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Self-doping organic semiconductors provide a promising route to avoid instabilities and morphological issues associated with molecular n-type dopants. Structural characterization of a naphthalenetetracarboxylic diimide (NDI) semiconductor covalently bound to an ammonium hydroxide group is presented. The dopant precursor was found to be the product of an unexpected base catalyzed hydrolysis, which was reversible. The reversible hydrolysis had profound consequences on the chemical composition, morphology, and electronic performance of the doped films. In addition, we investigated the degradation mechanism of the quaternary ammonium group and the subsequent doping of NDI. These findings reveal that the products of more than one chemical reaction during processing of films must be considered when utilizing this promising class of water-soluble semiconductors.

Conjugated polymers achieve redox activity in electrochemical devices by combining redox-active, electronically conducting backbones with ion-transporting side chains that can be tuned for different electrolytes. In aqueous electrolytes, redox activity can be accomplished by attaching hydrophilic side chains to the polymer backbone, which enables ionic transport and allows volumetric charging of polymer electrodes. While this approach has been beneficial for achieving fast electrochemical charging in aqueous solutions, little is known about the relationship between water uptake by the polymers during electrochemical charging and the stability and redox potentials of the electrodes, particularly for electron-transporting conjugated polymers. We find that excessive water uptake during the electrochemical charging of polymer electrodes harms the reversibility of electrochemical processes and results in irreversible swelling of the polymer. We show that small changes of the side chain composition can significantly increase the reversibility of the redox behavior of the materials in aqueous electrolytes, improving the capacity of the polymer by more than one order of magnitude. Finally, we show that tuning the local environment of the redox-active polymer by attaching hydrophilic side chains can help to reach high fractions of the theoretical capacity for single-phase electrodes in aqueous electrolytes. Our work shows the importance of chemical design strategies for achieving high electrochemical stability for conjugated polymers in aqueous electrolytes.

Exchanging hydrophobic alkyl-based side chains to hydrophilic glycol-based side chains is a widely adopted method for improving mixed-transport device performance, despite the impact on solid state packing and polymer-electrolyte interactions being poorly understood. Presented here is a Molecular Dynamics (MD) force field for modelling alkoxylated and glycolated polythiophenes. The force field is validated against known packing motifs for their monomer crystals. MD simulations, coupled with X-ray Diffraction (XRD), show that alkoxylated polythiophenes will pack with a `tilted stack' and straight interdigitating side chains, whilst their glycolated counterpart will pack with a `deflected stack' and an s-bend side chain configuration. MD simulations reveal water penetration pathways into the alkoxylated and glycolated crystals - through the {\pi}-stack and through the lamellar stack respectively. Finally, the two distinct ways tri-ethylene glycol polymers can bind to cations are revealed, showing the formation of a meta-stable single bound state, or an energetically deep double bound state, both with a strong side chain length dependance. The minimum energy pathways for the formation of the chelates are identified, showing the physical process through which cations can bind to one or two side chains of a glycolated polythiophene, with consequences for ion transport in bithiophene semiconductors., Comment: 10 pages, 4 figures

Donor-acceptor (D-A) polymers are promising materials for organic electrochemical transistors (OECTs), as they minimize detrimental faradaic side-reactions during OECT operation, yet their steady-state OECT performance still lags far behind their all-donor counterparts. Here, we report three D-A polymers based on the diketopyrrolopyrrole unit that afford OECT performances similar to those of all-donor polymers, hence representing a significant improvement to the previously developed D-A copolymers. In addition to improved OECT performance, DFT simulations of the polymers and their respective hole polarons also revealed a positive correlation between hole polaron delocalization and steady-state OECT performance, providing new insights into the design of OECT materials. More importantly, we demonstrate how polaron delocalization can be tuned directly at the molecular level by selection of the building blocks comprising the polymers' conjugated backbone, thus paving the way for the development of even higher performing OECT polymers.

