Understanding How a New Hachimoji Nucleobase Alters Photodynamics of Genetic Building Blocks † .

This article is a highlight of the paper by Krul et al. in this issue of Photochemistry and Photobiology. It describes the excited state dynamics of 5-aza-7-deazaguanine ( 5N7C G), which has recently been proposed as an alternative nucleobase. Upon UV absorption to the lowest energy 1 ππ* state, 5N7C G returns to the electronic ground state an order of magnitude more slowly than guanine with a corresponding greater fluorescence quantum yield. These findings are significant because they suggest that 5N7C G is less UV photostable than its canonical nucleobase equivalent, which would have been a selective disadvantage in prebiotic conditions.