Molecular engineering of organic polymers with a very small intrinsic bandgap : a theoretical approach

We present results of theoretical calculations aiming at designing new organic polymers which would be intrinsically good electrical conductors. For aromatic polymers such as polythiophene, we establish a linear relationship between the bandgap value and the importance of quinoid contributions to the geometry. In the framework of this relationship, we describe the electronic properties of polyisothianaphthene as well as polythieno[3,4-c]thiophene and polyisonaphtothiophene. We discuss the conditions which could lead to a very small bandgap in the latter two compounds