Cyclopentadithiophene (CPDT) Dimer Dication:  Bipolaron Model for Quaterthiophenes

Cyclopentadithiophene (CPDT) dimers in which both 3,3‘ and 4‘ ‘,3‘ ‘‘ positions were bridged with 1,3-dioxalane, carbonyl, or dicyanovinylidene were prepared. These compounds have small HOMO−LUMO gaps (1.03−2.25 eV). The electrochemical oxidation of a dicyanovinylidene-bridged CPDT dimer gave a dication that had a quinoid-like structure.