© Copyright 2019 American Chemical Society. Organic electrochemical transistors (OECTs) composed of organic mixed conductors can operate in aqueous, biological media and translate low-magnitude ionic fluctuations of biological origin into measurable electrical signals. The growing technological interest in these biotransducers makes the fundamental understanding of ion-to-electron coupling extremely important for the design of new materials and devices. One crucial aspect in this process that has been so far disregarded is the water taken up by the film during device operation and its effects on device performance. Here, using a series of the same electrolyte with varying ion concentrations, we quantify the amount of water that is incorporated into a hydrophilic p-type organic semiconductor film alongside the dopant anions and investigate structural and morphological changes occurring in the film upon electrochemical doping. We show that infiltration of the hydrated dopant ions into the film irreversibly changes the polymer structure and negatively impacts the efficiency, reversibility, and speed of charge generation. When less water is injected into the channel, OECTs exhibit higher transconductance and faster switching speeds. Although swelling is commonly suggested to be a necessity for efficient ion-to-electron transduction, this work uncovers the negative impact of a swollen channel material on the performance of accumulation mode OECTs and lays the foundation for future materials design.

Rapid and efficient measurement of sodium ion concentrations will benefit future studies and healthcare due to the importance of sodium to many biological processes. Ratiometric optical probes, where light absorption wavelengths shift according to ion concentration, can be used as a quick measurement method. In contrast to the currently available UV absorbing probes, we have synthesised a series of sensors which absorb in different regions of the visible spectrum. In addition to measurement by conventional UV-Vis spectroscopy, this also enables analysis of sodium ion concentration from colorimetry, opening the door to faster and cheaper analysis. Finally, the optical properties of the dyes were well reproduced by computational methods, with and without the presence of sodium, enabling acceleration of design of future materials.

A series of glycolated polythiophenes for use in organic electrochemical transistors (OECTs) is designed and synthesized, differing in the distribution of their ethylene glycol chains that are tethered to the conjugated backbone. While side chain redistribution does not have a significant impact on the optoelectronic properties of the polymers, this molecular engineering strategy strongly impacts the water uptake achieved in the polymers. By careful optimization of the water uptake in the polymer films, OECTs with unprecedented steady-state performances in terms of [mu C*] and current retentions up to 98% over 700 electrochemical switching cycles are developed. Funding Agencies|KAUSTKing Abdullah University of Science & Technology; King Abdullah University of Science and Technology Office of Sponsored Research (OSR) [OSR-2018-CARF/CCF-3079, OSR-2015-CRG4-2572, OSR-4106 CPF2019]; EC FP7 Project SC2 [610115]; EC H2020 [643791]; EPSRCEngineering & Physical Sciences Research Council (EPSRC) [EP/G037515/1, EP/M005143/1, EP/L016702/1]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Wallenberg Wood Science Center [KAW 2018.0452]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University [2009-00971]; TomKat Center for Sustainable Energy at Stanford University

Conjugated polymers are promising engineering tools for establishing bilateral electrical communication with living systems. The free energy of their films, the roughness, and charge density play major roles in determining their interactions with lipid bilayers, which form the membrane barrier around every living cell allowing for molecular exchange with the extracellular environment. In this work, we investigate lipid bilayer formation from synthetic lipid vesicles (liposomes) on a series of amphiphilic copolymer films based on naphthalene 1,4,5,8 tetracarboxylic diimide bithiophene (NDI-T2) backbone where the alkyl side chain is gradually exchanged for an ethylene glycol-based side chain. As the concentration of ethylene glycol in the composition changes, the surface energy of the films varies drastically, which, in turn, effects the interactions with liposomes. By imaging the interactions of fluorophore-labeled liposomes with these surfaces via a fluorescence microscope, we show that the films can be cast such that ethylene glycol-rich regions, which liposomes favor, are accumulated on the surface and extract information on the wettability behavior that has not been possible using other surface sensitive techniques. This approach uncovers the solid/liquid interface of a promising class of electron transporting conjugated polymer films and suggests synthetic strategies to maximize the number of lipid-polymer contacts for the formation of supported lipid bilayers.

