The direct relaxed scans, shown in the upper panel of Figure , illustrate the general photorection mechanism of PrdPyr-MeOH. After the initial S 0 → S 2 excitation and the subsequent ultrafast internal conversion to the S 1 state, the system is likely to reach energy minimum of the S 1 surface, with the O-H bond length almost unchanged with respect to its ground-state equilibrium value. The barrier separating the minimum from a downhill PT reaction exhibits similar height for all three isomers (about 0.1 eV for PPMet-6 and 0.2 eV for PPMet-1 and PPMet-4). However, its position, that is the necessary O-H elongation to move past the barrier, gradually shifts away from the Franck-Condon region in the PPMet-6 → PPMet-4 → PPMet-1 sequence. This shift could translate to a kinetic effect, enhancing the relaxation mechanism requiring the least distorted geometry. Additionally, at the barrier a change of the character of the S1 state occurs. The oxygen lone-pair alignment with the aromatic π orbitals at the PrdPyr fragment changes after crossing the barrier, resembling more the orientation observed in the Franck-Condon region for the S 0 → S 5 transition, with strongly enhanced charge-transfer character (see Fig. and Table in the ESI for the NTOs plots and CT coefficients calculated along the PT path). This change, accompanied by weak, yet observable interaction between the oxygen and the neighbouring-N atom (i.e., the N atom not participating in the HB formation) lone electronic pairs, is expected to facilitate the intermolecular electron transfer process.