties of a new type of rarely studied GLMs.

Graphene‐like Molecules with Four Zigzag Edges

AbstractAn efficient synthetic method toward graphene‐like molecules (GLMs), having four zigzag edges, is described. They were obtained as stable materials and their structures were confirmed by X‐ray crystallographic analysis. They exhibit topology‐ and size‐dependent electronic properties and global aromaticity, which are all different from GLMs having either all‐armchair edges, or three zigzag edges, or two armchair/two zigzag edges. They can be reversibly oxidized and reduced into stable charged species, which show fragmental aromatic character to minimize anti‐aromaticity. Our studies give some new insights into the electronic structures and properties of a new type of rarely studied GLMs.

The electron density function of the Hückel (tight-binding) model

The Hückel (tight-binding) molecular orbital (HMO) method has found many applications in the chemistry of alternant conjugated molecules, such as polycyclic aromatic hydrocarbons (PAHs), fullerenes and graphene-like molecules, as well as in solid-state physics. In this paper, we found analytical expressions for the electron density matrix of the HMO method in terms of odd-powers of its Hamiltonian. We prove that the HMO density matrix induces an embedding of a molecule into a high-dimensional Euclidean space in which the separation between the atoms scales very well with the bond lengths of PAHs. We extend our approach to describe a quasi-correlated tight-binding model, which quantifies the number of unpaired electrons and the distribution of effectively unpaired electrons. In this case, we found that the corresponding density matrices induce embedding of the molecules into high-dimensional Euclidean spheres where the separation between the atoms contains information about the spin–spin repulsion between them. Using our approach, we found an analytic expression which explains the bond length alternation in polyenes inside the HMO framework. We also found that spin–spin interaction explains the alternation of distances between pairs of atoms separated by two bonds in conjugated molecules.

Remarkable Magnetic Coupling Interactions in Multi-Beryllium-Expanded Small Graphene-like Molecules with Well-Defined Polyradical Characters

Multi-beryllium-expanded small graphene-like molecules including oligoacenes (mBe-nA) and graphene patches (mBe-GP) are computationally designed through introducing two or three Be atoms into the specific benzenoid rings of the graphene-like molecules, leading to replacement of some C–C bonds by the C–Be–C linkages with elongated C···C distances of about 3.3 Å in them. As a result, the elongation of the C···C bonds and insertion of more Be atoms make the two radical moieties in each molecule relatively separated and their interaction relatively weak. Both density functional theory and CASSCF calculations indicate that all these multi-Be-expanded graphene-like molecules exhibit well-defined polyradical characters: an open-shell singlet diradical for all mBe-nA and an open-shell singlet diradical or quintet tetraradical for mBe-GP depending on the Be-insertion patterns of the patches. The main findings in this work are that (i) a switching from the parent graphene-like closed-shell molecules (e.g., linear oligoacenes and graphene patches) to the open-shell singlet (diradical) or quintet (tetraradical) ground states can be realized by introducing Be as linkers into the graphene-like molecules; (ii) more importantly, the spin-coupling interactions of such mBe-nA and mBe-GP are remarkably large; and (iii) in these Be-modified molecules the Be–C bonds exhibit considerable covalent character and the Be···Be distances are 2.67–2.84 Å, implying weak Be(s2)···Be(s2) metallophilic interaction. This work would open a new perspective for the rational design of perfect and stable singlet diradicals or polyradicals with large spin-coupling constants on the basis of small closed-shell graphene-like molecules by multimetal incorporation and also encourage experimentalists to pursue and realize these interesting structures with enhanced magnetic properties in the future.

Effect of carbon-layer rearrangement on one- and two-photon absorption properties in the alternative graphene-like hybrids – A theoretical investigation

In this work, novel alternative graphene-like hybrids covalent with porphyrin (porphyrin-graphene-like hybrids) are designed, named TPP-gra(n)-a and TPP-gra(n)-b (n = 1–5), respectively. Moreover, the differences in their electronic structures, one-photon absorption (OPA) and two-photon absorption (TPA) properties are revealed by theoretical chemistry calculations. Our study shows that the rearrangement of carbon-atom layers of the hybrids can effectively enhance electronic delocalization, bringing about outstanding TPA properties. In addition to the increase of the graphene-like size, substituting porphyrin into different active-carbon of graphene-like molecules can cause better polarization of TPP-gra(n)-b series than TPP-gra(n)-a series, resulting in TPP-gra(n)-b series possess relatively higher TPA cross sections (δTPA) than that of corresponding TPP-gra(n)-a compounds, such as TPP-gra3-b, TPP-gra4-b and TPP-gra5-b, whose δTPA can be as large as 5686.2–19496.6 GM ranging from 535.8 to 579.4 nm. The carbon-based materials possessing relatively high δTPA values have a great potential for applications in optoelectronic devices and optical limiting fields. Consequently, we expect the calculations can provide a theoretical perspective for further studies on TPA materials based on graphene.

Magnetization plateaus and the susceptibilities of a nano-graphene sandwich-like structure

Ising model with the anisotropy is abstracted based on a nano-graphene sandwich-like structure. The system consists of a ferromagnetic middle layer and two antiferromagnetic layers on the top and under the bottom. Multiple spin states are employed to the analysis of magnetic behavior for graphene-like molecules. The effective-field theory with correlations has been successfully applied to this, and the general formula of the magnetic properties for the nano-graphene sandwich-like structure is obtained. Results of numerical calculation for the magnetization and the susceptibilities are discussed for specific values of the external magnetic field. Magnetization plateaus appear on the magnetization curves at low temperature. The exchange coupling, the anisotropy and the external magnetic field have important roles on the magnetic properties for the nano-graphene sandwich-like structure.