The lipid bilayer is the elemental structure of a cell membrane, forming a stable barrier between the interior and exterior of the cell while hosting membrane proteins that enable selective transport of biologically important compounds and cellular recognition. Monitoring the quality and function of lipid bilayers is thus essential and can be performed using electrically active substrates that allow for transduction of signals. Such a promising electronic transducer material is the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) which has provided a plethora of novel bio transducing architectures. The challenge is, however, in assembling a bilayer on the conducting polymer surface, which is defect-free and has high mobility. Herein, we investigate the fusion of zwitterionic vesicles not only on a variety of PEDOT:PSS films, but also on an electron transporting, negatively charged organic semiconductor, in order to understand the surface properties that trigger vesicle fusion. The PEDOT:PSS films are prepared from dispersions containing different concentrations of ethylene glycol included as a formulation additive, which gives a handle to modulate the surface physicochemical properties without a compromise on the chemical composition. A strong correlation between the polarity of the surface, the fusion of the vesicles and the mobility of the resulting bilayer aids in extracting the design principles for the development of future conducting polymers that will enable the formation of lipid bilayers.

We report the development of redox-active conjugated polymers with potential application to electrochemical energy storage. Side chain engineering enables processing of the polymer electrodes from solution, stability in aqueous electrolytes and efficient transport of ionic and electronic charge carriers. We synthesized a 3,3' dialkoxybithiophene homo polymer (p type polymer) with glycol side chains and prepared naphthalene 1,4,5,8-tetracarboxylic-diimide-dialkoxybithiophene (NDI gT2) copolymers (n type polymer) with either a glycol or zwitterionic side chain on the NDI unit. For the latter, we developed a post-functionalization synthesis to attach the polar zwitterion side chains to the polymer backbone to avoid challenges of purifying polar intermediates. We demonstrate fast and reversible charging of solution processed electrodes for both the p- and n type polymers in aqueous electrolytes, without using additives or porous scaffolds and for films up to micrometers thick. We apply spectroelectrochemistry as an in operando technique to probe the state of charge of the electrodes. This reveals that thin films of the p-type polymer and zwitterion n-type polymer can be charged reversibly with up to two electronic charges per repeat unit (bipolaron formation). We combine thin films of these polymers in a two-electrode cell and demonstrate output voltages of up to 1.4 V with high redox stability. Our findings demonstrate the potential of functionalizing conjugated polymers with appropriate polar side chains to improve specific capacity, reversibility and rate capabilities of polymer electrodes in aqueous electrolytes., Main text 16 pages including 6 figures + 49 pages of supporting information. arXiv admin note: substantial text overlap with arXiv:1711.10457

In article number https://doi.org/10.1002/advs.201901144, Eleni Stavrinidou, Magnus Berggren, and co‐workers present a conjugated polymer that exhibits unprecedented volume change when electrochemically addressed. The thiophene‐based polymer expands between 1000% and 10 000% irreversibly and 300% reversibly when oxidized. Molecular Dynamics reveal that the polymer transforms between a solid state to gelled state upon redox switching.

With a host of new materials being investigated as active layers in organic electrochemical transistors (OECTs), several advantageous characteristics can be utilized to improve transduction and circuit level performance for biosensing applications. Here, the subthreshold region of operation of one recently reported high performing OECT material, poly(2‐(3,3′‐bis(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)‐[2,2′‐bithiophen]‐5‐yl)thieno[3,2‐b]thiophene), p(g2T‐TT) is investigated. The material's high subthreshold slope (SS) is exploited for high voltage gain and low power consumption. An ≈5× improvement in voltage gain (A V) for devices engineered for equal output current and 370× lower power consumption in the subthreshold region, in comparison to operation in the higher transconductance (g m), superthreshold region usually reported in the literature, are reported. Electrophysiological sensing is demonstrated using the subthreshold regime of p(g2T‐TT) devices and it is suggested that operation in this regime enables low power, enhanced sensing for a broad range of bioelectronic applications. Finally, the accessibility of the subthreshold regime of p(g2T‐TT) is evaluated in comparison with the prototypical poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and the role of material design in achieving favorable properties for subthreshold operation is discussed.

