Codoped germanene with 3p and 4p elements elements.

CONTEXT: The relentless need for new materials to be used in electronic devices has opened new research directions in materials science. One of them involves using two-dimensional materials, among which there is current interest in using germanene. The heteroatom doping of germanene has been proposed as a possible approach to fine-tuning its electronic properties. However, this procedure is complicated because locating the dopants with a specific arrangement is challenging, thus achieving reproducibility. To avoid this problem, we propose the codoping of germanene to understand if dopants prefer to be agglomerated as observed for graphene or if they prefer to adopt a random disposition. Herein, we employed first-principles calculations to study 21 codoped germanene systems with one 3p (Al, Si, P, and S) and one 4p (Ga, As, and Se) element. Our results indicate that in the cases of AlP, AlS, GaP, GaS, GaAs, and GaSe codoped germanene, the dopants show a tendency to be located in specific lattice positions. The ortho disposition of dopants is preferred for AlP, AlS, GaP and GaS codoped germanene and their 4p counterparts GaAs and GaSe codoped germanene, and the materials showed interesting electronic properties making them suitable to develop germanene-based electronic materials. METHODS: We utilized the M06-L, HSE06 methods accompanied by the 6-31G* basis sets to perform periodic boundary conditions calculations as implemented in Gaussian 09. The unit cells were sampled employing 100 k-points for geometry optimizations and 2000 k-points for electronic properties The ultrafine grid was employed. Results were visualized employing Gaussview 5.0.1. In addition to this, we performed B3LYP-D3 periodic calculations as implemented in CRYSTAL17.

Unveiling a New 2D Semiconductor: Biphenylene-Based InN.

The two-dimensional (2D) materials class earned a boost in 2021 with biphenylene synthesis, which is structurally formed by the fusion of four-, six-, and eight-membered carbon rings, usually named 4-6-8-biphenylene network (BPN). This research proposes a detailed study of electronic, structural, dynamic, and mechanical properties to demonstrate the potential of the novel biphenylene-like indium nitride (BPN-InN) via density functional theory and molecular dynamics simulations. The BPN-InN has a direct band gap energy transition of 2.02 eV, making it promising for optoelectronic applications. This structure exhibits maximum and minimum Young modulus of 22.716 and 22.063 N/m, Poisson ratio of 0.018 and -0.008, and Shear modulus of 11.448 and 10.860 N/m, respectively. To understand the BPN-InN behavior when subjected to mechanical deformations, biaxial and uniaxial strains in armchair and zigzag directions from -8 to 8% were applied, achieving a band gap energy modulation of 1.36 eV over tensile deformations. Our findings are expected to motivate both theorists and experimentalists to study and obtain these new 2D inorganic materials that exhibit promising semiconductor properties.

Covalent functionalization of germanene employing computational simulations.

Computational simulations through density functional theory in conjunction with M06-L and HSE functional have been carried out to investigate the chemical reactivity of the germanene monolayer. It is exceptionally reactive, with an average reaction energy of -60.4 kcal mol-1 for the nineteen functional groups considered: H, F, Cl, Br, O, S, Se, Ge, OH, SH, CH3, CF3, NH, NH2, C6H5, C6H4, CCl2, CBr2, and the azomethine ylide. The results indicate that oxygen is the most reactive reagent (-96.9 kcal mol-1), followed by fluorine (-83.1 kcal mol-1). Germanene presents a rich organic chemistry, and functionalization with azomethine ylides, benzynes, and carbenes can be easily accomplished as indicated by the reaction energies computed, which lie between -45 and -65 kcal mol-1. Furthermore, germanene is significantly more reactive than graphene and hexagonal boron nitride monolayers since the reaction energy for germanene is more than 40 kcal mol-1 lower. Although, in general, germanene is slightly more reactive than black and blue phosphorene and less prone to oxidation, but its oxidation when exposed to air occurs spontaneously. The addition of functional groups works cooperatively. The reaction energies become lower as the number of functional groups increases, thus favouring the agglomeration of functional groups attached unless the steric effect alters this pattern. Finally, we analyzed the electronic properties of functionalized germanene. It is possible to fine-tune the band gap of germanene from 0.1 to 2 eV using different functional groups and coverages. For O-50% and S-50% functionalized germanene, we found that carrier recombination is the most difficult due to the considerable differences between the effective masses of holes and electrons, which is promising for optical applications.

