Electronic absorption spectra of molecules and aggregates with interatomic charge transfer using a normal mode treatment of the atom monopole-dipole interaction model

The theory of the atom monopole-dipole interaction model for electronic polarizability is extended to the case of complex frequency-dependent atom polarizabilities, allowing the prediction of absorption spectra in terms of a set of electronic normal modes. The charge constraints on the system are taken into account using Lagrangian and penalty function methods. Expressions are obtained for the complex polarizability of an aggregate of molecules in which intermolecular charge transfer is precluded. The results are illustrated by calculations for naphthalene using atom polarizability parameters which give an approximate fit to the experimentally observed absorption spectrum. We also treat helical stacked aggregates of naphthalene molecules and predict intensity shifts analogous to those observed in the stacked aromatic bases of helical nucleic acids. (C) 1996 American Institute of Physics.