This is the first ever demonstration of an accumulation mode OECT for biosensing and n-type polymer in electrocatalysis., The inherent specificity and electrochemical reversibility of enzymes poise them as the biorecognition element of choice for a wide range of metabolites. To use enzymes efficiently in biosensors, the redox centers of the protein should have good electrical communication with the transducing electrode, which requires either the use of mediators or tedious biofunctionalization approaches. We report an all-polymer micrometer-scale transistor platform for the detection of lactate, a significant metabolite in cellular metabolic pathways associated with critical health care conditions. The device embodies a new concept in metabolite sensing where we take advantage of the ion-to-electron transducing qualities of an electron-transporting (n-type) organic semiconductor and the inherent amplification properties of an ion-to-electron converting device, the organic electrochemical transistor. The n-type polymer incorporates hydrophilic side chains to enhance ion transport/injection, as well as to facilitate enzyme conjugation. The material is capable of accepting electrons of the enzymatic reaction and acts as a series of redox centers capable of switching between the neutral and reduced state. The result is a fast, selective, and sensitive metabolite sensor. The advantage of this device compared to traditional amperometric sensors is the amplification of the input signal endowed by the electrochemical transistor circuit and the design simplicity obviating the need for a reference electrode. The combination of redox enzymes and electron-transporting polymers will open up an avenue not only for the field of biosensors but also for the development of enzyme-based electrocatalytic energy generation/storage devices.

We report a design strategy that allows the preparation of solution processable n type materials from low boiling point solvents for organic electrochemical transistors (OECTs). The polymer backbone is based on NDI-T2 copolymers where a branched alkyl side chain is gradually exchanged for a linear ethylene glycol based side chain. A series of random copolymers are prepared with glycol side chain percentages of 0, 10, 25, 50, 75, 90 and 100 with respect to the alkyl side chains. These are characterized in order to study the influence of the polar side chains on interaction with aqueous electrolytes, their electrochemical redox reactions and performance in OECTs when operated in aqueous electrolytes. We observe that glycol side chain percentages of >50 % are required to achieve volumetric charging while lower glycol chain percentages show a mixed operation with high required voltages to allow for bulk charging of the organic semiconductor. A strong dependence of the electron mobility on the fraction of glycol chains was found for copolymers based on NDI-T2, with a significant drop as alkyl side chains are replaced by glycol side chains.

N-doping of conjugated polymers either requires a high dopant fraction or yields a low electrical conductivity because of their poor compatibility with molecular dopants. We explore n doping of the polar naphthalenediimide-bithiophene copolymer p(gNDI-gT2) that carries oligoethylene glycol-based side chains and show that the polymer displays superior miscibility with the benzimidazole-dimethylbenzenamine-based n-dopant N-DMBI. The good compatibility of p(gNDI-gT2) and N-DMBI results in a relatively high doping efficiency of 13% for n-dopants, which leads to a high electrical conductivity of more than 10(-1) S cm(-1) for a dopant concentration of only 10 mol % when measured in an inert atmosphere. We find that the doped polymer is able to maintain its electrical conductivity for about 20 min when exposed to air and recovers rapidly when returned to a nitrogen atmosphere. Overall, solution coprocessing of p(gNDI-gT2) and N-DMBI results in a larger thermoelectric power factor of up to 0.4 mu W K-2 m(-1) compared to other NDI-based polymers.

A novel dibenzoylmethane-fullerene e,e,e-tris adduct was synthesized by the application of a variation of the Bingel–Hirsch conditions and characterized among others by X-ray crystallography. In addition, the corresponding hexakis adduct was detected by MALDI-TOF-MS analysis. Its existence was supported by density-functional-theory (DFT) computations. Furthermore a new synthesis of bis(benzoyl)methanofullerene was established, and its molecular structure was elucidated by X-ray crystallography. DFT computations reproduced the experimentally determined conformation and predict a low energy barrier for the rotation of the two benzoyl moieties.