Chemical reactivity of graphene doped with 3d transition metals: nothing compares to a single vacancy.

CONTEXT: Finding catalysts that do not rely on the use of expensive metals is one of the requirements to achieve sustainable production. The reactivity of graphene doped with 3d transition metals was studied. All dopants enhanced the reactivity of graphene and performed better than Stone-Wales defects and divacancies, but were inferior to monovacancies. For hydrogenation of doped-monovacancies, Sc, Ti, Cr, Co, and Ni induced more prominent reactivity on the carbon atoms. However, the metals were the most reactive center for V, Mn, and Fe-doped graphene. Cu and Zn turned the four neighboring carbon atoms into the preferred sites for hydrogenation. The addition of oxygen to doped graphene with Ti, V, Cr, Mn, Fe, Co, and Ni on a monovacancy revealed a more uniform pattern since the metal, preferred to react with oxygen. However, Sc induced a larger reactivity on the carbon atoms. The affinity of the 3d metal-doped graphene systems towards oxygen was inferior to that observed for single-vacancies. Therefore, vacancy engineering is the most favorable and least expensive method to enhance the reactivity of graphene. METHODS: We applied Truhlar's M06-L method accompanied by the 6-31G* basis sets to perform periodic boundary conditions calculations as implemented in Gaussian 09. The ultrafine grid was employed and the unit cells were sampled employing 100 k-points. Results were visualized employing Gaussview 5.0.1.

Theoretical Characterization of Germanene Doped with Main Group Elements.

Herein, using density functional calculations, we studied the substitutional doping in germanene with B, C, N, O, Al, Si, P, S, Ga, As, and Se. Nitrogen is the element that can be more easily incorporated into the germanene lattice, followed by silicon, carbon, and boron. Almost all dopants were efficient in opening a band-gap. Yet, caution should be taken because this opening strongly depends on the dopant concentration. Carbon and sulfur were the most effective elements for band-gap opening. C-doping generates the lowest effective masses (me*/m0=mh*/m0=0.09). The equal me and mh values indicate an intrinsic semiconductor behavior, a characteristic shared by the chalcogenides-doped systems. Additionally, we performed a detailed analysis of the preferred disposition of dopants in the germanene lattice. In contrast with the results obtained for graphene, when multiple atoms are introduced in the germanene framework, they do not prefer to be agglomerated, adopting a random disposition, except in the case of sulfur and nitrogen, which favored specific dopant arrangement. Two sulfur dopants showed a notorious preference for replacing a Ge-Ge bond but without forming an S-S linkage, thus adopting a thiophene-like structure that may impart germanene exciting properties, as observed for S and N codoped graphene.

Platinum and Palladium Organometallic Compounds: Disrupting the Ergosterol Pathway in Trypanosoma cruzi.

Current treatment for Chagas' disease is based on two drugs, Nifurtimox and Benznidazol, which have limitations that reduce the effectiveness and continuity of treatment. Thus, there is an urgent need to develop new, safe and effective drugs. In previous work, two new metal-based compounds with trypanocidal activity, Pd-dppf-mpo and Pt-dppf-mpo, were fully characterized. To unravel the mechanism of action of these two analogous metal-based drugs, high-throughput omics studies were performed. A multimodal mechanism of action was postulated with several candidates as molecular targets. In this work, we validated the ergosterol biosynthesis pathway as a target for these compounds through the determination of sterol levels by HPLC in treated parasites. To understand the molecular level at which these compounds participate, two enzymes that met eligibility criteria at different levels were selected for further studies: phosphomevalonate kinase (PMK) and lanosterol 14-α demethylase (CYP51). Molecular docking processes were carried out to search for potential sites of interaction for both enzymes. To validate these candidates, a gain-of-function strategy was used through the generation of overexpressing PMK and CYP51 parasites. Results here presented confirm that the mechanism of action of Pd-dppf-mpo and Pt-dppf-mpo compounds involves the inhibition of both enzymes.

