Supporting Information for Trifluoromethylation of Graphene Figure S1. Raman spectrum of pristine graphene and the same graphene sample after immersing in a solution of 30 mM Togni reagent in anhydrous methanol under the protection of argon gas. Figure S2. Raman spectrum of the trifluoromethylated graphene shown in Figure 2c. Figure S3. (a) High-resolution I 3d spectrum of the same region on the trifluoromethylated graphene. The absence of I 3d peaks indicates that iodine element does not exist in this area. (b) The low resolution XPS survey of the same trifluoromethylated graphene supported by 300 nm SiO2 substrate, in which the Si, and O peaks come from the SiO2 substrate. Thus, contaminations on graphene such as CuCl, Togni can be excluded. Figure S4. Raman spectra of graphene samples with different degree of trifluoromethylation. The black, blue and red curves correspond to the same sample shown in figure 4a. Theoretical part: To investigate the structure and properties of trifluoromethylated graphene, density functional theory (DFT) calculations using the Vienna ab initio simulation package (VASP) within the local density approximation (LDA) were performed on the adsorption of CF3 groups on graphene with various coverages and arrangements. We first simulated the adsorption configurations of two CF3 groups on 50 carbon atoms, since the experimental coverage is nearly 4% deduced from the XPS result. Three representative configurations are shown in Figure S6a. For two CF3 groups at para sites in a hexagonal ring, the short distance between CF3 leads to repulsive force, and increases the total energy to -0.22 eV. As the distance increases, the repulsive force between CF3 groups decreases. The energetically favorable configure for this coverage is shown in the right plane of Figure S6a, which corresponds to the uniform distribution of CF3 groups on graphene (Eb = -0.54 eV, Eb=binding energy). Since CF3 groups prefer to uniformly adsorb on graphene, the binding energy per CF3 group for the uniform configurations for various coverage were calculated (Figure S6b). The binding energy is largest for the 4% coverage (C50(CF3)2), which is consistent with the CF3 coverage observed in experiment. The band structure of this stable configuration is shown in figure S6c. Interestingly, a band gap as large as 1.2 eV is expected to open up after trifluoromethylation. Figure S5. (a) Adsorption of a CF3 dimer on graphene. (b) Calculated binding energy of different CF3 adsorption configurations. (c) Band structure for homogeneous CF3 adsorption pattern on graphene (C50(CF3)2).