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Charge-Transfer Intermediates in the Electrochemical Doping Mechanism of Conjugated Polymers

preprint
submitted on 07.10.2020 and posted on 08.10.2020 by Ilaria Bargigia, Lisa R. Savagian, Anna M. Österholm, John R. Reynolds, Carlos Silva
In this work, 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. In particular, we investigate the fundamental mechanism of electrochemical doping in an oligoether-functionalized 3,4-propylenedioxythiophene (ProDOT) copolymer. The changes embedded in both linear and transient absorption features allow us to identify a precursor electronic state with charge-transfer (CT) character that precedes polaron formation and bulk electronic conductivity. This state is shown to contribute to the ultrafast quenching of both neutral molecular excitations and polarons. Raman spectra relate the electronic transition of this precursor state predominantly to the Cβ -Cβ stretching mode of the thiophene heterocycle. We characterize the coupling of the CT-like state with primary excitons and electrochemically induced charge separated states, providing insight into the energetic landscape of a heterogeneous polymer-electrolyte system and demonstrate how such coupling depends on environmental parameters, such as polymer structure, electrolyte composition, and environmental polarity.

Funding

DMREF: Metallic-type transport in polymers: Establishing materials design criteria and predicting structure/property interrelations

Directorate for Mathematical & Physical Sciences

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Air Force Office of Scientific Research (grant number FA9550-18-1-0184)

Office of Naval Research (grant number N00014-20-1-2129)

National Science Foundation Graduate Research Fellowship under Grant No. DGE-1650044

History

Email Address of Submitting Author

carlos.silva@gatech.edu

Institution

Georgia Institute of Technology

Country

United States

ORCID For Submitting Author

0000-0002-3969-5271

Declaration of Conflict of Interest

The authors declare no conflict of interest

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