Internal conversion and intersystem crossing pathways in UV excited, isolated uracils and their implications in prebiotic chemistry

Abstract

The photodynamic properties of molecules determine their ability to survive in harsh radiation environments. As such, the photostability of heterocyclic aromatic compounds to electromagnetic radiation is expected to have been one of the selection pressures influencing the prebiotic chemistry on early Earth. In the present study, the gas-phase photodynamics of uracil, 5-methyluracil (thymine) and 2-thiouracil -- three heterocyclic compounds thought to be present during this era -- are assessed in the context of their recently proposed intersystem crossing pathways that compete with internal conversion to the ground state. Specifically, time-resolved photoelectron spectroscopy measurements evidence femtosecond to picosecond timescales for relaxation of the singlet 1$\pi \pi$* and 1n$\pi$* states as well as for intersystem crossing to the triplet manifold. Trapping in the excited triplet state and intersystem crossing back to the ground state are investigated as potential factors contributing to the susceptibility of these molecules to ultraviolet photodamage.

arXiv comment21 pages, 5 figures, 1 table

References in corpus (3)

• A singlet and triplet excited-state dynamics study of the keto and enol tautomers of cytosine
• Excitation of Nucleobases from a Computational Perspective II: Dynamics
• Photoelectron Spectra of 2-Thiouracil, 4-Thiouracil and 2,4-Dithiouracil

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• Transient Resonant Auger-Meitner Spectra of Photoexcited Thymine
• Unraveling the relaxation dynamics of Uracil: insights from time-resolved X-ray photoelectron spectroscopy
• State-dependent fragmentation of protonated uracil and uridine