Quantifying internal charge transfer and mixed ion-electron transfer in conjugated radical polymers

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Macromolecular radicals are key functional materials for energy storage and electronics.
• Conjugated radical polymers often exhibit lower conductivity than their non-conjugated counterparts.
• Internal charge transfer between redox-active radical units and conjugated backbones is hypothesized to cause this performance gap.

Purpose of the Study:

• To quantify the internal charge transfer process in conjugated radical polymers.
• To investigate the role of nitroxide radicals in polythiophene conductivity.
• To explore potential applications of these materials beyond energy storage.

Main Methods:

• Synthesis of polythiophene loaded with varying percentages (0, 25, 100%) of nitroxide radicals (2,2,6,6-tetramethyl-1-piperidinyloxy [TEMPO]).
• Electrochemical analysis using cyclic voltammetry.
• Deconvolution of cyclic voltammograms to separate faradaic and non-faradaic contributions.

Main Results:

• Internal charge transfer was successfully quantified in TEMPO-loaded polythiophene.
• Cyclic voltammograms revealed mixed faradaic and non-faradaic processes contributing to charge transfer.
• Mixed ion-electron transfer was observed in the 100% TEMPO-loaded polymer, involving triflate anions and propylene carbonate molecules.

Conclusions:

• Internal charge transfer significantly hinders conductivity and capacity in conjugated radical polymers.
• The findings explain the performance limitations of these materials.
• These macromolecular radicals may find future applications as voltage regulators.