UV-light exposure on DNA has been thoroughly studied over the past two decades as it has been shown to prompt the first molecular motions leading to growing healthcare concerns like skin cancer melanoma. Absorption in DNA triggers complex excited state dynamics with overlapping features in time and wavelength on standard 1D-pump-probe set-ups, hampering their characterisation. The recent emergence of two-dimensional electronic spectroscopy (2DES) opens new possibilities for monitoring such photoreactions with unprecedented accuracy, as these techniques contain a wealth of information associated to both peak position and overall shape of the signals registered. The intricate nature of these experiments often requires theoretical models for their proper characterisation, highlighting how important the interplay between theory and experiment is in this field.<br/>Here we present a methodology to describe spectral lineshapes from first principles, providing insight into the solvent-solute molecular interactions in terms of static and dynamic disorder and how these shape the signals registered experimentally in 2DES. Water-solvated adenine is chosen as our model to obtain an accurate reference to analyse spectra on larger multimeric species. Our simulations rely on an atomistic description of the water solvent around a frozen adenine moiety obtained with classical molecular dynamics. Two different strategies for simulating lineshapes are tested and confronted: one that employs a single quantum mechanical computation that is perturbed by the water distributions and another where we employ a full hybrid QM/MM treatment over the different water conformations. Both models go beyond standard methods whereby identical contributions to the lineshape are assumed for different electronic transitions and allow extracting the concrete involvement of each partaking electronic excited state. Intra-molecular (relaxation) contributions are also accounted for by including contributions from the normal modes and bright excited state gradients in the simulation. Our simulations provide a realistic description of the lineshapes in 2DES and lead to a concrete molecular counterpart to explain its origin, disentangling broadenings from other contributions to the spectra.

Characterising spectral lineshapes in water-solvated adenine from first-principles

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.