Excited states behavior of nucleobases in solution: insights from computational studies

We review the most significant results obtained in the study of isolated nucleobases in solution by quantum mechanical methods, trying to highlight also the most relevant open issues. We concisely discuss some methodological issues relevant to the study of molecular electronic excited molecular states in condensed phases, focussing on the methods most commonly applied to the study of nucleobases, i.e. continuum models as the Polarizable Continuum Model and explicit solvation models. We analyse how the solvent changes the relative energy of the lowest energy excited states in the Franck-Condon region, their minima and the Conical Intersections among the different states, interpreting the experimental optical spectra, both steady state and time-resolved. Several methods are available for accurately including solvent effects in the Franck-Condon region, and for most of the nucleobases the solvent shift on the different excited states can be considered assessed. The study of the excited state decay, both radiative and non-radiative, in solution still poses instead significant theoretical challenges

Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening

Photoinduced isomerization reactions lie at the heart of many chemical processes in nature. The mechanisms of such reactions are determined by a delicate interplay of coupled electronic and nuclear dynamics occurring on the femtosecond scale, followed by the slower redistribution of energy into different vibrational degrees of freedom. Here we apply time-resolved photoelectron spectroscopy with a seeded extreme ultraviolet free-electron laser to trace the ultrafast ring opening of gas-phase thiophenone molecules following ultraviolet photoexcitation. When combined with ab initio electronic structure and molecular dynamics calculations of the excited- and ground-state molecules, the results provide insights into both the electronic and nuclear dynamics of this fundamental class of reactions. The initial ring opening and non-adiabatic coupling to the electronic ground state are shown to be driven by ballistic S–C bond extension and to be complete within 350 fs. Theory and experiment also enable visualization of the rich ground-state dynamics that involve the formation of, and interconversion between, ring-opened isomers and the cyclic structure, as well as fragmentation over much longer timescales

Photoinduced processes in nucleic acids

Photoinduced processes in nucleic acids are phenomena of fundamental interest in diverse fields, from prebiotic studies, through medical research on carcinogenesis, to the development of bioorganic photodevices. In this contribution we survey many aspects of the research across the boundaries. Starting from a historical background, where the main milestones are identified, we review the main findings of the physical-​chemical research of photoinduced processes on several types of nucleic-​acid fragments, from monomers to duplexes. We also discuss a number of different issues which are still under debate