A theoretical study for the dynamic interchromophoric interaction effects upon the susceptibility and hypersusceptibility of chromophore aggregates

The dynamic interchromophoric interaction effects upon the susceptibility and hypersusceptibility of the current–charge density of chromophore aggregates are formulated to infinite order and in closed form by means of a decoupling approximation, whereby the induced field operator contained in the dynamic perturbation Hamiltonian is replaced by its averaged form satisfying the generalized Maxwell’s equation for the current-charge source density. This decoupling approximation includes a basic condition that the total momentum and hence the total current of identical charged particles belonging to any chromophore remain as nearly constant in time throughout the dynamic perturbation interactions. The physical meaning of this condition is surveyed by making reference to the local conservation equation which can be derived for the chromophoric current and charge densities. Contributions of the aggregate’s susceptibility and hypersusceptibility to the mean rate of energy absorption caused by a single-frequency external field and to the mean rate difference generated by right and left circularly polarized light are studied in terms of the frequency reversal symmetries of the susceptibility and hypersusceptibility.