The electrochemical doping/dedoping kinetics, and the organic electrochemical transistor (OECT) performance of a series of polythiophene homopolymers with ethylene glycol units in their side chains ...using both kosmotropic and chaotropic anion solutions were studied. We compare their performance to a reference polymer, the polythiophene derivative with diethylene glycol side chains, poly(3-{2-(2-methoxyethoxy)ethoxymethyl}thiophene-2,5-diyl) (P3MEEMT). We find larger OECT material figure of merit,
μC
*, where
μ
is the carrier mobility and
C
* is the volumetric capacitance, and faster doping kinetics with more oxygen atoms on the side chains, and if the oxygen atom is farther from the polythiophene backbone. Replacing the oxygen atom close to the polythiophene backbone with an alkyl unit increases the film π-stacking crystallinity (higher electronic conductivity in the undoped film) but sacrifices the available doping sites (lower volumetric capacitance
C
* in OECT). We show that this variation in
C
* is the dominant factor in changing the
μC
* product for this family of polymers. With more oxygen atoms on the side chain, or with the oxygen atom farther from the polymer backbone, we observe both more passive swelling and higher
C
*. In addition, we show that, compared to the doping speed, the dedoping speed, as measured
via
spectroelectrochemistry, is both generally faster and less dependent on ion species or side chain oxygen content. Last, through OECT, electrochemical impedance spectroscopy (EIS) and spectroelectrochemistry measurements, we show that the chaotropic anion PF
6
−
facilitates higher doping levels, faster doping kinetics, and lower doping thresholds compared to the kosmotropic anion Cl
−
, although the exact differences depend on the polymer side chains. Our results highlight the importance of balancing
μ
and
C
* when designing molecular structures for OECT active layers.
We find larger
μC
* and faster doping kinetics with more oxygen atoms on the side chain, and if the oxygen atom is farther from the polymer backbone. We show that this variation in
C
* is the dominant factor in changing the
μC
* for these polymers.
Aliphatic amine and carboxylic acid ligands are widely used as organic solvents during the bottom-up synthesis of inorganic nanoparticles (NPs). Although the ligands’ ability to alter final NP ...properties has been widely studied, side reactivity of these ligands is emerging as an important mechanism to consider. In this work, we study the thermal decomposition of common ligands with varying functional groups (amines and carboxylic acids) and bond saturations (from saturated to polyunsaturated). Here, we investigate how these ligand properties influence decomposition in the absence and presence of precursors used in NP synthesis. We show that during the synthesis of inorganic chalcogenide NPs (Cu2ZnSnS4, Cu x S, and SnS x ) with metal acetylacetonate precursors and elemental sulfur, the ligand pyrolyzes, producing alkylated graphitic species. Additionally, there was less to no ligand decomposition observed during the sulfur-free synthesis of ZnO and CuO with metal acetylacetonate precursors. These results will help guide ligand selection for NP syntheses and improve reaction purity, an important factor in many applications.
Size exclusion chromatography (SEC) is not well suited for characterizing the molecular weight (MW) and MW distribution of conjugated polymers, especially those that absorb strongly at the detection ...wavelengths, or those that interact with and adsorb on the walls of SEC columns. We demonstrate diffusion-ordered NMR spectroscopy (DOSY) as a complementary method for characterizing the size and size distribution of conjugated polymers. Starting with four batches of poly(3-hexylthiophene), whose distinct and narrow MW distributions had been fully characterized, as a model system, we establish a power-law relationship between the weight-average MW and the diffusion coefficient measured through DOSY. We extend this approach to characterizing poly4-(4,4-dihexadecyl-4H-cyclopenta1,2-b:5,4-b′dithiophen-2-yl)-alt-1,2,5thiadiazolo-3,4-cpyridine, whose absorption properties preclude its characterization with light scattering based techniques, including SEC. By applying the same power law on the diffusion coefficients obtained by DOSY measurements, we extracted P3HT-equivalent MWs and MW distributions for six different batches of PCDTPT. By circumventing the practical issues in SEC measurements, DOSY shows promise as a versatile complement for determining polymer size.
Although extensive efforts have been devoted to understanding electronic transport in conjugated polymers, little is known about their ionic conduction characteristics in relation to polymer ...chemistry, processing, and morphology. This work presents a combined computational and experimental study on morphology and ion transport in thin-film blends of polythiophene derivatives bearing oligoethylene glycol side-chains and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Using molecular dynamics (MD) simulation, we show that in the amorphous phase, the polythiophene derivative P3MEET bearing oligoethylene glycol side-chains with oxygen directly attached to the thiophene rings possesses lower Li+ ionic conductivity compared to its analog P3MEEMT that has a methyl spacer between the oxygen and the thiophene rings. Structural characterization of P3MEET and P3MEEMT thin film upon blending with LiTFSI indicates that adding LiTFSI expands the side-chain domains of the polymer crystallites and reduces the total degree of crystallinity at the same time. Moreover, LiTFSI is found to infiltrate both the amorphous and crystalline regimes at low concentrations but preferably resides in the amorphous domain at high LiTFSI concentrations. Ionic transport measured by electrochemical impedance spectroscopy in both P3MEET- and P3MEEMT-LiTFSI thin films is found to occur predominately in the amorphous domain, and ionic conductivity in P3MEEMT-LiTFSI is always higher than in P3MEET-LiTFSI samples, consistent with predictions from MD simulations. Our work provides a platform to predict and study the influence of polymer chemistry on the ionic conductivity of conjugated polymers.
