We have investigated, by density functional theory calculations (DFT), the preferential substitution of the para-position considering a reduced model of the Cu@f-gC3N4 photocatalyst made of two melamine subunits, a fluorinated ligand, and a single coordinated Cu atom. Previous studies and electron paramagnetic resonance (EPR) characterizations have indicated that this model accurately represents the heightened catalytic activity of the material . This enhancement primarily arises from the entrapment of the Cu atom between two pyridinic nitrogen of the f-gC3N4 rings, the presence of the adjacent ligand (Figure , see in ESI), which determines an optimal d-band position for the catalyst, the system's absorption in the blue region of the spectrum, and the direct adsorption of the reactant onto the metal center through a C-C bond on the ring. Subsequently, the photocatalyst activates the para-C-H bond of the arene complex due to the adopted preferential binding mode of the benzene ring. This observation aligns well with existing literature .