The effect of the 3,3' substitution in 9,9,9',9'-tetramethyl-fluorene-dimers with electron donor and withdrawing groups was analyzed. Ground state potential energy surfaces were obtained at DFT level using B3LYP/6-31+G(d,p). All studied dimers are nonplanar at their electronic ground states. The electronic transitions were investigated through the time-dependent-DFT method at their optimized ground states. The chemical potential (mu) as well as the HOMO and LUMO eigenvalues were plotted against the Hammet parameters, showing a good linear correlation, giving us insights about the modulation of the electronic properties, e.g. HOMO-LUMO gap, by means of the functionalization of fluorene dimers at strategical positions. (C) 2012 Elsevier B.V. All rights reserved.