Parole chiave: Optical Spectra Solution Vibrational Calculations Td-Dft,
*** IBB - CNR *** n class="highlight" style="background-color:">Institute of Biostructure and Bioimaging - CNR, Naples, Italy.
We here report a thorough quantum mechanical study of the optical properties of several <em class="EmphasisTypeItalic ">N</em>-succinimidyl-ester<br> and methyl-amide derivatives of bi- and terthiophene, which have shown <br>promising performances as biomarkers. We study in particular the <br>dependence of the absorption and emission spectra on the substituents <br>and on the nature of the embedding medium, from the gas phase to polar <br>solvents. Our approach is based on time-dependent density functional <br>theory calculations, by comparing the performances of different <br>functionals and, finally, using long-range-corrected CAM-B3LYP as <br>reference functional. Solvent effects are included by the Polarizable <br>Continuum Model, exploiting both its linear response and state-specific <br>implementations. In order to simulate the absorption spectra at room <br>temperature, a hybrid quantum/classical approach is adopted where the <br>broadening effects due to the torsional flexibility of the system are <br>taken into account within the classical Franck–Condon principle, <br>starting from a relaxed three-dimensional potential energy surface, <br>while the quantum vibronic contribution of the remaining degrees of <br>freedom is described in harmonic approximation according to a <br>time-dependent approach. The theoretical predictions are in good <br>agreement with experiments, providing interesting indications on the <br>accuracy of different functionals and on the main chemical-physical <br>effects modulating the excited state properties of these compounds.