A theoretical study on the excited-state deactivation paths for the A-5FU dimer

The photostability of DNA plays a key role in the normal function of organisms. A-5FU is a base pair derivative of the A-T dimer where the methyl group is replaced by a F atom. Here, accurate static TDDFT calculations and non-adiabatic dynamic simulations are used to systematically investigate the excited-state decay paths of the A-5FU dimer related to the proton transfer and the out-of-plane twisting deformation motion of A and 5FU in the (1)pi pi* and (1)n pi* states. CC2 is used to check the accuracy of the current TDDFT calculations. Our results show that the deformation of the C=C or C=N double bond in A and 5FU provides an efficient pathway for the depopulation of the lowest excited states, which can compete with the excited-state proton transfer paths in the dimer. This finding indicates that monomer-like decay paths could be important for the photostability of weakly hydrogen-bonded DNA base pairs and provide a new insight into the excited-state decay paths in base pairs and their analogues.

Automated summary

The study reveals that the deformation of double bonds in A and 5FU can affect the excited-state decay paths of the A-5FU dimer, competing with proton transfer paths and influencing the photostability of DNA base pairs.