The formation of stable pi-stacked dimers constituted by thiophene-containing molecules in the radical cation state has been investigated using different theoretical methods. Calculations on systems formed by two thiophenes and two 2,2'-bithiophenes, where the two molecules of each dimer are oxidized, provided one and two pi-stacked complexes, respectively. The molecular geometry and electronic properties of the molecules within each complex have been analyzed and compared with those calculated for the isolated molecule. Furthermore, the effect of dimerization on lowest pi-pi* transition energy has been examined and related with the inter-molecular delocalization of pi-electrons in thiophene-containing doped systems. (C) 2010 Elsevier B.V. All rights reserved.