PrdPyr-MeOH structure and energetics in the S 0 state Optimization of the PrdPyr-MeOH geometry in the ground electronic state led to three local minima: PPMet-1, PPMet-6, and PPMet-4, whose structures and zero-point (ZPE) corrected relative energies are shown in Figure . In all cases, the MeOH molecule acts as a proton donor in a single hydrogen bond (HB) formed with one of nitrogen atoms of the PrdPyr moiety. In Table , one can find selected geometrical parameters of the obtained structures. Upon inspection, a similar N-H distance (i.e., the HB length) of ca. 2.0 Å is noticed in all three conformers, which falls into a range characteristic for medium-strength HBs in organic systems. Interestingly, the MeOH molecule orients itself (the CONC dihedral angle) with different level of perpendicularity with respect to the PrdPyr plane, which is likely driven by interplay between steric repulsion between PrdPyr and the methyl group, and the attractive interaction between the methyl hydrogens and the adjacent electronegative center. This orientation directly impacts the electronic coupling between the proton-donor molecule and the protonacceptor moiety, making an important difference as compared to analogous water complexes formed with multi-center, electron-rich organic molecules, in which the water molecule usually adopts an allplanar orientation. For the complete data on the S 0 PrdPyr-MeOH molecular structures, please refer to Cartesian coordinates included in the Electronic Supplementary Information (ESI).