Abstract

Natural DNA and RNA nucleobases are characterized by their photostability upon UV light
continuous exposition. The internal conversion channels, found along the main relaxation
pathways of the five canonical nucleobases, ease the complete deactivation of the monomers
in an ultrafast timescale, preventing the generation of photolesions in the DNA strand1.
Determining the structural and electronic factors that promote these desirable photostable
properties can enormously help to understand the chemical evolution suffered by nucleobases’
ancestors during the prebiotic period to lead in the current genetic alphabet. In this way, the
scrutiny of the deactivation mechanism in modified nucleobases would shed light into the keys
which control the interesting photophysics and photochemistry of these systems.

In this special report, we expose a complete static and dynamics analysis of oxo modified
nucleobases, proposed as nucleobases’ ancestors2, at one of the most sophisticated
multiconfigurational methods, XMS-CASPT23. The molecular dynamics of investigated
systems have showed strong evidences of open-ring photodegradation along their decay routes,
also corroborated by experimental observation4. These unexpected results shedding light on
the effect of functionalization of aromatic rings and establish one of the first examples of
photolabile nucleobase derivate.