The first perfluoroalkylation reaction of activated arenes (amino-substituted arenes and alkoxyarenes) has been achieved in water by employing the dyad Rose Bengal and hydrosoluble unmodified vitamin B₁₂ (cyanocobalamin) as the photocatalyst and co-catalyst, respectively. The reaction was performed under green LED irradiation and employed perfluoroalkyl bromides as the perfluoroalkyl radical sources. In particular, the presence of vitamin B₁₂ co-catalyst was found to be fundamental to elicit the formation of perfluoroalkyl radicals.