The Effect of A-DNA and B-DNA Conformation on the Interplay between Local Excitations and Charge-Transfer States in the Ultrafast Decay of Guanine-Cytosine Stacked Dimers: A Quantum Dynamical Investigation

We here simulate in the gas phase the population dynamics of guanine/cytosine (GC) and cytosine/guanine (CG) stacked dimer in B-DNA and A-DNA arrangement,following excitation in the lowest energy band, and considering the four lowest energy ππ∗ bright excited states, the three lowest energy nπ∗ states, and the G→CCharge Transfer (CT) state. We resort to a generalized Linear Vibronic Coupling model (LVC) parameterized with time-dependent density functional theory computations(TD-DFT), exploiting a fragment based diabatization and we run nonadiabatic quantum dynamical simulations with the multilayer-version of the MulticofigurationalTime Dependent Hartree (ML-MCTDH) approach. G→C CT results a major decay process for GC in B-DNA, but less in A-DNA arrangement, where also the populationtransfer to the lowest energy excited state localized on C is an important inter-monomer process. In CG arrangements mostly intra-monomeric decays take place. We simulate the dynamics of several other GC structures, whose arrangement is intermediate between B-DNA and A-DNA, obtaining further insights on the effect that the sequence and, especially, the stacking geometry have on the population transfer to the G→C CT.