  Ferroelectric $\pi$-stacked molecular wires for solar cell applications are
theoretically designed, in such a way that their energy gaps fall within
visible and infrared range of the Sun radiation. Band engineering is tailored
by a modification of the number of the aromatic rings and via a choice of the
number and kind of the dipole groups. The electronic structures of molecular
wires and the chemical character of the electron-hole pair are analyzed within
the density functional theory (DFT) framework and the hybrid DFT approach by
means of the B3LYP scheme. Moreover, it is found that one of the advantageous
properties of these systems - namely the separate-path electron and hole
transport - reported earlier, still holds for the larger molecules, due to the
dipole selection rules for the electron-hole generation, which do not allow the
lowest optical transitions between the states localized at the same part of the
molecule.
