Theoretical study on the sequential hydroxylation of C82 fullerene based on Fukui function

In the present work semi-empirical PM3 method and ab initio density-functional theory calculations were performed in carbon systems. The condensed Fukui function was calculated and HOMO-LUMO were visualised in order to study the sequence of hydroxylation of two isomers of C-82 fullerene for the low coverage regime, with the formula C-82(OH)(x) where x = 0 - 12. It was found that there was a formation of dangling bonds on structures with an odd number of hydroxyl groups on the fullerene surface, which suggests an enhanced reactivity of these molecules. Nevertheless, the coverings with an even number of groups tend to the reconstruction of pi bonds, obtaining less reactive molecular structures. With the adsorption of the first group, a narrow HOMO-LUMO gap (1.28 eV) is observed in comparison with the C-82(OH)(2) system (1.70 eV), as is found in similar systems, such as C-60 fullerenol [E. E. Fileti et al., Nanotechnology 19, 365703 (2008); J.G. Rodriguez-Zavala and R. A. Guirado-Lopez, Phys. Rev. B 69, 075411 (2004)]. Through an analysis of the electronic structure to these coverings, a splitting of electronic energy levels in the structure with one hydroxyl group is observed, which could be one of the factors that causes the narrowing of the energy gap in this structure. On the other hand, with a coverage of 12 hydroxyl groups, the formation of an amphiphilic molecule, where the location of groups in one side of the C-82 surface provides an hydrophilic character, is observed, while the uncovered part has an hydrophobic character. This could be important in the formation of Langmuir monolayers. Finally, it is shown that the precise distribution of the OH groups on the fullerene surface plays a crucial role in the electronic structure of the polyhydroxylated fullerenes.