To illustrate the power of the strategy, based on a RR analysis by Loppnow we have reconstructed the spectral density for a DNA nucleotide (thymidine 5'monophospate), see Fig. , in water at 298 K and used it to scrutinize its decoherence dynamics. Figure shows the reconstructed spectral density and the overall decoherence dynamics. The parameters used to reconstruct the spectral density are listed in Table of the supplementary information. The spectral density (Fig. ) consists of a broad low-frequency feature (blue line, inset) due to solvent and several sharp peaks due to intramolecular vibrations. The overall decoherence (Fig. , red line) shows an initial Gaussian decay profile, followed by a partial recurrence at ∼ 20 fs and a complete decay of coherence in ∼ 30 fs. The Gaussian feature of the decoherence is a universal feature of initially sepa-rable system-bath states and can be seen as arising due to the quantum Zeno effect. The recurrence signals the partial recovery of the nuclear wavepacket overlap | ⟨χ e (t)| χ g (t)⟩| due to the wavepacket dynamics in the excited state potential energy surface. It is known that this DNA nucleotide also exhibits internal conversion due to the presence of a conical intersection. Such dynamics occurs on time scales of 100s of fs that are significantly longer than those required for the pure dephasing process to complete. This disparity in time scales makes the pure dephasing analysis to remain applicable even in the presence of such non-radiative electronic transitions.