To understand the influence of interchromophoric arrangements on photoinduced processes and optical properties of aggregates it is fundamental to assess the contribution of local excitations (charge transfer (CT) and Frenkel (FE)), to exciton states. Here we apply a general procedure to analyze the adiabatic exciton states derived from timedependent density functional theory calculations, in terms of diabatic states chosen to coincide with local excitations within a restricted orbital space. In parallel, motivated by the need of cost-effective approaches to afford the study of larger aggregates, we propose to build a model Hamiltonian based on calculations carried out on dimers composing the aggregate. Both approaches are applied to study excitation energy profiles and CT character modulation induced by interchromophore rearrangements in perylene bisimide aggregates up to a tetramer.The dimer-based approach closely reproduces the results of full-aggregate calculations and an analysis in terms of symmetry-adapted diabatic states discloses the effects of CT/FE interactions on the interchange of the H-/J-character for small longitudinal shifts of the chromophores. 1.Introduction.Improvements in material design and fabrication has determined tremendous advances and applications in the field of organic optoelectronic materials. [1-3] Intermolecular interactions, which strongly depend on the packing arrangement, play a key role in determining the photoinduced processes in aggregates of organic chromophores and the control of chromophore's assembly has become a challenging target in supramolecular chemistry. [4-14] A parallel effort in conceptual comprehension of the underlying fundamental physics of photoinduced processes has led to deep advancements in understanding the influence of interchromophoric arrangements on the optical properties of aggregates, [15][16][17] and in modeling the photoinduced relaxation processes leading to excimer formation. [18][19][20]