Taking into account the local excitation character of the identified S 2 and S 1 minima (with the exception of the S 1 state of PPMet-4), in the next step, we calculated relaxed adiabatic reaction profiles along the proton-transfer coordinate, i.e., the O-H distance, in the S 1 state. For the PPMet-1 and PPMet-6 complexes, the O-H bond length was the only parameter kept fixed, while for the PPMet-4 isomer a more complex approach was undertaken, to prevent the immediate S 1 → S 0 degeneration due to the PCET process. Namely, in the latter case, two different paths were calculated: (i) one following the PT reaction but with the ON 4 N 6 angle fixed at its S 0 -optimized value for O-H distances shorter than 1.20 Å (the direct path), and (ii) a two-part sequential scan, including, firstly, an OH-fixed scan along the descending O-N 6 distance and, secondly, the O-H bond elongation from the final obtained structure (the indirect path). Results of these scans are presented in Figure .