Strong N-Doped Graphene: The Case of 4-(1,3-Dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine (N-DMBI)

By means of first principle calculations, we investigated the effects of the adsorption of the strong n-type dopant 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine (N-DMBI) onto graphene. The adsorption of radical N-DMBI (R-N-DMBI) occurs with large adsorption energy (E-ads) of 44.4 kcal/mol and induces a metallic character on graphene by shifting the Dirac point 0.6 eV below the Fermi level. The charge received by graphene can be almost completely removed and thus the metallic character may be inhibited if 2,3,5,6-tetrafluoro-7,7,8,8-tetra-cyanoquinodimethane (F4-TCNQ) is simultaneously adsorbed on any side of graphene. In effect, by doing so, the semimetallic character is recovered or a tiny gap is opened. When F4-TCNQ and radical N-DMBI are adsorbed on the same side, the molecules are strongly held together thanks to the hydrogen bond formed between the fluorine atoms of F4-TCNQ and the H of R-N-DMBI. In this case, the E-ads is over 120 kcal/mol, per F4-TCNQ/R-N-DMBI pair. When the latter two molecules are adsorbed on opposite sides, the E-ads is 87.6 kcal/mol. This value is more than 30 kcal/mol smaller than that computed when they are adsorbed on the same side, even though it is nearly 10 kcal/mol larger than the sum of the E-ads of isolated F4-TCNQ and R-N-DMBI. In this case, graphene behaves as a medium that transfers electrons from R-N-DMBI to F4-TCNQ, without having the molecules in direct contact. We see a strong synergic interaction that increases the E-ads when an electron donating molecule is combined with an electron withdrawing one. R-N-DMBI has a profound influence on the reactivity of graphene. Bond energies between the graphene surface and H, F, and OH radicals increased when R-N-DMBI is adsorbed, but the addition of these radicals destroys the metallic character of the graphene-R-N-DMBI complex and band gaps in the range of 0.2-0.4 eV are opened. These results show that the radical N-DMBI alters the chemistry and electronic properties of graphene to an extent, which rivals the most popular molecules and substrates used in the noncovalent chemistry of graphene.