To complete the static analysis in Figure we also report the relaxed scan profile detailing the PES along the Hydrogen transfer coordinate. Interestingly, while most of the triplet states and S2 presents a barrier, which can reach up to 0.2/0.3 eV, the process is barrierless on the S1 surface. Hence, the population of the pp* excited state should certainly be connected with the weakening of the OH bond, and the strengthening of the complementary H-bond, leading to the effective transfer.