Theoretical design of polymeric conductors

We focus on organic polymers that could possess very small bandgaps and therefore display high conductivities intrinsically (i.e., without the need of doping). We concentrate on aromatic polymers such as polythiophene and its derivatives. We establish for those compounds the complete relationship between bandgap and bond-length alternation along the polymer backbone. We discuss certain types of substitution which can provoke an effective quinoid-like contribution to the electronic structure. We describe in particular the electronic properties of polyisothianaphthene as well as polythino[3,4-c]thiophene and polyisonaphtothiophene. We present the conditions under which the latter two compounds might present a vanishingly small bandgap.