Molecular engineering of the band gap of π-conjugated systems:: Facing technological applications

For almost two decades, the search of an intrinsically-conductive organic metal has represented the major driving force for research on control of the band gap of extended pi-conjugated systems. However, the emergence of the application of pi-conjugated oligomers and polymers in field-effect transistors, light-emitting diodes, electrochromic devices and solar cells has introduced major changes in the chemistry of gap engineering. Besides controlled band gap, active materials for electronic and photonic applications must present appropriate absorption and/or emission properties, highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) energy levels and charge-transport properties. The aim of this short S S review is to present an overview of the recent trends in this area in order to identify possible directions for future research.