Disentangling Complex UV-Induced Relaxation Dynamics of 2′-Deoxyadenosine from 30 fs to 10 ps

We characterize the photoactivated processes in 2'-deoxyadenosine (dA) in aqueous solution by combining transient absorption spectroscopy with 30 fs resolution, quantum mechanical calculations, and quantum dynamical simulations. Using TD-DFT within a polarized continuum model, we map the lowest-lying excited states - two ππ* (La and Lb) and one nπ* (Sn) - identifying five low-energy basins and computing their absorption spectra. Nonadiabatic transitions among them are described through quantum dynamics propagations. The evolution of the experimental photoinduced bands is rationalized through comparison with computed spectra, avoiding global multiexponential fits, incompatible with the evolving electronic structure of the chromophore. The first 100 fs are governed by the Lb - La interplay. Subsequently, the wave packet undergoes nonradiative decay to the ground state or explores the nonplanar region of the La surface, whose lifetime is 470 fs. Sn is the longest living excited state, decaying with a time constant of 1 ps.