Utilizing Vibrational Probes to Monitor Polaron-Anion Interactions during Polymer Electrochemical Doping

Area of Science:

• Materials Science
• Electrochemistry
• Spectroscopy

Background:

• Understanding polaron-ion interactions in conducting polymers is key for applications like bioelectronics and neuromorphic computing.
• Direct experimental methods to probe these interactions are limited, hindering material design.

Purpose of the Study:

• To introduce and validate an in situ spectroelectrochemistry (SEC) approach using the vibrational Stark effect to monitor polaron-ion pairs during electrochemical doping.
• To investigate the evolution of electrostatic interactions and polaron behavior during the doping of mixed ionic-electronic conducting polymers.

Main Methods:

• Developed an in situ SEC technique combining visible, near-infrared, and infrared spectroscopy with the vibrational Stark effect.
• Utilized the ester carbonyl in poly[3-(ethyl-4-butanoate)thiophene-2,5-diyl] (P3EBT) as an internal vibrational probe.
• Employed vibrational solvatochromism and molecular dynamics simulations for probe calibration.

Main Results:

• Identified three distinct stages of electrochemical doping based on spectroscopic changes.
• Observed polaron delocalization at low voltages and localization to single chains at higher voltages due to ion intercalation.
• Quantified significant changes in local electric field strength (up to 5 MV/cm) and correlated them with polaron-ion distance and polymer structure.

Conclusions:

• The vibrational Stark effect probe is a powerful tool for studying electrostatic interactions in mixed conducting polymers.
• Polaron-ion distance, polymer chain coherence, and bipolaron formation are critical factors governing polaron behavior during doping.