Influence of side chain composition and polarity of the environment on the electrochemical doping mechanism in poly[3-(6-hydroxy)hexylthiophene] and dioxythiophene derivatives.
Bargigia I., Savagian L. R., "Osterholm A.M., Nicolini T., Dautel O., Stingelin N., Reynolds J.R., Silva C.
We address the nature of electrochemically induced charged states in conjugated polymers, their evolution as a function of electrochemical potential, and their coupling to their local environment by means of transient absorption and Raman spectroscopies synergistically performed $in situ$ throughout the electrochemical doping process. We use as benchmarks an oligoether-functionalized 3,4-propylenedioxythiophene (ProDOT) copolymer and poly[3-(6-hydroxy)hexylthiophene] (P3HHT). The changes embedded in both linear and transient absorption features show that in the case of P3HHT there is an ultrafast energy transfer between the exciton and the polaron, which is absent in the case of the ProDOT copolymer. In the case of the ProDOT copolymer we also identify a precursor electronic state with charge-transfer character that precedes the polaron formation and bulk electronic conductivity, and it is instead absent in P3HHT. This contribution provides insight into the energetic landscape of a heterogeneous polymer-electrolyte system and demonstrates how such coupling depends on environmental parameters, such as polymer structure, electrolyte composition, and environmental polarity.