Photo protection of RNA building blocks: Adenosine 5′-monophosphate, cytidine 5′-monophosphate and cytosine

Photoprotection of the RNA nucleotides adenosine 5′-monophosphate and cytidine 5′-monophosphate, and the nucleobase cytosine was studied using UV pump, IR probe femtosecond transient absorption spectroscopy. The excitation energy is contained in the aromatic ring system, protecting the RNA backbone. All three molecules dissipate the excitation energy by internal conversion and subsequent vibrational relaxation to the electronic ground state in less than 10 ps. In addition, a second deactivation channel is found in cytidine 5′-monophosphate, illustrated by a signal at 1563 cm−1 with a lifetime of 33 ps assigned to an nπ∗ state in agreement with observations in the UV region.