Electronic Circular Dichroism in Exciton-Coupled Dimers: Vibronic Spectra from a General All-Coordinates Quantum-Dynamical Approach

We present a computational approach of general applicability to simulate the vibronic line shapes of absorption and electronic circular dichroism (ECD) spectra in rigid exciton-coupled dimers based on a time-dependent expression of the spectra and quantum dynamical calculations. We adopt a diabatic model of interacting states localized on the monomers whose electronic potential energy surfaces are described within harmonic approximation, including the effect of displacements, frequency changes, and normal-mode mixings. Spectra that fully account for the effect of all nuclear degrees of freedom of the system are obtained through a hierarchical representation of the Hamiltonian in blocks, defined so that few blocks accurately describe the short-time dynamics of the system. With this approach, on the ground of time-dependent density functional theory calculations, we simulate the absorption and ECD spectra of a covalent compound representing a “dimer” of anthracene, in the spectral region of the 1La monomer transition, obtaining results in good agreement with the experiment.