All the calculations were first carried out on the nitrobenzene reactant to reproduce all the steps of the mechanism leading to the final products. The optimized configuration of the catalyst-reactant complex resulted in an almost stacked geometry of the nitrobenzene and melamine unit, with the nitrobenzene molecule directly connected to the Cu(I) atom through an aromatic Cortho-Cmeta bond of the ring, which slightly elongated from 1.39 to 1.41 Å (37). This proposed η 2 -benzene bonding was also obtained in all the substituted species examined in this work and confirmed by previous X-ray crystallography studies for other systems . The coordination of Cu to the ring nitrogen was found at similar, slightly shorter distances of about 2.06 Å. Instead, the preferential location of the -NO2 group (and the other substituents of the considered adsorbed species) was in the region of the photocatalyst's ligand but inclined towards the opposite direction to minimize unfavorable interactions (similar MEP zones). The NBO analysis helped to interpret the system's charge distribution to disclose the arene ring's activation mechanism. Before the adsorption of nitrobenzene, the Cu-cation was trapped between the nitrogen of two opposite triazine rings had a charge of approximately +0.85. Still, after the adsorption of the molecule, Cu showed a reduced net charge of roughly +0.74, whereas the LIGf-gC3N4 system (photocatalyst) and nitrobenzene had -0.40 and -0.34 charges, respectively. This suggested that the electron density flowed from the photocatalyst (mainly the ligand -Figure red regions, see in ESI) to the adsorbed nitrobenzene-Cu orbitals, and the para-C-H bond (with a total charge of +0.11 compared to the -0.04 charge of the meta positions) was found more prone to accept the vacant radical anion CF3 moiety placed nearby (Figure ). Besides rationalizing a more probable para substitution by looking at the local NBO charges, we resorted to the visualization of the molecular electrostatic potential maps projected onto the corresponding oneelectron densities at the level of the theory mentioned above to confirm the adsorption scenario. As shown in Figure (see in ESI), the MEP of nitrobenzene is positive everywhere above the aryl plane and negative in the regions of the oxygen/nitrogen lone pairs (and fluorines), indicating that both the catalyst ligand and the -NO2 moiety are relatively strong inductive electronwithdrawing groups. The MEPs of the complexes, with and without (Figure ) the -CF3 group placed on top of nitrobenzene, show a redistribution of the charges (thus slightly different MEP areas) and reveal that the para-C-H site was less hindered and more complementary to the approaching species.