Electron density analysis of aromatic complexes in excited electronic states: The benzene and naphthalene excimers

This paper presents an energetic and electron density analysis of intermolecular complexes in excited states. The electron distributions of the benzene and the naphthalene dimers, ( C 6 H 6 ) 2 and ( C 10 H 8 ) 2 , are studied at selected intermolecular configurations in the ground and first singlet excited states. The electrostatic contribution to the interaction energy of the benzene and the naphthalene excimers is analyzed in terms of changes on the electron density accompanying the transitions related to their electronic spectra. Some descriptors from the quantum theory of atoms in molecules and the NCI index are analyzed for these complexes in both states. These properties reveal that whereas the first order density does not explain the larger stability of the excimers compared to the ground state complexes, the intermolecular electron delocalization, a second order property, shows definite trends. The increase of intermolecular electron sharing can thus be considered a measure of the delocalization of the excitation energy in the electronic transitions.