Recent advances in polymer-based thin-film electrodes for ECoG applications

Electrocorticography (ECoG) has garnered widespread attention owing to its superior signal resolution compared to conventional electroencephalogram (EEG). While ECoG signal acquisition entails invasiveness, the invasive rigid electrode used inevitably inflicts damage on brain tissue. Polymer electrodes that combine conductivity and transparency have garnered great interest because they not only facilitate high-quality signal acquisition but also provide additional insights while preserving the health of the brain, positioning them as the future frontier in the brain-computer interface (BCI). This review summarizes the multifaceted functions of polymers in ECoG thin-film electrodes for the BCI. We present the abilities of sensitive and structural polymers focusing on impedance reduction, signal quality improvement, good flexibility, and transparency. Typically, two sensitive polymers and four structural polymers are analyzed in detail in terms of ECoG electrode properties. Moreover, the underlying mechanism of polymer-based electrodes in signal quality enhancement is revealed. Finally, the remaining challenges and perspectives are discussed.

Organic Iono-Optoelectronics: From Electrochromics to Artificial Retina

ConspectusOrganic mixed ionic electronic conductors (OMIECs) represent an exciting and emerging class of materials that have recently revitalized the field of organic semiconductors. OMIECs are particularly attractive because they allow both ionic and electronic transport while retaining the inherent benefits of organic semiconducting materials such as mechanical conformability and biocompatibility. These combined properties make the OMIECs ideal for applications in bioelectronics, energy storage, neuromorphic computing, and electrochemical transistors for sensing. Within the realm of OMIECs, a subset of materials and devices known as organic iono-optoelectronics (OIOEs) further leverage the optoelectronic properties of organic semiconductors and functions based on ionic-electronic-photonic interactions. Ionic-electronic coupling can regulate the bandgap of organic semiconducting materials, allowing the tuning of optical properties, which forms the basis for organic electrochromic technology. Additionally, light, as a form of energy, can modulate ionic-electronic coupling, enabling applications such as machine vision and artificial retina.Among these applications, organic electrochromic devices have demonstrated their practical and commercial value due to their rapid, high-contrast color switching capabilities and potential for cost-effective mass production and roll-to-roll manufacturing. Ambilight Inc. has spearheaded this technology, introducing the first organic electrochromic sunroof product, now used in hundreds of thousands of vehicles. Despite these promising advancements, organic electrochromic devices face several challenges. These include achieving optical contrast higher than 90%, improving color switching speed to meet the demands of dynamic display applications, and enhancing durability to ensure stability in extreme environmental conditions, such as prolonged exposure to sunlight. Growing research on light-modulated ionic-electronic coupling suggests that this fundamental process can be used to mimic the ion-flux-dependent light-capturing processes found in biological retina systems, offering a promising approach for constructing future artificial retina (vision). The intrinsic softness and biocompatibility of the OIOEs further enhance the potential of the artificial retina to interface with biological systems for applications in biomedical optoelectronics and human-machine interfaces. Compared to electrochromic technology, artificial retinas and biomedical optoelectronics are still in their infancy. In this Account, we use two representative technologies─electrochromic devices and artificial retina─to introduce the fundamental processes, advancements, and challenges in the field of OIOEs. We begin with an overview of the fundamental processes shared by and unique to these two technologies. Next, we discuss their respective challenges and the approaches taken by our group and others to improve their performance. Finally, we suggest future research directions. We hope this Account will introduce readers to these fascinating materials and devices and inspire further interest in these research areas.

Organic Mixed Ionic-Electronic Conductors for Bioelectronic Sensors: Materials and Operation Mechanisms

The field of organic mixed ionic-electronic conductors (OMIECs) has gained significant attention due to their ability to transport both electrons and ions, making them promising candidates for various applications. Initially focused on inorganic materials, the exploration of mixed conduction has expanded to organic materials, especially polymers, owing to their advantages such as solution processability, flexibility, and property tunability. OMIECs, particularly in the form of polymers, possess both electronic and ionic transport functionalities. This review provides an overview of OMIECs in various aspects covering mechanisms of charge transport including electronic transport, ionic transport, and ionic-electronic coupling, as well as conducting/semiconducting conjugated polymers and their applications in organic bioelectronics, including (multi)sensors, neuromorphic devices, and electrochromic devices. OMIECs show promise in organic bioelectronics due to their compatibility with biological systems and the ability to modulate electronic conduction and ionic transport, resembling the principles of biological systems. Organic electrochemical transistors (OECTs) based on OMIECs offer significant potential for bioelectronic applications, responding to external stimuli through modulation of ionic transport. An in-depth review of recent research achievements in organic bioelectronic applications using OMIECs, categorized based on physical and chemical stimuli as well as neuromorphic devices and circuit applications, is presented.

Effect of Ligand Chain Length for Tuning of Molecular Dimensionality and Magnetic Relaxation in Redox Active Cobalt(II) EDOT Complexes (EDOT = 3,4-Ethylenedioxythiophene)

Four cobalt(II) complexes, [Co(L1)2(NCX)2(MeOH)2] (X = S (1), Se (2)) and {[Co(L2)2(NCX)2]}n (X = S (3), Se (4)) (L1 = 2,5dipyridyl-3,4,-ethylenedioxylthiophene and L2 = 2,5diethynylpyridinyl-3,4-ethylenedioxythiophene), were synthesized by incorporating ethylenedioxythiophene based redox-active luminescence ligands. All these complexes have been well characterized using single-crystal X-ray diffraction analyses, spectroscopic and magnetic investigations. Magneto-structural studies showed that 1 and 2 adopt a mononuclear structure with CoN4O2 octahedral coordination geometry while 3 and 4 have a 2D [4 x 4] rhombic grid coordination networks (CNs) where each cobalt(II) center is in a CoN6 octahedral coordination environment. Static magnetic measurements reveal that all four complexes displayed a high spin (HS) (S = 3/2) state between 2 and 280 K which was further confirmed by X-band and Q-band EPR studies. Remarkably, along with the molecular dimensionality (0D and 2D) the modification in the axial coligands lead to a significant difference in the dynamic magnetic properties of the monomers and CNs at low temperatures. All complexes display slow magnetic relaxation behavior under an external dc magnetic field. For the complexes with NCS- as coligand observed higher energy barrier for spin reversal in comparison to the complexes with NCSe- as coligand, while mononuclear complex 1 exhibited a higher energy barrier than that of CN 3. Theoretical calculations at the DFT and CASSCF level of theory have been performed to get more insight into the electronic structure and magnetic properties of all four complexes.

Benzotriazole-EDOT electrochromic conjugated polymers perform sub-second response time and 774 cm2C-1 coloration efficiency

To investigate the effect of double fluorine substitution on the optical, electrochemical, thermodynamic, morphological and electrochromic properties of electrochromic polymers, two benzotriazole-EDOT electrochromic conjugated polymers of PBTz-E and P2F-BTz-E were...