Polythiophene-cellulose composites: synthesis, optical properties and homogeneous oxidative co-polymerization

Composites of cellulose and conjugated polymers based on oligo- and polythiophene are reported, inspired by the assembly of cellulose and lignin in wood as a composite that survives harsh environmental conditions and meets most complex demands. The regioselectively oligothiophene-substituted cellulose derivatives were synthesized according to a protecting group strategy and used to prepare the polythiophene-cellulose composites through a FeCl3-initiated oxidative co-polymerization with thiophene co-monomers. The optical property of the cellulose derivatives with mono-, bi- and terthiophene moieties at the C-6 position was investigated with ultraviolet-visible (UV-Vis) and circular dichroism (CD) spectroscopy. The UV-Vis absorption spectra exhibited a broad band reflecting the intense pi-pi* transition within the conjugated oligothiophene side chains, which were greater than those of the corresponding reference monomers owing to their intermolecular pi-electron interactions, even in solution. This was also supported by the negative CD band, indicative of cellulosic supramolecular stacking structures in solution. The soluble polythiophene-cellulose composites were prepared by the oxidative co-polymerization of the oligothiophene substituted celluloses with excess 3-hexylthiophene in the presence of FeCl3 as the oxidative initiator. The supplied amount of thiophene co-monomer was crucial for producing large pi-conjugated structures and a cross-linked network structure. The soluble composites, with properties, such as electric conductivity, semiconductivity, or photoelectroactivity, were applied for the preparation of thin films which will have to be optimized for the respective application.