Excited state deactivation mechanisms of protonated adenine: a theoretical study

The quantum chemical computational method and Born-Oppenheimer (BO) dynamics simulation were employed to investigate the non-radiative relaxation mechanism of protonated 9H- and 7H-adenine (AH(+)). We located three conical intersections (CIs) between the first (1)pi pi* excite state and the S-0 ground state potential energy surfaces for the two most stable protonated isomers of adenine. It was predicted that the barrier-free potential energy profile along the out-of-plane deformation coordinates of the six-member ring plays the most prominent role in the deactivation of the excited AH(+) from (1)pi pi* to the ground state via ultrafast internal conversions. This ring deformation was predicted to provide a common deactivation pathway in protonated DNA/RNA bases, describing their high level of photostability, and corresponding neutral homologues.

Automated summary

The non-radiative relaxation mechanism of protonated adenine was investigated using quantum chemical computational methods and dynamics simulations. It was found that the out-of-plane deformation of the six-member ring plays a significant role in the deactivation of the excited state to the ground state, which is important for the photostability of protonated DNA/RNA bases.