Therefore, we performed single point calculations at the NEVPT2/SA-CASSCF/def2-TZVP level to validate the potential energy profiles obtained with the SCS-ADC(2) method. As presented in Fig. , the SCS-ADC(2) results are in excellent qualitative agreement with the NEVPT2 energies and the primary quantitative difference between the two datasets is associated with a systematic shift of the PE profile obtained with the NEVPT2 approach to higher energies. Furthermore, the positions and geometries of the S 1 /S 0 conical intersections were correctly identified with the SCS-ADC(2)/SCS-MP2 approach. Consequently, the S 1 /S 0 conical intersection associated with the puckering of the 5-membered subunit of the purine aromatic ring of 7H 2,6-dAP is a possible photorelaxation mechanism, which was not identified in the previous study by Oliveira et al. Further, we have corroborated their finding of the C6-puckering mechanism for 7H 2,6-dAP. We located a virtually identical geometry of the C6-puckered S 1 /S 0 MECP of 7H 2,6-dAP at the SCS-ADC(2)/SCS-MP2 level, and the associated potential energy profile exhibits an analogous high energy barrier (of 0.8 eV above the S 1 minimum) exceeding the vertical excitation energy of the S 1 state. It is worth noting though that we were not able to identify the S 1 minimum of 9H 2,6-dAP having the mostly planar geometry of the purine ring and the C6-NH2 group tilted by merely 28°with the SCS-ADC(2) method. We argue that SCS-ADC(2) likely overestimates the steepness of the S1 PE surface of 9H 2,6-dAP along the C6-puckering coordinate. Indeed, the corresponding NEVPT2 energies suggest a much flatter topography of this S 1 PE surface in the vicinity of the Frank-Condon region, which is indicative of the presence of another S 1 minimum which cannot be reproduced at the SCS-ADC(2) level. At the same time, the NEVPT2 results corroborate the feasibility of the ballistic C6-puckering mechanism of 9H 2,6-dAP, which can bypass this minimum and result in ultrafast photodeactivation as presented in Fig. . In other words, the C6-puckered S 1 /S 0 conical intersection of 9H 2,6-dAP can be reached in a barrierless manner from the Franck Condon region.