M. S. THESIS COLLOQUIUM
Name: Mr. Amit Chakraborty
Title: “Modulating Spatial and Temporal Stability of Delocalised Polarons in Diketopyrrolopyrrole-based Electrochromic Polymers”
Date & Time : Friday, 21st March 2025 at 11:00 A.M
Venue: A-104 Lecture Hall, Chemical Sciences Building
Abstract:
Organic Mixed Ionic Electronic Conductors (OMIECs) enable simultaneous electronic and ionic charge transport, making them ideal for electrochemical applications such as Organic Electrochemical Transistors (OECTs), bioelectronics, energy storage systems, and electrochromic devices.[1, 2] Their electrochemical performance is dictated by the degree of polaron delocalization in π-conjugated polymers, particularly in near-infrared (NIR) electrochromism applications. However, achieving stable, long-lived polarons in low-bandgap polymers remains challenging due to parasitic redox reactions compromising their stability.
To address these limitations, we synthesized a series of methoxylated thiophene-diketopyrrolopyrrole (DPP)-based polymers designed to enhance polaron delocalization while improving spatial and temporal stability.[3] By systematically tuning the extent of methoxylation on the polymer backbone, we achieved reversible p-type electrochemical doping with low oxidation onset and bistable NIR electrochromic properties. Our electrochemical and spectroscopic analysis revealed that ion-polymer interactions are crucial in determining the spatial extent of polaron delocalization. The spray-coated thin films also exhibited high open-circuit memory, with ion-dependent differences in doping kinetics and electrochromic response. The contrasting stability and response kinetics were primarily attributed to (i) the effect of backbone structure on ion-mediated polaron delocalization and (ii) the polymer’s ionization energy.
The experimental results, supported by theoretical studies, confirm that controlling polaron delocalization is central to optimizing electrochromic performance. Leveraging these insights, we developed an energy-efficient Electrochromic Variable Optical Attenuator (EVOA), achieving an attenuation value of 5.1 dB at 1.3 and 1.5 µm wavelengths. This study highlights a rational approach to designing polymers with enhanced stability, paving the way for next-generation optical and bioelectronic devices.
References:
- B.D. Paulsen, et. al., Mixed Ionic-Electronic Transport in Polymers, Annu. Rev. Mater. Res, 2021, 51:73–99
- H. Kim, et. al., Organic Mixed Ionic–Electronic Conductors for Bioelectronic Sensors: Materials and Operation Mechanisms, Adv. Science, 2024, 11, 2306191
- D. Giri, et. al., Delocalised Polarons in Diketopyrrolopyrrole-Based Conjugated Polymers: Implications for Near-Infrared Electrochromism and Beyond, Adv. Funct. Mater., 2024, 35, 2410815
