The Absorption Band Shapes of a Push-Pull Dye Approaching the Cyanine Limit: A Challenging Case for First Principle Calculations of Ground and Excited State Molecular Properties in Solution

The absorption band shapes of a donor-acceptor dye whose electronic structure can be finely tuned from push-pull to cyanine limit upon changing solvent polarity, have been theoretically investigated by using Kubo’s generating function approach, with minimum energy geometries and normal modes computed at DFT level of theory. The comparison of the observed and predicted absorption band shapes and the analysis of dipole moment variations upon excitation reveal that a delicate balance of HartreeFock exchange in the functional is needed to treat such a difficult systems by density