The excited state deactivation mechanism of 8-Vinylguanine: Competition between fluorescence and nonadiabatic process

The stable inheritance of genetic information in DNA and RNA relies critically on the exceptional photostability of nucleobases, which rapidly dissipate absorbed UV energy through ultrafast nonradiative pathways. Modifying nucleobases offers a powerful strategy for tuning their photophysical and photochemical properties. 8-Vinylguanine (8vG), a guanine analogue featuring a vinyl substitution at the C8 position, exhibits intense fluorescence upon photoexcitation, distinguishing it from the natural guanine. In this work, we investigate the complex deactivation mechanism of 8vG in its excited state by combining high-level electronic structure calculations with excited-state on-the-fly surface hopping nonadiabatic dynamics simulations. Our results show that nonradiative decay primarily occurs through a ring puckering motion within the guanine moiety, directly competing with fluorescence emission. Consequently, 8vG exhibits a significantly prolonged excited-state lifetime compared to unmodified guanine. This study provides a detailed mechanistic understanding of the competition between fluorescence and nonradiative decay in 8vG, offering fundamental insights for the rational design of bio-inspired photostable systems or fluorescent probes with tunable properties.