The molecular design of conjugated polymers for efficient organic photovoltaic devices (OPVs) providing advantageous processing properties, namely solubility in low toxic solvents as ethanol, is an important issue for the
progress of OPV technology. In this work, the pattern substitution and chemical nature of the side chain, either nalkoxy or oligo(ethylene oxide) groups, in alternating thiophene-quinoxaline copolymers is varied and their
effect in polymer chain grow, solubility and optical spectra is thoroughly analyzed in light of quantum mechanical calculations. Although the polymer with oligo(ethylene oxide) groups exhibited good solubility in
ethanol, it was found that substituting in both meta- and para-positions of the peripheral phenyl rings attached to
the quinoxaline groups causes smaller molecular weight, lower solubility in chlorinated solvents and poorer
performance in photovoltaic devices. The theoretical studies revealed differences in the most energetically
favored conformers for each case of the polymers’substitution pattern that can justify the observed results.