The photocatalysis reaction using [Ru II (bpy)3] 2+ was studied on the example of visible light sensitized Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization. Although both photoinduced electron and energy transfer mechanisms are able to describe this interaction, no definitive experimental proof has been evidenced so far. This paper investigates the actual mechanism governing this reaction. A set of RAFT agents was selected, their redox potentials measured by cyclic voltammetry and relaxed triplet energies calculated by Quantum Mechanics. Gibbs free-energy values were calculated for both electron and energy transfer mechanisms. Quenching rate constants were determined by Laser Flash Photolysis. The results undoubtedly evidence the involvement of a photoinduced energy transfer reaction. Controlled photopolymerization experiments are discussed in light of the primary photochemical process and photodissociation ability of RAFT agent triplet states.