| 1. |
- Chen, Yongzhen, 1990-, et al.
(författare)
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Experimental and Theoretical Investigation into the Polaron Structure of K-Doped Polyfluorene Films
- 2021
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:1, s. 937-945
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of the electronic structure and optical transition upon n-doping of poly(9,9-dioctylfluorene) (PFO) films is elucidated with photoelectron spectroscopy, optical absorption, density functional theory (DFT), and time-dependent DFT (TD-DFT) calculations. Optical absorption measurements extending into near infrared show two low-energy absorption features at low doping ratios and an additional peak at a higher energy of similar to 2.2 eV that disappears with increasing doping ratios. A gap state (i.e., polaronic state) close to the Fermi level and a significantly destabilized highest valence band appear in the experimentally measured ultraviolet photoelectron spectra. These experimental results are interpreted by the TD-DFT calculations, which show that the lower energy peaks originate from the excitation from polaronic states to the conduction band, while the higher energy peak mainly originates from the destabilized valence band to conduction band transitions and only appears at low doping ratios (c(red) <= 50%, 0.5 potassium atom per fluorene monomer). The DFT calculations further indicate that polaron pairs rather than bipolarons are preferentially formed at high doping ratios. Comparing the results of doped glassy and beta-phase films, we find that the ordered segments in the beta-phase film disappear due to the dopant (potassium) insertion, resulting in a similar polaronic structure.
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| 2. |
- Gerasimov, Jennifer Yevgenia, 1985-, et al.
(författare)
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Rational Materials Design for In Operando Electropolymerization of Evolvable Organic Electrochemical Transistors
- 2022
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Ingår i: Advanced Functional Materials. - : John Wiley and Sons Inc. - 1616-301X .- 1616-3028. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- Organic electrochemical transistors formed by in operando electropolymerization of the semiconducting channel are increasingly becoming recognized as a simple and effective implementation of synapses in neuromorphic hardware. However, very few studies have reported the requirements that must be met to ensure that the polymer spreads along the substrate to form a functional conducting channel. The nature of the interface between the substrate and various monomer precursors of conducting polymers through molecular dynamics simulations is investigated, showing that monomer adsorption to the substrate produces an increase in the effective monomer concentration at the surface. By evaluating combinatorial couples of monomers baring various sidechains with differently functionalized substrates, it is shown that the interactions between the substrate and the monomer precursor control the lateral growth of a polymer film along an inert substrate. This effect has implications for fabricating synaptic systems on inexpensive, flexible substrates. © 2022 The Authors.
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| 3. |
- Ghosh, Sarbani, et al.
(författare)
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Effect of Substrate on Structural Phase Transition in a Conducting Polymer during Ion Injection and Water Intake: A View from a Computational Microscope
- 2020
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Ingår i: ACS APPLIED ELECTRONIC MATERIALS. - : AMER CHEMICAL SOC. - 2637-6113. ; 2:12, s. 4034-4041
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Tidskriftsartikel (refereegranskat)abstract
- Conducting polymers operating in aqueous electrolyte represent mixed electron-ion conductors, where the ion injection and water intake can lead to structural and morphological changes that can strongly affect the material morphology and device performance. In the present paper, using molecular dynamics simulations, we provide an atomistic understanding of the structural phase transitions during electrochemical oxidation and ion injection in a conjugated polymer with glycolated side chains recently reported by Bischak et al. [J. Am. Chem. Soc., 2020, 142, 7434], where the polymer switched between two structurally distinct phases corresponding to different oxidation levels. To outline the structural changes, we calculated the polymer film morphology and X-ray diffraction patterns at different oxidation levels. We demonstrated that the observed phase transition arises due to interplay between several factors, including the effect of the substrate leading to the preferential edge-on arrangement of the chains and formation of lamellas; unzipping of the interdigitated polymer chains during oxidation and ion intake; and changes in the morphology when pi-pi stacking is absent at low oxidation level and forms at the high oxidation level facilitating the electron mobility and enabling the oxidation of the polymer film. Our calculations quantitatively reproduce the experimental data, which outlines the predictive power of the molecular modeling of the polymer systems that can be utilized for the design of materials and devices with improved performance.
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| 4. |
- Ghosh, Sarbani, et al.