Mode of action of p-quinone derivatives with trypanocidal activity studied by experimental and in silico models.

Quinones are attractive pharmacological scaffolds for developing new agents for the treatment of different transmissible and non-transmissible human diseases due to their capacity to alter the cell redox homeostasis. The bioactivity and potential mode of action of 19 p-quinone derivatives fused to different aromatic rings (carbo or heterocycles) and harboring distinct substituents were investigated in infective Trypanosoma brucei brucei. All the compounds, except for a furanequinone (EC50=38 µM), proved to be similarly or even more potent (EC50 = 0.5-5.5 µM) than the clinical drug nifurtimox (EC50 = 5.3 µM). Three furanequinones and one thiazolequinone displayed a higher selectivity than nifurtimox. Two of these selective hits resulted potent inhibitors of T. cruzi proliferation (EC50=0.8-1.1 µM) but proved inactive against Leishmania infantum amastigotes. Most of the p-quinones induced a rapid and marked intracellular oxidation in T. b. brucei. DFT calculations on the oxidized quinone (Q), semiquinone (Q•-) and hydroquinone (QH2) suggest that all quinones have negative ΔG for the formation of Q•-. Qualitative and quantitative structure-activity relationship analyses in two or three dimensions of different electronic and biophysical descriptors of quinones and their corresponding bioactivities (killing potency and oxidative capacity) were performed. Charge distribution over the quinone ring carbons of Q and Q.- and the frontier orbitals energies of SUMO (Q.-) and LUMO (Q) correlate with their oxidative and trypanocidal activity. QSAR analysis also highlighted that both bromine substitution in the p-quinone ring and a bulky phenyl group attached to the furane and thiazole rings (which generates a negative charge due to the π electron system polarized by the nearby heteroatoms) are favorable for activity. By combining experimental and in silico procedures, this study disclosed important information about p-quinones that may help to rationally tune their electronic properties and biological activities.

Heteroatom Codoped Graphene: The Importance of Nitrogen.

Although graphene has exceptional properties, they are not enough to solve the extensive list of pressing world problems. The substitutional doping of graphene using heteroatoms is one of the preferred methods to adjust the physicochemical properties of graphene. Much effort has been made to dope graphene using a single dopant. However, in recent years, substantial efforts have been made to dope graphene using two or more dopants. This review summarizes all the hard work done to synthesize, characterize, and develop new technologies using codoped, tridoped, and quaternary doped graphene. First, I discuss a simple question that has a complicated answer: When can an atom be considered a dopant? Then, I briefly discuss the single atom doped graphene as a starting point for this review's primary objective: codoped or dual-doped graphene. I extend the discussion to include tridoped and quaternary doped graphene. I review most of the systems that have been synthesized or studied theoretically and the areas in which they have been used to develop new technologies. Finally, I discuss the challenges and prospects that will shape the future of this fascinating field. It will be shown that most of the graphene systems that have been reported involve the use of nitrogen, and much effort is needed to develop codoped graphene systems that do not rely on the stabilizing effects of nitrogen. I expect that this review will contribute to introducing more researchers to this fascinating field and enlarge the list of codoped graphene systems that have been synthesized.

Structural and magnetic properties of a defective graphene buffer layer grown on SiC(0001): a DFT study.

