Renee Kroon

The transition to sustainable electronics requires electroactive materials that are processable in green solvents, operationally stable, and recyclable or recoverable at their end of life. This work explores recoverable electroactive cellulose coatings using a carboxylate-functionalized polar polythiophene (PCAT-K). PCAT-K is water-processable and can be reversibly fixated onto cellulose threads by modulation of the secondary interactions via acid–base chemistry, showing promise for circular material use. To obtain electrically conducting PCAT-K-cellulose threads, acid-mediated oxygen doping of the PCAT-K with p-toluenesulfonic acid was explored but led to undesired covalent cross-linking and loss of solubility and recoverability. Through spectroscopic and electrochemical analyses, it is shown that the covalent cross-linking originates from hydrogen peroxide generation during the doping process, which further reacts with PCAT to form hydroxyl radicals. To suppress radical formation, potassium iodide is introduced as a benign additive that catalytically decomposes hydrogen peroxide, preventing covalent cross-linking while maintaining electrical conductivity and recoverability. While the additive can negatively affect cellulose substrates at long doping times, this strategy allows for stable, conductive, and removable electroactive coatings on cellulose threads using water as the sole solvent. This study highlights a more reliable synthetic route to the water-processable conjugated polymer PCAT-K and suggests a mechanistic origin of acid-mediated oxygen doping-induced covalent cross-linking with a practical strategy to overcome it.

We report a stable diazadioxa[8]circulene radical cation R1, which can be obtained either through chemical oxidation or by electrochemical methods. The stable radical cation R1 shows distinct photophysical and aromatic properties compared to C1.

Organic electrochemical transistors (OECTs) are key bioelectronic devices with applications in neuromorphics, sensing, and flexible electronics. OECTs made using biobased and biodegradable materials are emerging as a sustainable alternative to nondegradable plastic and metal-based electronics. Printing is the key technique used to fabricate these types of devices, enabling fabrication at room temperature and using benign solvents, such as water. However, printing techniques suffer from relatively low resolution (tens to hundreds of micrometers), far below the micrometer resolution achieved via conventional metal deposition and photolithography. Here, we present a high-throughput additive-subtractive microfabrication strategy for carbon-based flexible OECTs using biodegradable materials and room-temperature processing. Additive manufacturing of large features is achieved via extrusion printing of a graphene ink to fabricate electrode contacts on cellulose acetate (CA), which serves both as the substrate and as the insulation layer. Combined with femtosecond (fs) laser ablation, this approach enables micrometer-resolution patterning of freestanding OECTs with channel openings down to 1 μm and sheet resistance below 10 Ω/sq. By tuning laser parameters, we demonstrate both selective and simultaneous ablation strategies, enabling the fabrication of horizontal, vertical, and planar-gated OECTs, as well as complementary NOT gate inverters. Thermal degradation studies in air show that over 80% of the device mass decomposes below 360 °C, providing a low-energy route for device disposal and addressing the environmental impact of electronic waste. This approach offers a lithography-free pathway toward the rapid prototyping of high-resolution, sustainable organic electronics, combining circularity, process simplicity, and architectural versatility for next-generation bioelectronic applications.

Polymer‐based organic mixed ion‐electron conductors (OMIECs) are a class of materials offering unique coupled dual charge transport characteristics along with appealing properties including mechanical softness, biocompatibility, tunability, volumetric capacitance, and stability. These features have been exploited in devices including organic electrochemical transistors (OECTs), neuromorphic computing, energy storage, sensors, neural electrodes, and actuators. Conventionally, OMIEC polymers are prepared through chemical, vapor‐phase, electrochemical, or enzymatic polymerization, typically relying on oxidants, metal catalysts, and/or organic solvents, significantly limiting their scalability, sustainability, and biocompatibility. Here, we introduce an initiator‐free, visible‐light‐induced polymerization of water‐soluble conducting polymer precursors, enabling facile formation of high‐performance and inherently biocompatible OMIECs. This novel approach allows direct photopatterning and seamless film deposition and manufacturing of OECTs across rigid, flexible, and biological substrates, exemplified by glass, textiles, and mouse skin (in vivo). Through careful optimization of the photopolymerization process, resulting OMIECs possess state‐of‐the‐art electrical, electrochemical, and device properties along with exceptional compatibility and conformability with various flexible and biological surfaces. Finally, we demonstrate the utility of these photopatterned electrodes, manufactured directly on mouse skin in vivo, where they significantly enhance the recording efficacy and signal‐to‐noise ratio of low‐frequency brain activity in anesthetized mice.