(författare)
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Electronic structure, optical properties, morphology and charge transport in naphthalenediimide (NDI)-based n-type copolymer with altered pi-conjugation: A theoretical perspective
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 118:22
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Tidskriftsartikel (refereegranskat)abstract
- Future developments of the thermoelectric technologies based on conducting polymer require to find n-type polymers with performance, especially electrical conductivity, comparable to the one of the state-of-the-art p-type conducting polymers. In this regard, naphthalenediimide based donor-acceptor copolymers have appeared as promising candidates. The backbone of the polymer can be engineered to control the electronic structure and the morphology of the chains in order to maximize both the charge carrier density and mobility. However, at the moment a complete theoretical insight from electronic structures to charge transport is missing. Here, we use a multiscale theoretical framework to study naphthalenediimide based donor-acceptor copolymers where the donor pi-conjugated dithienylvinylene moieties are replaced by pi non-conjugated dithienylethane in various amounts, and we show that this approach is in position to rationalize many experimental data. The resulting gradual change in electronic structure of polymer chains is investigated by the density functional theory and correlated with experimental absorption spectra. The morphology of a polymer film is studied by means of molecular dynamics simulations, showing that an extended network of inter-chain pi-pi stacking is preserved upon introduction of non-conjugated units in the polymer backbone. This finding is supported by a subsequent calculation of the charge transport, which shows only a moderate impact of the morphology on the mobility, while the experimental data can be retrieved by considering the effect of the pi non-conjugated moiety on the electronic structure. Such a multiscale description of conducting polymers paves the way toward fully theoretical design of future high performances materials.
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| 5. |
- Ghosh, Sarbani, et al.
(författare)
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Electronic Structures and Optical Absorption of N-Type Conducting Polymers at Different Doping Levels
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:25, s. 15467-15476
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical understanding of the electronic structure and optical transitions in n-doped conducting polymers is still controversial for polaronic and bipolaronic states and is completely missing for the case of a high doping level. In the present paper, the electronic structure and optical properties of the archetypical n-doped conducting polymer, double-stranded benzimidazo-benzophenanthroline ladder (BBL), are studied using the density functional theory (DFT) and the time dependent DFT method. We find that a polaronic state in the BBL chain is a spin-resolved doublet where the spin degeneracy is lifted. The ground state of two electrons corresponds to a triplet polaron pair, which is in stark contrast to a commonly accepted picture where two electrons are postulated to form a spinless bipolaron. The total spin gradually increases until the reduction level reaches c(red) = 100% (i.e., one electron per monomer unit). With further increase of the reduction level, the total spin decreases until it becomes 0 for the reduction level c(red) = 200%. The calculated results reproduce the experimentally observed spin signal without any phenomenological parameters. A detailed analysis of the evolution of the electronic structure of BBL and its absorption spectra with increase in reduction level is presented. The calculated UV-vis-NIR spectra are compared with the available experimental results. The electronic structure and optical absorption for different reduction levels presented here are generic to a wide class of conducting polymers, which is illustrated by the corresponding calculations for another archetypical conducting polymer, poly(3,4-ethylenedioxythiophene) (best known as PEDOT).
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| 6. |
- Gladisch, Johannes, et al.
(författare)
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Reversible Electronic Solid-Gel Switching of a Conjugated Polymer
- 2020
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Ingår i: ADVANCED SCIENCE. - : WILEY. - 2198-3844. ; 7:2
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Tidskriftsartikel (refereegranskat)abstract
- Conjugated polymers exhibit electrically driven volume changes when included in electrochemical devices via the exchange of ions and solvent. So far, this volumetric change is limited to 40% and 100% for reversible and irreversible systems, respectively, thus restricting potential applications of this technology. A conjugated polymer that reversibly expands by about 300% upon addressing, relative to its previous contracted state, while the first irreversible actuation can achieve values ranging from 1000-10 000%, depending on the voltage applied is reported. From experimental and theoretical studies, it is found that this large and reversible volumetric switching is due to reorganization of the polymer during swelling as it transforms between a solid-state phase and a gel, while maintaining percolation for conductivity. The polymer is utilized as an electroactive cladding to reduce the void sizes of a porous carbon filter electrode by 85%.
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| 7. |
- Heasman, Patrick, et al.
(författare)
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A computational study of cellulose regeneration: All-atom molecular dynamics simulations
- 2023
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Ingår i: Carbohydrate Polymers. - : ELSEVIER SCI LTD. - 0144-8617 .- 1879-1344. ; 311
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Tidskriftsartikel (refereegranskat)abstract
- Processing natural cellulose requires its dissolution and regeneration. It is known that the crystallinity of re-generated cellulose does not match that of native cellulose, and the physical and mechanical properties of re-generated cellulose can vary dependent on the technique applied. In this paper, we performed all-atom molecular dynamics simulations attempting to simulate the regeneration of order in cellulose. Cellulose chains display an affinity to align with one another on the nanosecond scale; single chains quickly form clusters, and clusters then interact to form a larger unit, but the end results still lack that abundance of order. Where aggregation of cel-lulose chains occurs, there is some resemblance of the 1-10 surfaces found in Cellulose II, with certain indication of 110 surface formation. Concentration and simulation temperature show an increase of aggregation, yet it appears that time is the major factor in reclaiming the order of "crystalline" cellulose.
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| 8. |
- Lacas, Benjamin, et al.