Understanding the role of defects in the magnetic properties of the graphene buffer layer (BL) grown on substrates should be important to provide hints for manufacturing future graphene-based spintronic devices in a controlled fashion. Herein, density functional theory was applied to assess the structure and magnetic properties of defective BL on 6H-SiC(0001). Particularly, we conducted a thorough study of one and two vacancies and Stone-Wales defects in the BL. Our results reveal that the removal of a carbon atom in the BL framework that was originally bonded to a Si atom in the substrate is preferred over that of a sp2-bonded atom. As a result, a hexacoordinated silicon atom is formed with a slightly deviated octahedral geometry. A stable antiferromagnetic (AF) state was verified for the single vacancy system, with a quite different spin-density distribution to the one obtained for the perfect BL. Also, this AF state is nearly degenerate with the non-magnetic and low magnetic states. As for the Stone-Wales defect, the AF sate is almost degenerate with the most stable M = 2 µB magnetic configuration. However, the introduction of two vacancies in the carbon network of BL causes the loss of magnetism of the BL-SiC system. Our theoretical calculations support experimental predictions favoring the BL as the site for single vacancy formation rather than the epitaxial monolayer graphene, by 4.3 eV.

Unraveling the electromagnetic structure of the epitaxial graphene buffer layer.

We have employed density functional theory to study the structural, electronic and magnetic properties of the first all-carbon layer grown epitaxially on 6H-SiC(0 0 0 1). Using VDW-DF, M06-L, LSDA, LSDA+U, PBE and PBE-D2 methods we have performed a comparative study of the preferable magnetic configuration of the system. In this work, for the first time, we report a stable antiferromagnetic (AF) ordering in the buffer layer caused by the presence of silicon dangling bonds in the SiC top layer. This state is nearly degenerated with the ferromagnetic state with a magnetic moment equal to the number of silicon dangling bonds. A net magnetic moment of 0.55 µb per Si dangling bond was found for both states. However, only for the ferromagnetic state the carbon atoms of the buffer layer exhibited a magnetic moment. The magnetic configuration is much more stable than the non-polarized one and might explain SQUID results and spin transport experiments with epitaxial graphene. Furthermore, we found that, as previously observed experimentally, the buffer layer is a true semiconductor.

Theoretical investigation of various aspects of two dimensional holey boroxine, B3O3.

By means of first-principles calculations, we study the structural, electronic and mechanical properties of the newly synthesized boron-oxygen holey framework (Chem. Comm. 2018, 54, 3971). It has a planar structure formed by B3O3 hexagons, which are joined via strong covalent boron-boron bonds. The six B3O3 units are connected with six-fold symmetry exhibiting a large hole with a surface area of 23 Å2, which is ideal for the adsorption of alkalis. For neutral alkalis, we found that the adsorption energy of potassium is 14 and 12 kcal mol-1 larger than those determined for sodium and lithium, respectively. In contrast, for alkali cations, there is a clear preference for lithium over sodium and potassium. With regard to its electronic properties, it is an insulator with an electronic band gap of 5.3 eV, at the HSE level of theory. We further investigate the effect of strain on the band gap and find it a less efficient technique to tune the electronic properties. The wide optical gap of B3O3 can be utilized in ultraviolet (UV) applications, such as UV photodetectors, etc. Additionally, the 2D elastic modulus of B3O3 (53.9 N m-1) is larger than that of Be3N2, silicene, and germanene. Besides, we also report bilayer and graphite-like bulk B3O3 and furthermore, find that the optoelectronic properties of the bilayer can be tuned with an external electric field. The great tunability of optical properties from UV to the visible range offers a vast range of applications in optoelectronics.

Unusual Enhancement of the Adsorption Energies of Sodium and Potassium in Sulfur-Nitrogen and Silicon-Boron Codoped Graphene.

