In order to have a more complete view of the nonadiabatic S 1 /S 0 interaction during the EDPT process, we performed an XMS-CASPT2 optimization of the minimum-energy conical intersection (MECI) points in all complexes. The resulting structures and their relative energies calculated with respect to the corresponding S 0 minima are shown in Figure . One can notice that all identified MECIs represent EDPT structures: in all cases, the proton is fully transferred to the PrdPyr moiety, with the universal N-H bond length of ca. 1.025 Å, and the O-H distances of 1.865 Å (PPMet-4), 1.964 Å (PPMet-6), and 2.000 Å (PPMet-1). To provide most accurate comparison between MECI points obtained in the multi-reference calculations, and the interstate crossing points determined at the ADC(2) level, we performed additional MECI optimization employing the penalty functional method combined with ADC(2): results of these calculations are shown in Fig. in the ESI. MECIs determined with the penalty-functional method lie very close to S 1 /S 0 crossing points at the adiabatic scans reported in Fig. . Moreover, a connection between the ADC(2) and the corresponding data from the XMS-CASPT2 calculations can be observed, with systematic energy-up-shift of ca. 0.6 eV, and with elongation of the O-H bond length of 0.50 Å in the latter case. At the same time, the order of the PPMet isomers with respect to the O-H distances at the MECI points is consistent between both approaches. It should be also noted that the MECI energy rise is accompanied by a similar upshift of the S 0 → S 1 excitation energy at each isomer's Franck-Condon region. More details regarding the discussed MECI calculations, including visualization of employed molecular orbital active spaces, can be found in the ESI (Fig. and Table ).