Two-Dimensional Icy Water Clusters Between a Pair of Graphene-Like Molecules or Graphene Sheets

To understand the 2-dimensional (2D) structural evolution of water molecules intercalated into a graphene bilayer, the geometries of water clusters up to tridecamer formed between a pair of graphene sheets or between graphene-like molecules (coronene and dodecabenzocoronene) are investigated. Due to their large sizes, the self-consistent-charge density-functional tight-binding (SCC-DFTB) method expanded into the third order and supplemented with a Slater–Kirkwood dispersion term was used. In this way both hydrogen bonding and H−π/π–π interactions are calculated in a balanced manner with the right magnitude of binding energies very close to the reference values based on the most accurate ab initio results. It should be noted that conventional density functional theory (DFT) calculations underestimate the H−π/π–π interaction, while dispersion-corrected DFT calculations overestimate hydrogen bonding. The latter method is also employed for comparison and to confirm the reliability of the SCC-DFTB results. For (H2O)6, the fused bitetragonal hexamer is nearly isoenergetic to the most stable planar hexagonal ring structure, and it is more frequently found. In (H2O)10 and (H2O)13 clusters, a tetragon is the most frequent geometry followed by a pentagon, while the hexagon is less frequent. These results certainly provide evidence of the recent planar tetragonal ice structure found inside a graphene bilayer (Nature 2015, 519, 443) which is in contrast to the well-known hexagonal pattern of the bulk ice. This structural change from hexagonal to tetragonal network on the graphene surface is attributed mainly to the inherent nature of 2D water.

Graphene and Graphene-like Molecules: Prospects in Solar Cells.

Graphene is constantly hyped as a game-changer for flexible transparent displays. However, to date, no solar cell fabricated on graphene electrodes has out-performed indium tin oxide in power conversion efficiency (PCE). This Perspective covers the enabling roles that graphene can play in solar cells because of its unique properties. Compared to transparent and conducting metal oxides, graphene may not have competitive advantages in terms of its electrical conductivity. The unique strength of graphene lies in its ability to perform various enabling roles in solar cell architectures, leading to overall improvement in PCE. Graphene can serve as an ultrathin and transparent diffusion barrier in solar cell contacts, as an intermediate layer in tandem solar cells, as an electron acceptor, etc. Inspired by the properties of graphene, chemists are also designing graphene-like molecules in which the topology of π-electron array, donor-acceptor structures, and conformation can be tuned to offer a new class of light-harvesting materials.

Exploring quantum interference in heteroatom-substituted graphene-like molecules.

If design principles for controlling quantum interference in single molecules could be elucidated and verified, then this will lay the foundations for exploiting such effects in nanoscale devices and thin-film materials. When the core of a graphene-like polyaromatic hydrocarbon (PAH) is weakly coupled to external electrodes by atoms i and j, the single-molecule electrical conductance σij depends on the choice of connecting atoms i,j. Furthermore, provided the Fermi energy is located between the HOMO and LUMO, conductance ratios σij/σlm corresponding to different connectivities i,j and l,m are determined by quantum interference within the PAH core. In this paper, we examine how such conductance ratios change when one of the carbon atoms within the 'parent' PAH core is replaced by a heteroatom to yield a 'daughter' molecule. For bipartite parental cores, in which odd-numbered sites are connected to even-numbered sites only, the effect of heteroatom substitution onto an odd-numbered site is summarized by the following qualitative rules: (a) when i and j are odd, both parent and daughter have low conductances, (b) when i is odd and j is even, or vice versa both parent and daughter have high conductances and (c) when i,j are both even, the parent has a low conductance and the daughter a high conductance. These rules are verified by comparison with density-functional calculations on naphthalene, anthracene, pyrene and anthanthrene cores connected via two different anchor groups to gold electrodes.

Searching the Hearts of Graphene-like Molecules for Simplicity, Sensitivity, and Logic.

If quantum interference patterns in the hearts of polycyclic aromatic hydrocarbons could be isolated and manipulated, then a significant step toward realizing the potential of single-molecule electronics would be achieved. Here we demonstrate experimentally and theoretically that a simple, parameter-free, analytic theory of interference patterns evaluated at the mid-point of the HOMO-LUMO gap (referred to as M-functions) correctly predicts conductance ratios of molecules with pyrene, naphthalene, anthracene, anthanthrene, or azulene hearts. M-functions provide new design strategies for identifying molecules with phase-coherent logic functions and enhancing the sensitivity of molecular-scale interferometers.

Magic ratios for connectivity-driven electrical conductance of graphene-like molecules.

Experiments using a mechanically controlled break junction and calculations based on density functional theory demonstrate a new magic ratio rule (MRR) that captures the contribution of connectivity to the electrical conductance of graphene-like aromatic molecules. When one electrode is connected to a site i and the other is connected to a site i' of a particular molecule, we assign the molecule a "magic integer" Mii'. Two molecules with the same aromatic core but different pairs of electrode connection sites (i,i' and j,j', respectively) possess different magic integers Mii' and Mjj'. On the basis of connectivity alone, we predict that when the coupling to electrodes is weak and the Fermi energy of the electrodes lies close to the center of the HOMO-LUMO gap, the ratio of their conductances is equal to (Mii'/Mjj')(2). The MRR is exact for a tight-binding representation of a molecule and a qualitative guide for real molecules.