Herein, we have employed first-principles calculations to investigate the interaction between XY dual-doped graphene (DDG) (X = AL, Si, P, S; Y = B, N, O) and sodium/potassium. The introduction of two dopants alters the adsorption energy (AE) of sodium and potassium with respect to perfect graphene by an average of 0.88 and 0.66 eV, respectively. The systems that display the strongest interactions with the two alkalies assayed are SN and SiB DDG. Although the adsorption energy of sodium on graphene is weaker in comparison to that of potassium, the introduction of these dopants significantly reduces this difference. In effect, in some cases, the AE-K and AE-NA differ by less than 0.05 eV. The protrusion of the 3p dopants out of the graphene plane creates a hole where sodium and potassium can easily be intercalated between two layers of dual-doped graphene. The interlayer distances are reduced by less than 0.4 Å after K intercalation, making the process very favorable. Finally, most importantly, this eminent rise in adsorption energies guarantees exceptional storage capacities at the cost of low doping concentration.

Hydrogenation and Fluorination of 2D Boron Phosphide and Boron Arsenide: A Density Functional Theory Investigation.

First-principles density functional theory calculations are performed to study the stability and electronic properties of hydrogenated and fluorinated two-dimensional sp3 boron phosphide (BP) and boron arsenide (BAs). As expected, the phonon dispersion spectrum and phonon density of states of hydrogenated and fluorinated BX (X = P, As) systems are found to be different, which can be attributed to the different masses of hydrogen and fluorine. Hydrogenated BX systems bear larger and indirect band gaps and are found to be different from fluorinated BX systems. These derivatives can be utilized in hydrogen storage applications and ultrafast electronic devices. Finally, we investigated the stability and electronic properties of stacked bilayers of functionalized BP. Interestingly, we found that these systems display strong interlayer interactions, which impart strong stability. In contrast with the electronic properties determined for the fluorinated/hydrogenated monolayers, we found that the electronic properties of these bilayers can finely be tuned to a narrow gap semiconductor, metallic or nearly semimetallic one by selecting a suitable arrangement of layers. Moreover, the nearly linear dispersion of the conduction band edge and the heavy-, light-hole bands are the interesting characteristics. Furthermore, the exceptional values of effective masses assure the fast electronic transport, making this material very attractive to construct electronic devices.

Triple-Doped Monolayer Graphene with Boron, Nitrogen, Aluminum, Silicon, Phosphorus, and Sulfur.

The structure, stability, electronic properties and chemical reactivity of X/B/N triple-doped graphene (TDG) systems (X=Al, Si, P, S) are investigated by means of periodic density functional calculations. In the studied TDGs the dopant atoms prefer to be bonded to one another instead of separated. In general, the XNB pattern is preferred, with the exception of sulfur, which favors the SBN motif. The introduction of a third dopant results in a negligible decrease of the cohesive energies with respect to the dual-doped graphene (DDG) counterparts. Thus, it is expect that these systems can be prepared soon. For SiNB TDG, the introduction of the B dopant reduces the gap opening at the K point and restores the Dirac cones that are destroyed in SiN DDG. On the contrary, for PNB TDG, the bandgap is increased with respect to PN DDG, probably because the introduction of B weakens the PN bonding, and thus the electronic structure is rather similar to that of P-doped graphene. Finally, with regard to the reactivity of the TDGs, for AlNB, PNB, and SNB the carbon atoms are more reactive than in their AlN, PN, and SN DDG counterparts. On the contrary, the reactivity of SiNB is lower than that of SiN DDG. Therefore, to increase the reactivity of graphene, Al, P, and S should be combined with BN motifs.

The effect of the dopant nature on the reactivity, interlayer bonding and electronic properties of dual doped bilayer graphene.

