Comparison of the dynamics of 2,6-dAP, purine, adenine, 2AP, and guanine shows a complex dependence on structure. Purine, the base structure, has a long excited state lifetime due to significant ISC . Addition of a single amino group to C 6 forms adenine (6-aminopurine) with ultrafast nonradiative decay via 1 ππ* → 1 nπ* → S 0 and without any measurable triplet yield . Adding an amino group to purine at C 2 forms 2AP with slower relaxation than adenine . 2AP also yields a sizable triplet population in the gas phase and in nonpolar solvent. This juxtaposition has suggested that the substitution of C 2 determines photostability . However, in 2AP, adding an oxo group to C 6 forms guanine, which leads to ultrafast nonradiative decay via a 1 ππ*/S 0 conical intersection. . Switching the oxo group on C 6 of guanine with an amino group leads to 2,6-dAP, which in the 9H form we found to follow the same path as guanine . In the 7H form 2,6-dAP further has a triplet yield, in similar fashion as 2-oxopurine. Even though 2,6-dAP shares structural elements with both 2AP and adenine, it does not have the same dynamics as either. 2,6-dAP is also the least photostable of these purines with the possible exception of purine itself. Photodynamics is intricately tied to structure, not only for ligand substitution, but also for tautomerization . With some data points in the purine structural family still missing, these results help shed light on the almost unique photostability of the canonical nucleobases and will hopefully lead to a more mechanistic understanding of the subtle interplay between structure and excited state dynamics.