Geometric and electronic structure of polydicyanomethylene-cyclopenta-dicyclopentadiene, a conjugated polymer possessing a very small intrinsic bandgap

We present a detailed theoretical analysis of the geometric and electronic structure of polydicyanomethylene-cyclopentadicyclopentadiene, a polymer made by the succession of bicyclopentadiene units in which the two rings are linked by a dicyanomethylene moiety. It is shown that the small calculated bandgap, 0.16 eV, is mainly due to a strong stabilizing interaction occurring between the LUMO of the conjugated skeleton associated to the polymer and the LUMO of the electron-withdrawing group.