Effect of Microhydration in Tuning the Photophysical Behavior of a Luminescent DNA Probe Revealed by Non-Adiabatic Dynamics

We report non-adiabatic dynamics, performed in the surface hopping formalism, of 2-thienyl-3-hydroxychromone, an environment-dependent luminescent organic DNA probe. In particular we have shown that the first shell solvent water molecules undergo a rather complex reorganization upon light excitation. This involves also the triggering of a water-mediated proton transfer process which leads to the formation of the tautomeric structure. The presence of this solvent-mediated transfer mechanism globally diminishes the intersystem crossing efficiency, and hence the population of the triplet state manifold, as compared to the non-solvated systems. Our results also point out the non-innocent role of solvent networks in tuning complex photophysical processes, while opening competitive relaxation channels.