(författare)
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Role of radiotherapy fractionation in head and neck cancers (MARCH) : an updated meta-analysis
- 2017
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Ingår i: The Lancet Oncology. - 1470-2045 .- 1474-5488. ; 18:9, s. 1221-1237
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Tidskriftsartikel (refereegranskat)abstract
- Background The Meta-Analysis of Radiotherapy in squamous cell Carcinomas of Head and neck (MARCH) showed that altered fractionation radiotherapy is associated with improved overall and progression-free survival compared with conventional radiotherapy, with hyperfractionated radiotherapy showing the greatest benefit. This update aims to confirm and explain the superiority of hyperfractionated radiotherapy over other altered fractionation radiotherapy regimens and to assess the benefit of altered fractionation within the context of concomitant chemotherapy with the inclusion of new trials. Methods For this updated meta-analysis, we searched bibliography databases, trials registries, and meeting proceedings for published or unpublished randomised trials done between Jan 1, 2009, and July 15, 2015, comparing primary or postoperative conventional fractionation radiotherapy versus altered fractionation radiotherapy (comparison 1) or conventional fractionation radiotherapy plus concomitant chemotherapy versus altered fractionation radiotherapy alone (comparison 2). Eligible trials had to start randomisation on or after Jan 1, 1970, and completed accrual before Dec 31, 2010; had to have been randomised in a way that precluded prior knowledge of treatment assignment; and had to include patients with non-metastatic squamous cell carcinoma of the oral cavity, oropharynx, hypopharynx, or larynx undergoing first-line curative treatment. Trials including a non-conventional radiotherapy control group, investigating hypofractionated radiotherapy, or including mostly nasopharyngeal carcinomas were excluded. Trials were grouped in three types of altered fractionation: hyperfractionated, moderately accelerated, and very accelerated. Individual patient data were collected and combined with a fixed-effects model based on the intention-to-treat principle. The primary endpoint was overall survival. Findings Comparison 1 (conventional fractionation radiotherapy vs altered fractionation radiotherapy) included 33 trials and 11 423 patients. Altered fractionation radiotherapy was associated with a significant benefit on overall survival (hazard ratio [HR] 0·94, 95% CI 0·90–0·98; p=0·0033), with an absolute difference at 5 years of 3·1% (95% CI 1·3–4·9) and at 10 years of 1·2% (−0·8 to 3·2). We found a significant interaction (p=0·051) between type of fractionation and treatment effect, the overall survival benefit being restricted to the hyperfractionated group (HR 0·83, 0·74–0·92), with absolute differences at 5 years of 8·1% (3·4 to 12·8) and at 10 years of 3·9% (−0·6 to 8·4). Comparison 2 (conventional fractionation radiotherapy plus concomitant chemotherapy versus altered fractionation radiotherapy alone) included five trials and 986 patients. Overall survival was significantly worse with altered fractionation radiotherapy compared with concomitant chemoradiotherapy (HR 1·22, 1·05–1·42; p=0·0098), with absolute differences at 5 years of −5·8% (−11·9 to 0·3) and at 10 years of −5·1% (−13·0 to 2·8). Interpretation This update confirms, with more patients and a longer follow-up than the first version of MARCH, that hyperfractionated radiotherapy is, along with concomitant chemoradiotherapy, a standard of care for the treatment of locally advanced head and neck squamous cell cancers. The comparison between hyperfractionated radiotherapy and concomitant chemoradiotherapy remains to be specifically tested. Funding Institut National du Cancer; and Ligue Nationale Contre le Cancer.
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| 9. |
- Moser, Maximilian, et al.
(författare)
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Controlling Electrochemically Induced Volume Changes in Conjugated Polymers by Chemical Design : from Theory to Devices
- 2021
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; n/a:n/a
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemically induced volume changes in organic mixed ionic-electronic conductors (OMIECs) are particularly important for their use in dynamic microfiltration systems, biomedical machinery, and electronic devices. Although significant advances have been made to maximize the dimensional changes that can be accomplished by OMIECs, there is currently limited understanding of how changes in their molecular structures impact their underpinning fundamental processes and their performance in electronic devices. Herein, a series of ethylene glycol functionalized conjugated polymers is synthesized, and their electromechanical properties are evaluated through a combined approach of experimental measurements and molecular dynamics simulations. As demonstrated, alterations in the molecular structure of OMIECs impact numerous processes occurring during their electrochemical swelling, with sidechain length shortening decreasing the number of incorporated water molecules, reducing the generated void volumes and promoting the OMIECs to undergo different phase transitions. Ultimately, the impact of these combined molecular processes is assessed in organic electrochemical transistors, revealing that careful balancing of these phenomena is required to maximize device performance.
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| 10. |
- Moser, Maximilian, et al.
(författare)
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Side Chain Redistribution as a Strategy to Boost Organic Electrochemical Transistor Performance and Stability
- 2020
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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