In contrast to the 7H tautomer, the photodeactivation of 9H 2,6-dAP from its lowest energy singlet excited state is governed by puckering of the 6-membered subunit of the aromatic purine ring. In particular, the S 1 (ππ*) minimum of 9H 2,6-dAP is characterized by pyramidalization of the C 2 atom. From the S 1 minimum, the experimental results indicate the existence of two possible relaxation pathways with a faster internal conversion through a S 1 /S 0 CI corresponding to the ps decay component competing with a slower pathway corresponding to the ns decay component. The extent of this pyramidalization and aromatic ring puckering is increased when the molecule approaches the S 1 (ππ*)/S 0 conical intersection (see Fig. ). This state crossing lies nearly 0.4 eV higher in energy than the corresponding S 1 (ππ*) minimum and explains the long photodeactivation time constant, which amounts to 6.3 ns. We emphasize that owing to a relatively high oscillator strength of the S 1 -S 0 transition from the S 1 (ππ*) minimum, this time constant could indeed be associated with fluorescence when the 9H tautomer is excited at the absorption origin. Alternatively, UV-excited 9H 2,6-dAP could undergo a change in the puckering mode associated with substantial rotation of the C 6 -NH 2 amino group out of the plane of the aromatic purine ring and reach another ring-puckered S 1 (ππ*)/S 0 conical intersection (see Fig. ). While this latter process is associated with an energy barrier of merely 0.1 eV, it also requires fitting of a picosecond excited-state decay component for the 9H tautomer.