Comparative study of the oxidation of fluorene and 9,9-disubstituted fluorenes and their related 2,7′-dimers and trimer

Electroactive polyfluorene films were obtained by anodic coupling of fluorene and a series of 9,9-disubstituted fluorenes and their related 2,7'-dimers and trimer. The polymerization mechanism is discussed in light of cyclic voltammetry investigations in organic media using the classical millimetric electrode and ultramicroelectrodes, DFT theoretical calculations, and laser flash photolysis experiments. The first step of electropolymerization involves the formation of the carbon-carbon bond through the coupling between two fluorene radical cations. However, the radical cation of the produced dimer is not reactive enough to repeat the coupling reaction as in the classical electropolymerization mechanism. To continue the polymerization, formation of a higher oxidation state is required. This behavior is supported by theoretical expectations.