Ion Size-Dependent Electrochromism in Air-Stable Napthalenediimide-Based Conjugated Polymers

Giri, D and Saha, SK and Siemons, N and Anderson, I and Yu, H and Nelson, J and Canjeevaram Balasubramanyam, RK and Patil, S (2022) Ion Size-Dependent Electrochromism in Air-Stable Napthalenediimide-Based Conjugated Polymers. In: ACS Applied Materials and Interfaces, 15 (14). pp. 17767-17778.

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Abstract

Conjugated polymers (CPs) that show stable and reversible cation insertion/deinsertion under ambient conditions hold great potential for optoelectronic and energy storage devices. However, n-doped CPs are prone to parasitic reactions upon exposure to moisture or oxygen. This study reports a new family of napthalenediimide (NDI) based conjugated polymers capable of undergoing electrochemical n-type doping in ambient air. By functionalizing the NDI-NDI repeating unit with alternating triethylene glycol and octadecyl side chains, the polymer backbone shows stable electrochemical doping at ambient conditions. We systematically investigate the extent of volumetric doping involving monovalent cations of varying size (Li+, Na+, tetraethylammonium (TEA+)) with electrochemical methods, including cyclic voltammetry, differential pulse voltammetry, spectroelectrochemistry, and electrochemical impedance spectroscopy. We observed that introducing hydrophilic side chains on the polymer backbone improves the local dielectric environment of the backbones and lowers the energetic barrier for ion insertion. Surprisingly, when using Na+ electrolyte, the polymer films exhibit higher volumetric doping efficiency, faster-switching kinetics, higher optical contrast, and selective multielectrochromism when compared to Li+ or TEA+ electrolytes. Using well-tempered metadynamics, we characterize the free energetics of side chain-ion interactions to find that Li+ binds more tightly to the glycolated NDI moieties than Na+, hindering Li+ ion transport, switching kinetics, and limiting the films’ doping efficiency.

Item Type:	Journal Article
Publication:	ACS Applied Materials and Interfaces
Publisher:	American Chemical Society
Additional Information:	The copyright for this article belongs to American Chemical Society.
Keywords:	Cyclic voltammetry; Electrochemical impedance spectroscopy; Electrochromism; Electrolytes; Polymer films; Positive ions; Semiconducting films; Semiconductor doping; Spectroelectrochemistry, Ambient conditions; Based conjugated polymers; Cation transports; Glycol side chain; Ion selectivity; Li +; Polymer backbones; Side-chains; Volumetric doping; Volumetrics, Conjugated polymers
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	29 May 2023 03:19
Last Modified:	29 May 2023 03:19
URI:	https://eprints.iisc.ac.in/id/eprint/81536

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