An efficient theoretical framework for studying multi-chromophore systems like PAH aggregates is the Frenkel exciton model, in which the excited states of the system are described as a linear combination of local excitation (LE) diabatic states on each chromophore, and the coupling between the LE states are approximated by the Columbic interaction between their transition dipoles. Subsequently, Yamagata and Hestand introduced charge transfer (CT) diabatic states into the exciton model enabling it to describe systems with nonnegligible LE-CT coupling such as PAH aggregates and organic crystals. Based on the extended exciton model, efficient quantum chemical methods have been developed that can correctly describe the properties of multiple chromophore systems and analyze the coupling between LE and CT states. These previous works have established a solid theoretical basis for the study of the structure-fluorescence relationship of asphaltene aggregates.