The effects of band shapes on circular dichroism spectra of chromophore aggregates

The problem of calculating circular dichroism (CD) spectra for aggregates of chromophores with nonoverlapping wavefunctions is formulated in a general way with regard to band shapes. An immediate consequence of this formulation is that a series of exact and approximate results derived previously for aggregate absorption spectra apply to CD as well. It is shown that the contribution to aggregate CD from magnetic transition dipoles of the individual chromophores can always be written as a function of the intrinsic CD of the noninteracting chromophores. It is further shown, making use of a specific example, that there are whole classes of aggregate CD spectra which arise solely as a consequence of finite bandwidths. These spectra are qualitatively different from what is expected in the exciton limit, i.e., the limit of vanishing bandwidth.