Herein, we report on the structural, chemical reactivity and electronic properties of dual-doped bilayer graphene (DDBG). Only one of the layers was doped with a pair of 3p-2p elements. Aluminum was the only dopant which prefers to interact with the undoped layer. The interlayer interaction energies of DDBG are smaller than those determined for bilayer graphene, except for AlN and AlO DDBG. This effect is due to the presence of weak Al-C interlayer bonds. The dopants increase the reactivity of both the doped and undoped layers. Interestingly, we found that hydrogenation is a method that can be used to switch on/off the interlayer bonding, as it controlled the X-C interlayer distance (X = Al, Si, P, S). The magnetic moment of the systems can be adjusted by the position of the 3p dopant. In effect, when X interacts with the doped layer, the magnetic moment is reduced, while it is maintained when X fails to interact. Finally, we found that the doped layer is able to break the symmetry of the undoped sheet and small gaps can be opened in the band structure of the undoped layer. As observed for single doped monolayer graphene, the most effective element for such purposes is P, which opened gaps close to 0.2 eV. For SiN DDBG, the spin filtering properties are enhanced with respect to the monolayered structure.

Pristine Graphene-Based Catalysis: Significant Reduction of the Inversion Barriers of Adsorbed and Confined Corannulene, Sumanene, and Dibenzo[a,g]corannulene.

Herein, we investigated the inversion of corannulene, sumanene, and dibenzo[a,g]corannulene when they are adsorbed onto graphene or intercalated in bilayer graphene. The results obtained with the M06-L, M06-2X, TPPS-D3, TPSS-D3BJ, B3LYP-D3, and B3LYP-D3BJ methods supported a significant reduction of the inversion barriers. In the case of corannulene adsorbed onto graphene, nonbonded interactions reduce the inversion barrier by at least a 50% with respect to the gas phase, whereas for adsorbed sumanene and dibenzo[a,g]corannulene the reductions are at least 39 and 67%, respectively. When the molecules are intercalated in bilayer graphene the lowering of the activation energy is more significant. In the particular case of dibenzo[a,g]corannulene the molecule is expected to display an almost planar structure, with its 0.83 Å bowl depth almost completely quenched. For intercalated corannulene and sumanene, the inversion barriers are at least 66 and 60% lower, respectively. It is our hope that these results can help to improve the design of receptors that can catalyze the inversion of buckybowls.

Bonding and singlet-triplet gap of silicon trimer: effects of protonation and attachment of alkali metal cations.

We revisit the singlet-triplet energy gap (ΔE(ST)) of silicon trimer and evaluate the gaps of its derivatives by attachment of a cation (H(+), Li(+), Na(+), and K(+)) using the wavefunction-based methods including the composite G4, coupled-cluster theory CCSD(T)/CBS, CCSDT and CCSDTQ, and CASSCF/CASPT2 (for Si3) computations. Both (1)A1 and (3)A2' states of Si3 are determined to be degenerate. An intersystem crossing between both states appears to be possible at a point having an apex bond angle of around α = 68 ± 2° which is 16 ± 4 kJ/mol above the ground state. The proton, Li(+) and Na(+) cations tend to favor the low-spin state, whereas the K(+) cation favors the high-spin state. However, they do not modify significantly the ΔE(ST). The proton affinity of silicon trimer is determined as PA(Si3) = 830 ± 4 kJ/mol at 298 K. The metal cation affinities are also predicted to be LiCA(Si3) = 108 ± 8 kJ/mol, NaCA(Si3) = 79 ± 8 kJ/mol and KCA(Si3) = 44 ± 8 kJ/mol. The chemical bonding is probed using the electron localization function, and ring current analyses show that the singlet three-membered ring Si3 is, at most, nonaromatic. Attachment of the proton and Li(+) cation renders it anti-aromatic.

Stacked functionalized silicene: a powerful system to adjust the electronic structure of silicene.

