Optical properties of V-shaped bis-coumarins: Ab initio insights

Abstract Using a series of ab initio approaches, we investigate the optical spectra of recently synthesised fluorescent bis-coumarins (Tasior et al., 2014). We show that the complex absorption spectra of several derivatives originate in the overlapping of contributions from energetically-close excited-states. These states have been carefully characterised using TD-DFT, ADC(2) and CC2 levels of theory and accounting for solvent effects using the corrected linear response PCM scheme. We show how such a refined protocol is both necessary and useful to investigate photophysics of these bis-coumarins. In addition to an analysis of the nature of the excited-states of these systems, the vibrationally-resolved spectrum was determined for the parent molecule.