the operation of a range of bioelectronic devices, [1][2][3] such as organic electrochemical transistors (OECTs), [4][5][6] batteries, [7] and supercapacitors. [6] They have inherent advantages over traditional organic semiconductors for these electrochemical applications, [4,[8][9][10] in particular their ability to operate with an aqueous electrolyte. [11,12] Exchanging a traditional alkyl-based side chain for a glycol-based hydrophilic side chain has been widely adopted as a strategy for increasing uptake of water and ions in OMIECs, and subsequently increasing their capacitance. [5,7,[13][14][15] Whilst polythiophenes bearing long alkyl side chains are often reported to pack with interdigitating side chains [16][17][18][19][20][21][22] and π-stacks that are either straight or lightly tilted [17,20,[22][23][24] (see Figure S1, Supporting Information for backbone packing motifs referred to in this study), little is known about glycolated OMIEC packing, despite the chain packing being critical to both electronic and ionic transport. [21,[25][26][27][28] Experimental studies have suggested that glycolated OMIECs adopt smaller π-stack distances than their alkylated counterparts. [5,29] As well as solid-state packing, structural characterization of OMIECs should account for their swelling behavior, 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 modeling 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 π-stack and through the lamellar stack respectively. Finally, the two distinct ways triethylene glycol polymers can bind to cations are revealed, showing the formation of a metastable single bound state, or an energetically deep double bound state, both with a strong side-chain length dependence. 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.

Conjugated polymers (CPs) that show stable and reversible cation insertion/deinsertion under ambient conditions hold great potential for optoelectronic and energy storage devices. However, n-doped CPs are prone to parasitic reactions upon exposure to moisture or oxygen. This study reports a new family of napthalenediimide (NDI) based conjugated polymers capable of undergoing electrochemical n-type doping in ambient air. By functionalizing the NDI-NDI repeating unit with alternating triethylene glycol and octadecyl side chains, the polymer backbone shows stable electrochemical doping at ambient conditions. We systematically investigate the extent of volumetric doping involving monovalent cations of varying size (Li + , Na + , tetraethylammonium (TEA + )) with electrochemical methods, including cyclic voltammetry, differential pulse voltammetry, spectroelectrochemistry, and electrochemical impedance spectroscopy. We observed that introducing hydrophilic side chains on the polymer backbone improves the local dielectric environment of the backbones and lowers the energetic barrier for ion insertion. Surprisingly, when using Na + electrolyte, the polymer films exhibit higher volumetric doping efficiency, faster-switching kinetics, higher optical contrast, and selective multielectrochromism when compared to Li + or TEA + electrolytes. Using well-tempered metadynamics, we characterize the free energetics of side chain−ion interactions to find that Li + binds more tightly to the glycolated NDI moieties than Na + , hindering Li + ion transport, switching kinetics, and limiting the films' doping efficiency.

Emergent bioelectronic technologies are underpinned by the organic electrochemical transistor (OECT), which employs an electrolyte medium to modulate the conductivity of its organic semiconductor channel.Here we utilize postpolymerization modification (PPM) on a conjugated polymer backbone to directly introduce glycolated or anionic side chains via fluoride displacement. The resulting polymers demonstrated increased volumetric capacitances, with subdued swelling, compared to their parent polymer in ptype enhancement mode OECTs. This increase in capacitance was attributed to their modified side chain configurations enabling cationic charge compensation for thin film electrochemical oxidation, as deduced from electrochemical quartz crystal microbalance measurements. An overall improvement in OECT performance was recorded for the hybrid glycol/ionic polymer compared to the parent, owing to its low swelling and bimodal crystalline orientation as imaged by grazing-incidence wide-angle X-ray scattering, enabling its high charge mobility at 1.02 cm 2 •V −1 •s −1 . Compromised device performance was recorded for the fully glycolated derivative compared to the parent, which was linked to its limited face-on stacking, which hindered OECT charge mobility at 0.26 cm 2 •V −1 •s −1 , despite its high capacitance. These results highlight the effectiveness of anionic side chain attachment by PPM as a means of increasing the volumetric capacitance of p-type conjugated polymers for OECTs, while retaining solid-state macromolecular properties that facilitate hole transport.

Electrochemical reduction of atmospheric oxygen provides carbon emission-free pathways for the generation of electricity from chemical fuels and for the distributed production of green chemical oxidants like hydrogen peroxide. Recently, organic mixed ionic-electronic conducting polymers (OMIECs) have been reported as active electrode materials for the oxygen reduction reaction. This work sets out to identify the operative oxygen reduction mechanism of OMIECs through a multi-faceted experimental and theoretical approach. Using a combination of pH-dependent electrochemical characterization, operando UV-Vis and Raman spectroscopy, ab initio calculations, and steady-state microkinetic simulations, we find that the n-type OMIEC, p(NDI-T2 P75), reduces oxygen selectively to hydrogen peroxide through a non-catalytic, outer-sphere pathway. This pathway serves as a general guide to understand the reactivity of an expanded set of n- and p-type OMIECs investigated in this work and provides a framework to rationalize when (or if) organic compounds function as heterogeneous catalysts for oxygen reduction.

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