Branched Oligo(ether) Side Chains: A Path to Enhanced Processability and Elevated Conductivity for Polymeric Semiconductors

Abstract

conjugated polymers (CPs) with tunable electronic properties will remain a challenge without adequate solution processability due to the importance of techniques such as roll-to-roll manufacturing. Consequently, modifying CP backbones with polar side chains has recently resurged as an attractive structural design approach to improve polymer solubility and to provide CPs with the capability of transporting both electrons and ions, which is crucial for applications such as organic electrochemical transistors (OECTs). Here, a new dioxythiophene copolymer comprised of 2, 2'-bis-(3,4-ethylenedioxy)thiophene (biEDOT) and 3,4-propylenedioxythiophene (ProDOT) substituted with branched oligo(ether) side chains (PE 2 -biOE2OE3) is synthesized using two direct hereto(arylation) polymerization (DHAP) techniques. The typical DHAP technique results in a lower molecular weight polymer (PE 2 -biOE2OE3(L)), which is soluble in acetone and demonstrated a solid-state conductivity after oxidative doping of 55 ± 3 S cm −1 . Alternatively, a unique temperature ramp DHAP methodology results in a higher molecular weight polymer (PE 2 -biOE2OE3(H)) with an especially high solidstate conductivity of 430 ± 60 S cm −1 . Notably, the first OECT fabricated from an acetone-processed polymer is reported, which is stable up to 500 cycles and can provide a pathway for future material design aimed at eliminating the use of toxic chlorinated solvents in OECT active layer processing.

Probing Comonomer Selection Effects on Dioxythiophene-Based Aqueous-Compatible Polymers for Redox Applications

“…Solution UV–vis spectra measured at 0.02 mg/mL in chloroform and thin-film spectra of films deposited on ITO/glass via spray-casting are shown in Figure S5. We note some absorbance in the P­(OE3)-E solution and thin-film spectra above 700 nm, which has been previously attributed to polaron absorption arising from partial polymer oxidation in air. , We confirmed this phenomenon, as chemical reduction of the polymer solution with 1 μL aliquots of hydrazine resulted in an increase in the intensity of the π–π* transition and a depletion of the polaron peak (Figure S6). From the solution UV–vis profiles of the fully reduced P­(OE3) series (Figure a), wherein P­(OE3)-E was treated with hydrazine, we observe that the spectra of P­(OE3)-E and P­(OE3)-Ph are red-shifted relative to P­(OE3)-D. Additionally, we note that P­(OE3)-Ph has pronounced vibronic features consistent with previously published PheDOT-copolymer spectra. , To reduce the spray-cast polymer samples, the P­(OE3) thin films were electrochemically conditioned in 0.5 M NaCl/H 2 O at 50 mV/s for 10 cycles (see experimental Electrochemical Conditioning Section) and then held at −0.7 V versus Ag/AgCl for 30 s to ensure that each polymer was in their electrochemically reduced states (Figure b) .…”

“…After electrochemical conditioning (10 cycles), all three polymers retained up to 90% of their conditioned-film redox capacity after 1000 cycles, suggesting that these materials have a level of stability comparable to other high-performing materials. 53 As these values are consistent with our initial study of the P(OE3)-D polymer, 29 the data suggest that incorporation of the EDOT and PheDOT units do not impair/ impact redox stability. Last, capacitance values were extracted from the cyclic voltammograms run at 50 mV/s in both aqueous and organic electrolytes (Table 2).…”

“…We note some absorbance in the P(OE3)-E solution and thin-film spectra above 700 nm, which has been previously attributed to polaron absorption arising from partial polymer oxidation in air. 53,54 We confirmed this phenomenon, as chemical reduction of the polymer solution with 1 μL aliquots of hydrazine resulted in an increase in the intensity of the π−π* transition and a depletion of the polaron peak (Figure S6). From the solution UV−vis profiles of the fully reduced P(OE3) series (Figure 1a), wherein P(OE3)-E was treated with hydrazine, we observe that the spectra of P(OE3)-E and P(OE3)-Ph are red-shifted relative to P(OE3)-D. Additionally, we note that P(OE3)-Ph has pronounced vibronic features consistent with previously published PheDOT-copolymer spectra.…”

The effect of side chain engineering on conjugated polymers in organic electrochemical transistors for bioelectronic applications

“…37,75,80,81 Introducing branching is an efficient solution to alleviate the processing conditions of these materials. 82,83 Jones et al , has recently reported an acetone-processable CP, PE 2 -biOE2OE3 , that could be readily applied as a OECT channel material, with the chemical structure shown in Fig. 12.…”

“…12 . 82 Upon the electrochemical potential, the loss of the initial channel current is only 10% after 1000 cycles. Similarly, Kang et al , exploit the benefit of branched EG side chains and synthesised a series of water/ethanol processable CPs with a high hole mobility of 0.1 cm 2 V −1 s −1 in the dry state.…”