Polymer‐based organic mixed ion‐electron conductors (OMIECs) are a class of materials offering unique coupled dual charge transport characteristics along with appealing properties including mechanical softness, biocompatibility, tunability, volumetric capacitance, and stability. These features have been exploited in devices including organic electrochemical transistors (OECTs), neuromorphic computing, energy storage, sensors, neural electrodes, and actuators. Conventionally, OMIEC polymers are prepared through chemical, vapor‐phase, electrochemical, or enzymatic polymerization, typically relying on oxidants, metal catalysts, and/or organic solvents, significantly limiting their scalability, sustainability, and biocompatibility. Here, we introduce an initiator‐free, visible‐light‐induced polymerization of water‐soluble conducting polymer precursors, enabling facile formation of high‐performance and inherently biocompatible OMIECs. This novel approach allows direct photopatterning and seamless film deposition and manufacturing of OECTs across rigid, flexible, and biological substrates, exemplified by glass, textiles, and mouse skin (in vivo). Through careful optimization of the photopolymerization process, resulting OMIECs possess state‐of‐the‐art electrical, electrochemical, and device properties along with exceptional compatibility and conformability with various flexible and biological surfaces. Finally, we demonstrate the utility of these photopatterned electrodes, manufactured directly on mouse skin in vivo, where they significantly enhance the recording efficacy and signal‐to‐noise ratio of low‐frequency brain activity in anesthetized mice.

A functionalized polythiophene autonomously produced ∼1 × 10 ⁻⁴ mol H ₂ O ₂ per g polymer (18% doping level) in aqueous O ₂ solutions via ORR. This work opens new applications driven by this process and elucidates degradation mechanisms in OE devices.

Conjugated polymers are widely studied for application areas ranging from energy technology to wearable electronics and bioelectronics. To develop a truly sustainable technology, environmentally benign synthesis is essential. Here, the open-flask synthesis of a multitude of conjugated polymers at room temperature by ambient direct arylation polymerization (ADAP) is demonstrated. The batch synthesis of over 100 grams of polymer in a green solvent and continuous droplet flow synthesis without any solid support is described. Polymers prepared by ADAP are characterized by improved structural order compared to materials prepared by other methods. Hence, organic electrochemical transistors (OECTs) feature beyond state-of-the-art electrical properties, i.e., an OECT hole mobility μ as high as 6 cm ² V ⁻¹ s ⁻¹ , a volumetric capacitance C ^* over 200 F cm ⁻³ , and thus a figure of merit [μ C ^* ] exceeding 1100 F cm ⁻¹ V ⁻¹ s ⁻¹ . Thus, ADAP paves the way for the benign and large-scale production of high-performance conjugated polymers.

The 3D micro- and nanostructure of wood has extensively been employed as a template for cost-effective and renewable electronic technologies. However, other electroactive components, in particular native lignin, have been overlooked due to the absence of an approach that allows access of the lignin through the cell wall. In this study, we introduce an approach that focuses on establishing conjugated-polymer-based electrical connections at various length scales within the wood structure, aiming to leverage the charge storage capacity of native lignin in wood-based energy storage electrodes. We demonstrate that poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) PEDOT/PSS, integrated within the cell wall lumen, can be interfaced with native lignin through the wood cell wall through in situ polymerization of a water-soluble S-EDOT monomer. This approach increases the capacitance of the conductive wood to 315 mF cm-2 at a scan rate of 5 mV s-1, which is seven and, respectively, two times higher compared to the capacitance of conductive wood made with the single components PEDOT/PSS or S-PEDOT. Moreover, we show that the capacitance is contributed by both the electroactive polymers and native lignin, with native lignin accounting for over 70% of the total charge storage capacity. We show that accessing native lignin through in situ creation of electrical interconnections within the wood structure offers a pathway toward sustainable, wood-based electrodes with improved charge-storage capacity for applications in electronics and energy storage.

Organic mixed ionic-electronic conductors are promising materials for interfacing and monitoring biological systems, with the aim of overcoming current challenges based on the mismatch between biological materials and convectional inorganic conductors. The conjugated polymer/polyelectrolyte complex poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT/PSS) is, up to date, the most widely used polymer for in vitro or in vivo measurements in the field of organic bioelectronics. However, PEDOT/PSS organic electrochemical transistors (OECTs) are limited by depletion mode operation and lack chemical groups that enable synthetic modifications for biointerfacing. Recently introduced thiophene-based polymers with oligoether side chains can operate in accumulation mode, and their chemical structure can be tuned during synthesis, for example, by the introduction of hydroxylated side chains. Here, we introduce a new thiophene-based conjugated polymer, p(g₄2T-T)-8% OH, where 8% of the glycol side chains are functionalized with a hydroxyl group. We report for the first time the compatibility of conjugated polymers containing ethylene glycol side chains in direct contact with cells. The additional hydroxyl group allows covalent modification of the surface of polymer films, enabling fine-tuning of the surface interaction properties of p(g₄2T-T)-8% OH with biological materials, either hindering or promoting cell adhesion. We further use p(g₄2T-T)-8% OH to fabricate the OECTs and demonstrate for the first time the monitoring of epithelial barrier formation of Caco-2 cells in vitro using accumulation mode OECTs. The conjugated polymer p(g₄2T-T)-8% OH allows organic-electronic-based materials to be easily modified and optimized to interface and monitor biological systems.