The estimated energy barrier DE ‡ was about 16 kcal/mol. After demonstrating that the LED light induced the adsorption of -CF3 on the para site, we estimated the energy of the intermediate complexes (obtained after the first excitation) of other species where the NO2 moiety was replaced with the -CF3, -CN, and -OCH3 groups (Table , ESI). In these optimized complexes, the arenes adopted similar binding modes and were all prone to accept the -CF3 moiety in the para position (Table , ESI). An estimate of the reactant and transition structures (where the ring H was transferred to the catalyst) energies also confirmed in these cases the para preference (Table , ESI).