Application of density functional theory in the synthesis of electroactive polymers

A wide range of conjugated organic compounds undergo anodic electropolymerisation to produce polymers of high conductivity. However, electrooxidation does not always result in the formation of electroactive materials, since some reactions produce insulating films or soluble oligomers. Density functional theory (DFT) has been used to predict the outcome of electropolymerisation reactions by calculating the unpaired electron x-spin density distribution of monomeric radical cations, in order to determine coupling positions in the resultant polymers. x-Spin densities calculated for pyrrole, thiophene and (€)-stilbene are found to be in good agreement with experimental values. DFT has been used to investigate the low conductivity and redox inactivity of poly[(E)-3- styrylthiophenes] and poly[(E)-2-styrylheterocycles]. High positive spin densities at the alkene spacer linkage in the corresponding monomeric radical cations were found, suggesting crosslinking of the polymers via the double bond. In contrast, electroactive polymers of improved conductivity are formed from the electropolymerisation of some (Z)-2-a,b-diarylacrylonitriles. For these monomers, DFT calculations show the positions of highest spin density to be located at the a-positions of the heterocyclic rings, suggesting the presence of a,a'-linked monomeric couplings necessary for electroactivity.