In this paper, we present the results of a theoretical study of the electronic and optical excitations of isolated carbazolyl-substituted oligodiacetylenes using the collective electronic oscillator (CEO) method. Within this technique the excitations are directly connected to the corresponding one-electron transition density matrices, obtained as eigenmodes of the time dependent Hartree-Fock (TDHF) Liouville operator, which represent motions of electron/hole pairs. The two-dimensional plot of the transition density matrix (CEO mode) establishes the physical connection between the electronic spectra and the electronic rearrangement due to the photon absorption. Consequently this representation allows for an intuitive interpretation of the optical spectra in terms of the chemical structure, and gives a useful tool for the design of molecules showing the required physical properties. (C) 2003 Elsevier B.V. All rights reserved.