Delocalized Polarons in Diketopyrrolopyrrole‐Based Conjugated Polymers: Implications for Near‐Infrared Electrochromism and Beyond

Abstract

Conjugated polymers with delocalized polarons and near‐infrared (IR) absorption properties are promising materials for applications in electrochemical devices. However, the poor stability of low bandgap polymers in electrochemical redox conditions limits the realization of such devices. Herein, a new family of near‐IR absorbing conjugated polymers based on diketopyrrolopyrrole (DPP) derivatives with methoxy substituents to achieve reversible p‐type electrochemical doping with bistable near‐IR electrochromism is designed. The extent of volumetric doping in various electrolytes using cyclic voltammetry and spectroelectrochemistry for optimal electrochemical kinetics and near‐IR contrast is systematically investigated. Further, the spray‐coated films of polymers display high open circuit memory as the methoxylation is increased on the polymer backbone. The contrasting electrochromic memory and kinetics observed for these polymers are mainly ascribed to two factors; i) the effect of backbone structure on the spatial extent of polaron delocalization, and ii) the ionization energy of the polymers. The utility of DPP‐based polymers as energy‐efficient electrochromic optical attenuators (EVOAs) with high near‐IR coloration efficiencies, and an optical attenuation value of 5.1 dB at 1.3 and 1.5 µm wavelengths is demonstrated. Furthermore, the experimental findings are corroborated with theoretical studies to establish that the polaron delocalization length is central to the performance of the device.