Absorption and stationary fluorescent spectra of molecular sensors in solution: A computational study

In this study we report the application and the extension of a theoretical-computational method for the modelling of absorption and stationary emission (electronic) spectra of flexible and easily polarizable chromophores embedded in complex environments. The method, similar but computationally less expensive than the most popular Quantum Mechanics/Molecular Mechanics (QM/MM) approaches, is based on a combination of Molecular Dynamics simulations, Quantum-Chemical calculations and elementary statistical mechanics. As a test case we have addressed, in the present study, the spectral features of two solvated chromophores, experimentally shown by our group to be very sensitive to the solvent (environment) polarity, formed by a 4-[4-(1-dimethylamino)phenyl]-pyridine moiety linked to an uracil group through an alkyl spacer of different lengths. The method, despite the involved approximations and intrinsic drawbacks, is able of reproducing both the absorption and emission spectra of the above system as well as the sharp dependency of the spectral observables on the environment polarity. In this respect it might represent an efficient tool, alternative to more accurate QM/MM-based approaches, in cases where their application could be made computationally very expensive.