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1. In operando optical characterization of organic mixed ionic–electronic conductors for unraveling charge transport and doping dynamics—A perspective

   https://doi.org/10.1063/5.0274369  

   Chen, Linqi; Ma, Yingying; Guo, Peijun (July 2025, The Journal of Chemical Physics)

   Organic mixed ionic–electronic conductors (OMIECs) are a unique class of soft, conjugated polymeric materials. The simultaneous electronic and ionic transport of OMIECs enables a new type of device, namely, organic electrochemical transistors, among other emerging technologies. However, the dynamic nature—where charge transport, doping kinetics, and morphological changes occur concurrently—poses significant challenges in the characterization and understanding of OMIECs. Recent advances in in situ optical techniques, including ultraviolet–visible–near-infrared spectroscopy, Raman spectroscopy, and microscopy imaging, have provided valuable insights into the charge transport mechanisms and ionic doping dynamics spanning from the microscopic to the device scale. In this perspective, based on several archetypal OMIECs, we survey how spectroscopic signatures were used to reveal key physical processes in these materials. Looking forward, we propose that ultrafast spectroscopy and microscopy techniques—such as transient absorption spectroscopy, terahertz time-domain spectroscopy, pump–probe microscopy, and photothermal microscopy—hold great potential for uncovering more fundamental mechanisms of OMIEC operation, including quasiparticle dynamics, intrinsic electrical conductivity, and carrier mobility, which remain under-explored. Integrating optical characterization with electrochemical measurements will enable in operando studies on state-of-the-art devices, with results further refined by parallel advancements in theoretical modeling. Altogether, we envision in operando optical characterization with spatial, spectral, and temporal resolution across multiple scales as a powerful pathway to advance the understanding of OMIEC mechanisms and their structure–property relationships. 

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2. Advances and opportunities in development of deformable organic electrochemical transistors

   https://doi.org/10.1039/D0TC03118F  

   Khau, Brian V.; Scholz, Audrey D.; Reichmanis, Elsa (November 2020, Journal of Materials Chemistry C)

   null (Ed.)

   Organic electrochemical transistors (OECTs) have been revived as potentially versatile platforms for bioelectronic applications due to their high transconductance, direct ionic-electronic coupling, and unique form factors. This perceived applicability to bioelectronics can be attributed to the incorporation of organic mixed conductors that facilitate both ionic and electronic transport, enabling material-inherent translation from biological signals to abiotic readouts. In the past decade, multiple synthetic breakthroughs have yielded channel materials that exhibit significant hole/electron transport while displaying electroactivity in aqueous media. Yet, implicit in the rationale of OECTs as bioelectronic devices is they can be fabricated to be mechanically compatible with biological systems, even though unified guidelines for deformable OECTs remain unclear. In this Perspective, we highlight recent advances for imparting deformability. Specifically, materials selection, design, and chemistry for integral parts of the transistor – substrate, electrolyte, interconnects, and (polymeric) channel materials—will be discussed in the context of benchmarks set by select bioelectronics applications. We conclude by identifying key areas for future research towards mechanically compliant OECTs. 

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3. Ion transport in polymeric ionic liquids: recent developments and open questions

   https://doi.org/10.1039/c8me00114f  

   Ganesan, Venkat (April 2019, Molecular Systems Design & Engineering)

   Polymeric ionic liquids (PILs) are an emerging class of materials that combine the attractive properties of ionic liquids with the sequence complexity and mechanical characteristics of macromolecules. While significant advances have occurred in the context of synthesis and characterization of such materials, comparatively less understanding exists on the mechanisms underlying ion transport in such materials. In this perspective article, the status of understanding in related systems of salt-doped polymer electrolytes, (non-ionic-liquid-based) single-ion polymer conductors and room temperature ionic liquids is briefly reviewed. Subsequently, some recent developments in the context of PILs are discussed to identify some open questions confronting the issue of ion transport in such materials. 

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4. Mechanics and Dynamics of Organic Mixed Ionic-Electronic Conductors

   https://doi.org/10.1115/1.4068298  

   Wang, Xiaokang; Yang, Xixian; Mei, Jianguo; Zhao, Kejie (May 2025, Applied Mechanics Reviews)

   Abstract Organic mixed ionic-electronic conductors (OMIECs) are a class of materials that can transport ionic and electronic charge carriers simultaneously. They have shown broad applications in soft robotics, electrochemical transistors, and bio-electronics. The structural response of OMIECs to the mixed conduction populates from molecular conformation to devices, presenting challenges in understanding their mechanical behavior and constitutive descriptions. Furthermore, OMIECs feature strong multiphysics interactions among mechanics, electrostatics, charge conduction, mass transport, and microstructural evolution. In this review, we summarize recent progress in mechanistic understanding of OMIECs and highlight dynamics and heterogeneity underlying each element of mechanics. We introduce strain activation and breathing, mechanical properties, and degradation of OMIECs upon electrochemical doping and dedoping. Drawing on the state-of-the-art experimental and simulation insights, we highlight the critical role of multiscale dynamics in governing the functionality of OMIECs. We discuss the current understanding and limitation of constitutive relations and present computational frameworks that integrate multiphysics. We synthesize mechanics-driven strategies—spanning strain modulation, material stretchability, and interfacial stability—from molecular design to macroscopic structural engineering. We conclude with our perspective on the outstanding questions and key challenges for continued research. This review aims to organize the fundamental mechanical principles of OMIECs, offering a multidisciplinary framework for researchers to identify, analyze, and address mechanical challenges in mixed conducting polymers and their applications. 

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5. The influence of counterion structure identity on conductivity, dynamical correlations, and ion transport mechanisms in polymerized ionic liquids

   https://doi.org/10.1063/5.0159298  

   Zhang, Zidan; Krishna, Ram; Zofchak, Everett S.; Marioni, Nico; Sachar, Harnoor S.; Ganesan, Venkat (August 2023, The Journal of Chemical Physics)

   We used equilibrium and non-equilibrium atomistic simulations to probe the influence of anion chemistry on the true conductivity, dynamical correlations, and ion transport mechanisms in polymeric ionic liquids. An inverse correlation was found between anion self-diffusivities, ionic mobilities, and the anion size for spherical anions. While some larger asymmetric anions had higher diffusivities than smaller spherical anions, their diffusivities and mobilities did not exhibit a direct correlation to the anion volumes. The conductivity and anion dynamical correlations also followed the same trends as displayed by the diffusivity and mobility of anions. All the systems we examined displayed positively correlated motion among anions, suggesting a contribution that enhances the conductivity beyond the ideal Nernst–Einstein value. Analysis of ion transport mechanisms demonstrated very similar hopping characteristics among the spherical anions despite differences in their sizes. 

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