Electronic excited-state dynamics of cytosine and its derivatives studied by time-resolved photoelectron spectroscopy.

Cytosine derivatives, which exist as multiple tautomers in the gas phase, provide an ideal platform to investigate the effects of small structural changes on the photostability of cytosine. To date, most time-resolved spectroscopic studies have been performed in the solution phase where the tautomer ratio is shifted toward the keto form and intersystem crossing dynamics have been associated with an active role of the carbonyl group. Using gas-phase time-resolved photoelectron spectroscopy, this work focuses on the photodynamics of enol and keto cytosine derivatives as well as thionation (thiocytosine), switching of exocyclic groups (isocytosine), and a ring-substitution (azacytosine).