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Excited State Dynamics of Isocytosine; a Hybrid Case of Canonical Nucleobase Photodynamics

Authors: 
Jacob Berenbeim, Samuel Boldissar, Faady Siouri, Gregory Gate, Michael R. Haggmark, Briana Aboulache, Trevor Cohen, Mattanjah de Vries
Journal Name: 
The Journal of Physical Chemistry Letter
Volume: 
8
Issue: 
20
Pages From: 
5184
To: 
5189
Date: 
Friday, October 6, 2017
Abstract: 
We present resonant two-photon ionization (R2PI) spectra of isocytosine (isoC) and pump–probe results on two of its tautomers. IsoC is one of a handful of alternative bases that have been proposed in scenarios of prebiotic chemistry. It is structurally similar to both cytosine (C) and guanine (G). We compare the excited-state dynamics with the Watson–Crick (WC) C and G tautomeric forms. These results suggest that the excited-state dynamics of WC form of G may primarily depend on the heterocyclic substructure of the pyrimidine moiety, which is chemically identical to isoC. For WC isoC we find a single excited-state decay with a rate of ∼1010 s–1, while the enol form has multiple decay rates, the fastest of which is 7 times slower than for WC isoC. The excited-state dynamics of isoC exhibits striking similarities with that of G, more so than with the photodynamics of C.