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Abstract The design of polymeric semiconductors exhibiting high electrical conductivity (σ) and thermoelectric power factor (PF) will be vital for flexible large‐area electronics. In this work, four polymers based on diketopyrrolopyrrole (DPP), 2,3‐dihydrothieno[3,4‐b][1,4]dioxine (EDOT), thieno[3,2‐b]thiophene (TT), and 3, 3′‐bis (2‐(2‐(2‐methoxyethoxy) ethoxy) ethoxy)‐2, 2′‐bithiophene (MEET) are investigated as side‐chains, with the MEET polymers newly synthesized for this study. These polymers are systematically doped with tetrafluorotetracyanoquinodimethane ( F₄TCNQ), CF3SO3H, and the synthesized dopant Cp(CN)₃‐(COOMe)₃, differing in geometry and electron affinity. The DPP‐EDOT‐based polymer containing MEET as side‐chains exhibits the highest conductivity (σ) ≈700 S cm−1 in this series with the acidic dopant (CF₃SO₃H). This polymer also shows the lowest oxidation potential by cyclic voltammetry (CV), the strongest intermolecular interactions evidenced by differential scanning calorimetry (DSC), and has the most oxygen‐based functionality for possible hydrogen bonding and ionic screening. Other polymers exhibit high σ ≈300–500 S cm−1 and power factor up to 300 µW m⁻¹K⁻². The mechanism of conductivity is predominantly electronic, as validated by time‐dependent conductance studies and transient thermo voltage monitoring over time, including for those doped with the acid. These materials maintain significant thermal stability and air stability over ≈6 weeks. Density functional theory calculations reveal molecular geometries and inform about frontier energy levels. Raman spectroscopy, in conjunction with scanning electron microscopy (SEM‐EDS) and x‐ray diffraction, provides insight into the solid‐state microstructure and degree of phase separation of the doped polymer films. Infrared spectroscopy enables this study to further quantify the degree of charge transfer from polymer to dopant. 

We investigated the enhanced vapor responses and altered response ratios of a series of thiophene (co)polymers with oxygenated side chains (CH 2 OH, linear polyethylene glycol, and crown ether), including the novel poly(3-hydroxymethylthiophene) (PTOH) and other newly synthesized polymers. Hydroxymethyl-containing copolymers had higher mobility compared to poly(3-hexylthiophene) (P3HT). The larger crown ether moiety promotes transistor characteristics of P3HT while the smaller one impairs them. Incorporating different oxygen bearing functionalities increased responses of thiophene polymers to NO 2 , NH 3 , and acetone. For example a polyether side chain increases the NO 2 response sensitivity of copolymers of both P3HT and PTOH, but sensitivity towards gas analytes was more prominent for glycol-based functionalities rather than the crown ethers. PTOH is very sensitive to NO 2 and the response likely includes a contribution from conductive protons on the OH group. The lack of correlation among the rank-ordered gas sensitivities imparted by each functional group was found to be useful for designing a selective sensor array. We specifically showed high classification accuracy for all the polymer responses to NO 2 and acetone vapors, both of which gave increased device currents but with response ratios different enough to allow highly classifying discriminant functions to be derived. 

Polythiophenes with differently functionalized side chains (alkyl, oligoethylene oxide, ester, hydroxy, and carboxylic acid) and varied counterions of potassium salt electrolytes were investigated in organic electrochemical transistors (OECTs). In addition, mixed blends were investigated to evaluate any synergistic effects between functionalities. Depending on the functional moiety attached, a large shift to lower potentials of Vth, an increase in drain current, and increase in transconductance can be observed compared to the base combination of alkyl side chain and Cl-. The newly designed and synthesized hydroxy polymer displayed stability to large shifts in VTH, slight increase in drain current, and little or no increase in transconductance when an ionic radius of the dopant is increased until a much larger anion, large polarizability, and low hydration number such as TSFI- was used. The acid-functionalized polymer, on the other hand had the same magnitude in shift with respect to any anion that is larger than Cl-. The polymers were characterized by spectroscopy, x-ray diffraction, thermal analysis, and cyclic voltammetry. This work demonstrates that side-chain engineering can have substantial difference in the level of interaction in the electrolyte which would require tailoring the ion for specific polymer interactions. 

A carboxylated thiophene polymer-based chemiresistive device in a field-effect transistor (FET) configuration with unusual and enhanced responses to the widespread pollutants nitrogen dioxide (NO 2 ) and ammonia (NH 3 ) is described. The device based on a polymeric thiophene carboxylic acid showed a dramatic and superlinear increase in drain current ( I D ) of over 15 000% to a ramped exposure to 10 ppm NO 2 over several minutes, while its ethyl ester counterpart had significantly lower response. Devices incorporating either an ester or carboxylic acid displayed comparable and previously unreported increases in I D from 10 ppm ramped NH 3 exposure of 200–300%. Conventional poly(alkylthiophenes) showed the expected current decreases from similar NH 3 exposures. Using threshold voltage shifts in silicon transistors coupled to our recently reported remote gate (RG) platform with thiophene polymer coatings, we determined that two differing response mechanisms are associated with the two gas exposures. By calculating the charge density induced in the polymers by NO 2 exposure using the silicon transistor voltage shifts, we conclude that proton conduction contributes significantly to the high sensitivity of the carboxylic acid to NO 2 , in addition to doping that was observed for all four polymers. Furthermore, hydrogen bonding moieties of the carboxylic acid and ester may be able to physisorb NH 3 and thus alter the charge distribution, rearrange polymer chains, and/or create a proton transfer network leading to the I D increase that is the opposite of the response obtained from non-carboxylated thiophene polymers. 

Abstract The sensing properties of poly 3‐(3‐carboxypropyl) thiophene‐2,5‐diyl (PT‐COOH) and hydroxylated polythiophene (PT‐OH) as bioreceptor layers were studied and are discussed in this paper. The polymer films cover the channel region of the OECT devices and anti‐human IgG was immobilized on the polymer films. We use threshold voltage (Vth) change as a sensing signal to detect the interaction between anti‐human IgG and human IgG. By adding different concentrations of human IgG, Vth difference can be observed on anti‐human IgG immobilized polymer films, with optimized detection from a blend of the two polymers. Open circuit potential (OCP) measurement was also done on the OECT devices based on the same anti‐human IgG and human IgG interaction pair to help us understand the mechanism behind the antibody functionalization and the interaction between antibody and antigen. Importantly, the observed positive OCP change for the PT‐OH system was self‐consistent with the negative OECT Vth change that was obtained, since the latter is applied to the gate while the former is measured at the channel.