Identification of the Interchromophore Interaction on Electronic Absorption and Circular Dichroism Spectra of Bis-Phenanthrenes

We characterize the low-lying excited electronic states of a series of bis-phenanthrenes by our newly developed diabatic scheme called the fragment particle-hole densities (FPHD) method and calculate both the electronic absorption and circular dichroism (ECD) spectra by the time-dependent density functional theory (TDDFT) and the FPHD-based exciton model which couples intrachromophore local excitations (LEs) and the interchromophore charge-transfer excitations (CTEs). TDDFT treats each bis-phenanthrene as a single molecule while the mixed LE-CTE exciton model partitions the molecule into two phenanthrene-based aromatic moieties, then applies the electronic couplings among the various quasi-diabatic states to cover the interactions. It is found that TDDFT and the mixed LECTE model reproduce all experimentally observed trends in the spectral profiles, and the hybridization between LE and CTE states displays differently in absorption and ECD spectral intensities, as it usually decreases the absorption maxima and affects the ECDs’ positive/negative extrema irregularly. By comparing the results yielded by the LE-CTE model with and without the LE-CTE couplings, we identify the contribution of CTE on the main dipole-allowed transitions.