Herein, we employed first principle density functional periodic calculations to characterize the silicon counterpart of graphene:silicene. We found that silicene is far more reactive than graphene, very stable and strong Si-X bonds can be formed, where X = H, CH3, OH and F. The Si-F bond is the strongest one, with a binding energy of 114.9 kcal mol(-1). When radicals are agglomerated, the binding energy per functional grows up to 17 kcal mol(-1). The functionalization with OH radicals produces the largest alterations of the structure of silicene, due to the presence of intralayer hydrogen bonds. The covalent addition of H, CH3, OH and F to silicene enables the adjustment of its electronic structure. In effect, functionalized silicene can be a semiconductor or even exhibit metallic properties when the type and concentration of radicals are varied. The most interesting results were obtained when two layers of functionalized silicene were stacked, given that the band gaps experienced a significant reduction with respect to those computed for symmetrically and asymmetrically (Janus) functionalized monolayer silicenes. In the case of fluorine, the largest changes in the electronic structure of bilayer silicene were appreciated when at least one side of silicene was completely fluorinated. In general, the fluorinated side induces metallic properties in a large number of functionalized silicenes. In some cases which presented band gaps as large as 3.2 eV when isolated, the deposition over fluorinated silicene was able to close that gap and induce a metallic character. In addition to this, in four cases small gaps in the range of 0.1-0.6 eV were obtained for bilayer silicenes. Therefore, functionalization of silicene is a powerful method to produce stable two-dimensional silicon based nanomaterials with tunable optical band gaps.

Chemical reactivity and band-gap opening of graphene doped with gallium, germanium, arsenic, and selenium atoms.

Herein, the effects of substitutional doping of graphene with Ga, Ge, As, and Se are shown. Ge exhibits the lowest formation energy, whereas Ga has the largest one. Ga- and As-doped graphene display a reactivity that is larger than that corresponding to a double vacancy. They can decompose H2 and O2 easily. Variation of the type and concentration of dopant makes the adjustment of the interlayer interaction possible. In general, doping of monolayer graphene opens a band gap. At some concentrations, Ga doping induces a half metallic behavior. As is the element that offers the widest range of gap tuning. Heyd-Scuseria-Ernzerhof calculations indicate that it can be varied from 1.3 to 0.3 eV. For bilayer graphene, the doped sheet induces charge redistribution in the perfect underneath sheet, which opens a gap in the range of 0.05-0.4 eV. This value is useful for developing graphene-based electronics, as the carrier mobility of the undoped sheet is not expected to alter.

Organic chemistry of graphene: the Diels-Alder reaction.

Herein, by using dispersion-corrected density functional theory, we investigated the Diels-Alder chemistry of pristine and defective graphene. Three dienes were considered, namely 2,3-dimethoxy-1,3-butadiene (DMBD), 9-methylanthracene (9MA), and 9,10-dimethylanthracene (910DMA). The dienophiles that were assayed were tetracyanoethylene (TCNE) and maleic anhydride (MA). When pristine graphene acted as the dienophile, we found that the cycloaddition products were 47-63 kcal mol(-1) less stable than the reactants, thus making the reaction very difficult. The presence of Stone-Wales translocations, 585 double vacancies, or 555-777 reconstructed double vacancies did not significantly improve the reactivity because the cycloaddition products were still located at higher energy than the reactants. However, for the addition of 910DMA to single vacancies, the product showed comparable stability to the separated reactants, whereas for unsaturated armchair edges the reaction was extremely favorable. With regards the reactions with dienophiles, for TCNE, the cycloaddition product was metastable. In the case of MA, we observed a reaction product that was less stable than the reactants by 50 kcal mol(-1) . For the reactions between graphene as a diene and the dienophiles, we found that the most-promising defects were single vacancies and unsaturated armchair edges, because the other three defects were much-less reactive. Thus, we conclude that the reactions with these above-mentioned dienes may proceed on pristine or defective sheets with heating, despite being endergonic. The same statement also applies to the dienophile maleic anhydride. However, for TCNE, the reaction is only likely to occur onto single vacancies or unsaturated armchair edges. We conclude that the dienophile character of graphene is slightly stronger than its behavior as a diene.