The efficient synthesis of regioregular poly(3-hexylthiophene-2,5-diyl)s (rr-P3HTs) capped with chalcogens using a simple quenching method is reported. Thiol (SH) end groups are selectively installed ...at the terminating end (ω-end) or at both the initiating (α-) and ω-ends using sulphur powder or triisopropylsilanethiol (TIPS-SH), respectively.
Mixed ion/electron conducting polymers have recently received significant interest from a number of research communities, spanning from biological to mechanical. Their ability to conduct ions and ...electrons in the same material enables their use in a wide range of electrochemical devices. This functionality can be used to improve performance of more traditional devices or enable completely novel ones. Herein the use of blended polymers, block copolymers, and homopolymers as mixed conducting polymer systems is discussed, with special emphasis on connecting polymer structure and morphology to mixed conduction performance. Following this discussion, the outlook for the future of this field is presented.
A review highlighting the implications of morphology on the mixed conduction performance of polymers.
We find that conjugated polymers can undergo reversible structural phase transitions during electrochemical oxidation and ion injection. We study ...poly2,5-bis(thiophenyl)-1,4-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)benzene (PB2T-TEG), a conjugated polymer with glycolated side chains. Using grazing incidence wide-angle X-ray scattering (GIWAXS), we show that, in contrast to previously known polymers, this polymer switches between two structurally distinct crystalline phases associated with electrochemical oxidation/reduction in an aqueous electrolyte. Importantly, we show that this unique phase change behavior has important physical consequences for ion-polaron pair transport. Notably, using moving front experiments visualized by both optical microscopy and super-resolution photoinduced force microscopy (PiFM), we show that a laterally propagating ion-polaron pair front in PB2T-TEG exhibits non-Fickian transport, retaining a sharp step-edge profile, in stark contrast to the Fickian diffusion more commonly observed in polymers like P3MEEMT. This structural phase transition is reminiscent of those accompanying ion uptake in inorganic materials like LiFePO4. We propose that the engineering of similar properties in future conjugated polymers may enable the realization of new materials with superior performance in electrochemical energy storage or neuromorphic memory applications.
Poly(indacenodithiophene-benzothiadiazole) has received significant interest because of its exceptional hole mobility despite its near-amorphous thin-film morphology and brittleness at low M n. In ...comparison, poly(indacenodithiophene-benzopyrollodione) (PIDTBPD) has a lower hole mobility but is exceptionally ductile at similar M n. Herein, we synthesize random indacenodithiophene (IDT) copolymers with varying amounts of incorporated benzothiadiazole and benzopyrollodione (BPD), which introduces varied degrees of backbone twist to each respective polymer system. This allows us to elucidate how the BPD monomer introduction leads to conformational and morphological changes that influence the crack onset strain (CoS) and hole mobility of these near-amorphous IDT copolymers and the rates by which each material property responds to sequentially larger BPD incorporation. Results of density functional theory calculations suggest that BPD introduction does not lead to significant differences in backbone linearity between the studied polymers, and grazing incidence wide-angle X-ray scattering demonstrates that the degree of crystallinity within thin films is not significantly altered. It does, however, lead to a more varied circular distribution of the hexadecyl side chains around the polymer backbone. With increasing BPD incorporation, a crossover point between CoS and hole mobility emerges. At this crossover point, a random copolymer with 30% BPD introduction displays increased CoS and an average hole mobility value equal to that of the PIDTBPD system, suggesting that hole mobility is more sensitive to torsion along the polymer backbone, while the response of the CoS is relatively delayed. The data also suggest that the increase in CoS with increasing BPD content does not arise because of differences in rigidity but because the more circular distribution of the side chains makes polymer chains with sufficient BPD content better able to flow.
Carrier spins in semiconductor nanocrystals are promising candidates for quantum information processing. Using a combination of time-resolved Faraday rotation and photoluminescence spectroscopies, we ...demonstrate optical spin polarization and coherent spin precession in colloidal CsPbBr3 nanocrystals that persists up to room temperature. By suppressing the influence of inhomogeneous hyperfine fields with a small applied magnetic field, we demonstrate inhomogeneous hole transverse spin-dephasing times (T 2 *) that approach the nanocrystal photoluminescence lifetime, such that nearly all emitted photons derive from coherent hole spins. Thermally activated LO phonons drive additional spin dephasing at elevated temperatures, but coherent spin precession is still observed at room temperature. These data reveal several major distinctions between spins in nanocrystalline and bulk CsPbBr3 and open the door for using metal-halide perovskite nanocrystals in spin-based quantum technologies.
Direct arylation is an appealing method for preparing π-conjugated materials, avoiding the prefunctionalization required for traditional cross-coupling methods. A major effort in organic electronic ...materials development is improving the environmental and economic impact of production; direct arylation polymerization (DArP) is an effective method to achieve these goals. Room-temperature polymerization would further improve the cost and energy efficiencies required to prepare these materials. Reported herein is new mechanistic work studying the underlying mechanism of room temperature direct arylation between iodobenzene and indole. Results indicate that room-temperature, Pd/Ag-catalyzed direct arylation systems are radical-mediated. This is in contrast to the commonly proposed two-electron mechanisms for direct arylation and appears to extend to other substrates such as benzo
thiophene and pentafluorobenzene.
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