Unveiling the Ring-Deformation-Driven Photostability of Isolated G-C Base Pair: A Caspt2//Casscf and Nonadiabatic Dynamics Perspective

Abstract

The photostability of DNA and RNA, critical for maintaining genetic integrity, is closely tied to ultrafast nonradiative decay mechanisms that dissipate excess electronic energy. Using CASSCF//CASPT2 calculations and nonadiabatic dynamics simulations, we show that ring puckering enables rapid sub-300 fs internal conversion in the Watson-Crick guanine-cytosine (G-C) base pair. These findings challenge the traditional proton-transfer-centric model and establish structural flexibility, particularly ring distortion, as a universal photostability determinant in nucleobases.

Keywords: nonadiabatic, ring-puckering, decay mechanism, internal conversion