AbstractPolyaniline (PANI) has attracted lasting interest due to its unconventional electronic, optical, and electro‐optical properties. A rigid backbone polymer, PANI exhibits very strong intra‐ and intermolecular interactions governing its overall behavior. The purpose of this study is to investigate theoretically the contribution of the various inter‐ and intramolecular interactions to the process of organization of PANI macromolecules in aqueous environment. The structure and spectral conduct of oligoanilines (tetramers) in different oxidation states have been calculated at the Monte Carlo/Molecular Mechanics (MC/MM) and quantum chemical (QC) semiempirical level. The effect of protonation on the optical properties of partially and fully oxidized oligomers is discussed. The role of intermolecular interactions and the influence of water as a solvent are estimated for a number of hydrated clusters. Computed results and experimental spectra are compared. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006