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Denis P.A.,Computational Nanotechnology
Journal of Physical Chemistry C | Year: 2013

The chemical reactivity of electron-doped and hole-doped graphene was studied by means of first principles calculations, on the basis of dispersion corrected density functional theory. To model hole-doped graphene, the widely known electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) was utilized, while the electron donor tetrathiafulvalene (TTF) was selected for the electron-doped case. The results demonstrate that the reactivity of graphene can be modified by the adsorption of electron donating/withdrawing molecules. The reactions considered were the addition of fluorine atoms and hydroxyl radicals. In both cases, it was observed that the adsorption of F4-TCNQ and TTF increased the reactivity of graphene. This outcome was expected for electron-doped graphene because we have recently shown that lithium increases the reactivity of graphene. Yet, for F4-TCNQ, the finding is surprising given that this molecule accepts 0.4 e- from graphene. The gas phase free energies of association are calculated to be negative for F4-TCNQ and TTF, but for the latter is only -2.5 kcal/mol. The results obtained employing infinite models and using the VDW-DF and M06-L functionals are supported by cluster model calculations performed with the M06-2X method. When TTF was adsorbed onto graphene, a charge transfer from TTF to graphene was not observed. However, when TTF and F4-TCNQ are simultaneously adsorbed on opposite sides of the graphene sheet, the amount of charge accepted by F4-TCNQ and donated by TTF is increased. This work clearly suggests that dual doping is a useful tool to expand, even to a greater extent, the possibilities to tune the properties of graphene. Further work must be devoted to synthesize better electron donors and acceptors and thus allow for larger charge transfer. © 2013 American Chemical Society. Source

Denis P.A.,Computational Nanotechnology
RSC Advances | Year: 2013

We have studied the ability of 26 receptors to catch the fullerenes C 60 and C70. The prediction of which host displays the largest affinity with fullerenes is complicated by the fact that some hosts are extremely flexible. For example, the cyclotriveratrylene (CTV) based host, with three 2-[9-(1,3-dithiol-2-ylidene)anthracen-10(9H)-ylidene]-1,3-dithiole (exTTF) pincers, has an interaction energy that is quite modest and even lower than that determined for the famous C60H28 buckycatcher. Notwithstanding this energetic difference, experimental results indicated that the exTTF-CTV host has an association constant comparable to those reported for metalloporphyrins. In line with the recent experimental results we found that when three corannulene pincers are attached to cyclotriveratrylene, the ability of the host to interact with fullerene is not improved with respect to the C60H28 buckycatcher, which has two corannulene pincers. Our theoretical calculations showed that the reason for such an outcome is that the corannulene pincers are stacked and thus a large amount of energy is required to break the intramolecular dispersion interactions that keep the structure stacked. A similar scenario was found when we attached one, two and three exTTF pincers to pentakis(1,4-benzodithiino)corannulene. Bearing these results in mind, and considering that the C60H28 buckycatcher is somewhat rigid, we alkylated the rim of the corannulene pincers. The alkylated buckycatcher is able to interact with C60 with an interaction energy that is larger than that corresponding to the unsubstituted host. Therefore, functionalization of the C60H28 buckycatcher seems to be the most promising road to the synthesis of new fullerene receptors that are not based on metalloporphyrins. The design of new hosts must be pursued with the aim of finding receptors whose most stable conformations are similar to that expected in the supramolecular complex. This journal is © The Royal Society of Chemistry. Source

Denis P.A.,Computational Nanotechnology
Computational Materials Science | Year: 2013

First principle calculations were applied to study the electronic properties of S and P-doped graphene. In particular, the PBE and HSE06 density functionals were utilized. The comparison of the band gaps obtained with both functionals indicated that the band gaps at the PBE level are only slightly smaller than those obtained with HSE06. Specifically, the deviation variation was much smaller than that observed for carbon nanotubes or graphane. Phosphorus doping is somewhat more effective in opening larger optical gaps. The latter decreases very fast, upon lowering of dopant concentration. In the case of S-doping, for a doping concentration smaller than 0.5 at.%, the gaps are close to 0.1-0.2 eV, making the material not too attractive to develop graphene based electronics. However, for phosphorus doping, a dopant concentration of 0.5% is still useful as band gaps close to 0.3-0.4 eV are expected. Further work must be devoted to obtain larger band gaps by doping graphene with heteroatoms, which are necessary to develop graphene based electronics. © 2011 Elsevier B.V. All rights reserved. Source

Denis P.A.,Computational Nanotechnology
Chemical Physics Letters | Year: 2014

Herein, we studied the interaction between the fullerenes C60 and C70 with pentaindenocorannulene (P), chrysaorole (C) and two new buckycatchers. The P and C bowls interact with the fullerenes with an interaction-energy (IE) that is twice the value determined for corannulene. The new receptors designed include a cyclooctatetraene core which has two P or C pincers attached. Notwithstanding the fact that the proposed hosts prefer stacked conformations at equilibrium, the IE determined are extremely large and close to the ones computed for the dimeric metalloporphyrins. It is our hope that this work stimulates the synthesis of these receptors. © 2013 Elsevier B.V. All rights reserved. Source

Denis P.A.,Computational Nanotechnology | Iribarne F.,Laboratorio Of Bioinformatica Y Farmacologia Molecular
Chemistry - A European Journal | Year: 2012

The interaction between alkyl radicals and graphene was studied by means of dispersion-corrected density functional theory. The results indicate that isolated alkyl radicals are not likely to be attached onto perfect graphene. It was found that the covalent binding energies are low, and because of the large entropic contribution, ΔG° 298 is positive for methyl, ethyl, isopropyl, and tert-butyl radicals. Although the alkylation may proceed by moderate heating, the desorption barriers are low. For the removal of the methyl and tert-butyl radicals covalently bonded to graphene, 15.3 and 2.4 kcal mol -1 are needed, respectively. When alkyl radicals are agglomerated, the binding energies are increased. For the addition in the ortho position and on opposite sides of the sheet, the graphene-CH 3 binding energy is increased by 20 kcal mol -1, whereas for the para addition on the same side of the sheet, the increment is 9.4 kcal mol -1. In both cases, the agglomeration turns the ΔG° 298<0. For the ethyl radical, the ortho addition on opposite sides of the sheet has a negative ΔG° 298, whereas for isopropyl and tert-butyl radicals the reactions are endergonic. The attachment of the four alkyl radicals under consideration onto the zigzag edges is exergonic. The noncovalent adsorption energies computed for ethyl, isopropyl, and tert-butyl radicals are significantly larger than the graphene-alkyl-radical covalent binding energies. Thus, physisorption is favored over chemisorption. As for the ΔG° 298 for the adsorption of isolated alkyl radicals, only the tert-butyl radical is likely to be exergonic. For the phenalenyl radical we were not able to locate a local minimum for the chemisorbed structure since it moves to the physisorbed structure. An important conclusion of this work is that the consideration of entropic effects is essential to investigate the interaction between graphene and free radicals. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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