Quartz crystal impedance and EQCM measurements applied to dithienothiophene-based polymers

Dithienothiophene polymers are promising materials for advanced electrochemical devices and the copolymerization from different dithienothiophene isomers represents a useful tool to tune the electronic and electrochemical properties of these conducting polymers. The present paper reports and discusses polymer quartz crystal (QC) impedance measurements carried out with a frequency response analyzer in the QC resonance frequency region as well as electrochemical quartz crystal microbalance (EQCM) data during the p-doping and undoping processes of poly(dithieno[3,4-b:3',4'-d]thiophene) (pDTT1), poly(dithieno[3,4-b:2',3'-d]thiophene) (pDTT3) and poly(dithieno[3,4-b:3',4'-d]thiophene-co-dithieno[3,4-b:2',3'-d]thiophene) 50/50 (p(DTT1-co-DTT3) 50/50). The QC impedance measurements were performed to determine whether the mechanical properties of these polymers change with thickness and in different states of charge, thereby to ensure a correct application of the EQCM technique to the dithienothiophene-based polymers. The EQCM measurements were carried out to investigate whether the different geometries of DTT1 and DTT3, which can lead to different enchainments in the resulting polymers, affect the mass transport phenomena during the p-doping and undoping processes of pDTT1, pDTT3 and p(DTT1-co-DTT3) 50/50.