Electrochemical Doping Behavior of Oligoether Functionalized Organic Mixed Ionic-Electronic Conductors

Christian Franz^a, Justine Wagner^b, Anna Österholm^b, John Reynolds^b^,^c, Natalie Banerji^a

^aDepartment of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern., Freiestrasse, 3, Bern, Switzerland

^bSchool of Chemistry & Biochemistry, Georgia Institute of Technology, US, Georgia 30332-0400, United States

^cSchool of Material Science and Engineering, Georgia Institute of Technology, US

Proceedings of MATSUS Fall 2024 Conference (MATSUSFall24)

#OMIEC - Understanding Mixed Ionic-Electronic Conductors

Lausanne, Switzerland, 2024 November 12th - 15th

Organizers: Natalie Banerji and Olivier Bardagot

Poster, Christian Franz, 398
Publication date: 28th August 2024

Organic mixed ionic-electronic conductors (OMIECs) are a class of materials that are of great interest in the field of bioelectronics. These materials show a modulation of their electronic conductivity following the oxidation of the OMIEC, which is dependent on the nature of ions that are taken up into the bulk of the material [1]. Optimal OMIEC properties can differ between applications such as biosensors or organic electrochemical transistors (OECTs), which is why we need to study these properties and determine how they can be tuned [2]. Recent highly performing conjugated polymers employ oligoether side chains [3][4], which is the feature that this study aims to shed some light on. To do this, we compared the electrochemical doping of two polymers, one functionalized exclusively with alkoxy side chains and another one with a mixture of alkoxy and oligoether side chains. Both polymers have the same TPT-E (thiophene-phenylene-thiophene-EDOT) backbone, which is planarized through S-O interactions between all neighboring units, yielding films with a well ordered, semicrystalline morphology.

Using spectroelectrochemistry, steady-state Vis-NIR absorbance spectra were obtained at varying applied potentials. Multivariate curve resolution (MCR) was employed to deconvolute the contribution of differently oxidized chromophore species to the absorbance spectra. Additionally, the neutral polymer absorbance was separated into contributions from ordered and disordered film regions, as they show discernable spectral features. The resulting potential-dependent concentrations of these species were used to compare the oxidation behavior of the two polymers. We found that the introduction of oligoether side chains shifts the oxidation of ordered chains by around 0.3 V, whereas the disordered oxidation peak remains largely unaffected. Additionally, we observed that only the oligoether functionalized polymer showed fast kinetics and sufficient stability when used with aqueous electrolytes, highlighting the significant effect of the side chains on the uptake of polar electrolytes.

References:

[1] Flagg, L. Q.; Giridharagopal, R.; Guo, J.; Ginger, D. S. Anion-Dependent Doping and Charge Transport in Organic Electrochemical Transistors. Chem. Mater. 2018, 30, 15, 5380-5389

[2] Paulsen, B. D.; Tybrandt, K.; Stavrinidou, E.; Rivnay, J. Organic mixed ionic-electronic conductors. Nat. Mater. 2020, 19, 13-26

[3] Giovannitti, A.; Sbircea, D.-T.; Inal, S.; Nielsen, C. B.; Bandiello, E.; Hanifi, D. A.; Sessolo, M.; Malliaras, G. G.; McCulloch, I.; Rivnay, J. Controlling the mode of operation of organic transistors through side-chain engineering. Proc Natl Acad Sci U S A, 2016, 113, 43, 12017-12022

[4] Moser, M.; Savagian, L. R.; Savva, A.; Matta, Micaela.; Ponder Jr, J. F.; Hidalgo, T. C.; Ohayon, D.; Hallani, R.; Reisjalali, M.; Troisi, A.; Wadsworth, A.; Reynolds, J. R.; Inal, S.; McCulloch, I. Ethylene Gylcol-Based Side Chain Length Engineering in Polythiophenes and its Impact on Organic Electrochemical Transistor Performance. Chem. Mater. 2020, 32, 15, 6618-6628

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