Denis Pablo A
Computational Nanotechnology, DETEMA, Facultad de Química, UDELAR, CC 1157, 11800 Montevideo (Uruguay), Fax: (+589) 229241906.
Chemphyschem. 2013 Oct 7;14(14):3271-7. doi: 10.1002/cphc.201300533. Epub 2013 Aug 9.
Dispersion-corrected density functional theory is utilized to study the addition of aryl radicals to perfect and defective graphene. Although the perfect sheet shows a low reactivity against aryl diazonium salts, the agglomeration of these groups and the addition onto defect sites improves the feasibility of the reaction by increasing binding energies per aryl group up to 27 kcal mol(-1). It is found that if a single phenyl radical interacts with graphene, the covalent and noncovalent additions have similar binding energies, but in the particular case of the nitrophenyl group, the adsorption is stronger than the chemisorption. The single vacancy shows the largest reactivity, increasing the binding energy per aryl group by about 80 kcal mol(-1). The zigzag edge ranks second, enhancing the reactivity 5.4 times with respect to the perfect sheet. The less reactive defect site is the Stone-Wales type, but even in this case the addition of an isolated aryl radical is exergonic. The arylation process is favored if the groups are attached nearby and on different sublattices. This is particularly true for the ortho and para positions. However, the enhancement of the binding energies decreases quickly if the distance between the two aryl radicals is increased, thereby making the addition on the perfect sheet difficult. A bandgap of 1-2 eV can be opened on functionalization of the graphene sheets with aryl radicals, but for certain configurations the sheet can maintain its semimetallic character even if there is one aryl radical per eight carbon atoms. At the highest level of functionalization achieved, that is, one aryl group per five carbon atoms, the bandgap is 1.9 eV. Regarding the effect of using aryl groups with different substituents, it is found that they all induce the same bandgap and thus the presence of NO(2), H, or Br is not relevant for the alteration of the electronic properties. Finally, it is observed that the presence of tetrafluoroborate can induce metallic character in graphene.
采用色散校正密度泛函理论研究芳基自由基与完美及有缺陷石墨烯的加成反应。尽管完美石墨烯片对芳基重氮盐显示出低反应活性，但这些基团的聚集以及在缺陷位点上的加成通过将每个芳基的结合能提高至27 kcal mol⁻¹，提高了反应的可行性。研究发现，如果单个苯基自由基与石墨烯相互作用，共价加成和非共价加成具有相似的结合能，但在硝基苯基的特定情况下，吸附作用强于化学吸附。单空位显示出最大的反应活性，使每个芳基的结合能增加约80 kcal mol⁻¹。锯齿形边缘排名第二，相对于完美石墨烯片，反应活性提高了5.4倍。反应活性较低的缺陷位点是斯通-威尔士型，但即使在这种情况下，孤立芳基自由基的加成也是放能的。如果基团连接在附近且位于不同的子晶格上，则芳基化过程更有利。对于邻位和对位尤其如此。然而，如果两个芳基自由基之间的距离增加，结合能的增强会迅速降低，从而使在完美石墨烯片上的加成变得困难。用芳基自由基对石墨烯片进行功能化时可打开1-2 eV的带隙，但对于某些构型，即使每八个碳原子有一个芳基自由基，该片仍可保持其半金属特性。在实现的最高功能化水平下，即每五个碳原子有一个芳基，带隙为1.9 eV。关于使用不同取代基的芳基的影响，发现它们都诱导相同的带隙，因此NO₂、H或Br的存在与电子性质的改变无关。最后，观察到四氟硼酸盐的存在可在石墨烯中诱导金属特性。
