Optical activity of electronically delocalized molecular aggregates: Nonlocal response formulation

Abstract

A unified description of circular dichroism and optical rotation in small optically active molecules, larger conjugated molecules, and molecular aggregates is developed using spatially nonlocal electric and magnetic optical response tensors χ(r,r′,ω). Making use of the time dependent Hartree Fock equations, we express these tensors in terms of delocalized electronic oscillators. We avoid the commonly-used long wavelength (dipole) approximation k⋅r≪1 and include the full multipolar form of the molecule–field interaction. The response of molecular aggregates is expressed in terms of monomer response functions. Intermolecular Coulomb interactions are rigorously taken into account thus eliminating the necessity to resort to the local field approximation or to a perturbative calculation of the aggregate wave functions. Applications to naphthalene dimers and trimers show significant corrections to the standard interacting point dipoles treatment.