In this work a quantum chemical investigation is performed on the effects of the interchain distance and orientation on the optical and electronic properties of a few neutral and doubly charged model clusters built from three units of a large-sized oligodiacetylene. The collective electronic oscillator (CEO) approach, based on the INDO/S Hamiltonian, was used for the calculation of the transition energies as well as of the one-electron transition density matrices of these large supra-molecular systems, due to its intrinsic computational advantages. Among the main results, it is shown that the number of forbidden excited states generated by the aggregations effects and the distribution of the excess charge in the clusters are strongly affected by the interchain distance and relative orientation of the cluster units. The analysis of the plots of the one-electron transition density matrices and of the intra- and interchain probabilities of electron-hole pair generation allows to describe the nature of the excitations, their delocalization and their charge-transfer character, and to identify the cluster units involved in the photon absorption process. These results give information for designing supra-molecular architectures with desired photophysical properties.