Other affiliations: Georgia Institute of Technology, Université libre de Bruxelles, University of Mons-Hainaut
Bio: Vincent Lemaur is an academic researcher from University of Mons. The author has contributed to research in topics: Organic semiconductor & Mass spectrometry. The author has an hindex of 36, co-authored 112 publications receiving 5348 citations. Previous affiliations of Vincent Lemaur include Georgia Institute of Technology & Université libre de Bruxelles.
Papers published on a yearly basis
TL;DR: A comparative transport study of several high-mobility conjugated polymers by field-effect-modulated Seebeck, transistor and sub-bandgap optical absorption measurements is reported, showing that in several of these polymers, the charge transport properties approach intrinsic disorder-free limits at which all molecular sites are thermally accessible.
Abstract: Measurements and simulations of several high-mobility conjugated polymers show that their charge transport properties reflect an almost complete lack of disorder in the polymers, despite their amorphous microstructures, resulting from the resilience of the planar polymer backbone conformations to side-chain disorder. So-called 'conjugated polymers' have attracted much interest in recent decades. They are organic macromolecules with covalent-bond-containing backbone structures that combine the flexibility and processibility of plastics with the useful electronic properties of semiconductors. Polymeric materials tend to be naturally disordered however, and such disorder ultimately limits their electronic performance. Deepak Venkateshvaran and colleagues now show that several of the better-performing conjugated polymers are actually behaving electronically as if they were free of disorder, despite their amorphous microstructure. With the aid of simulations, the authors identify the molecular origins of this surprising 'disorder-free' behaviour, and offer guidelines for how this might be engineered into other conjugated polymeric systems. Conjugated polymers enable the production of flexible semiconductor devices that can be processed from solution at low temperatures. Over the past 25 years, device performance has improved greatly as a wide variety of molecular structures have been studied1. However, one major limitation has not been overcome; transport properties in polymer films are still limited by pervasive conformational and energetic disorder2,3,4,5. This not only limits the rational design of materials with higher performance, but also prevents the study of physical phenomena associated with an extended π-electron delocalization along the polymer backbone. Here we report a comparative transport study of several high-mobility conjugated polymers by field-effect-modulated Seebeck, transistor and sub-bandgap optical absorption measurements. We show that in several of these polymers, most notably in a recently reported, indacenodithiophene-based donor–acceptor copolymer with a near-amorphous microstructure6, the charge transport properties approach intrinsic disorder-free limits at which all molecular sites are thermally accessible. Molecular dynamics simulations identify the origin of this long sought-after regime as a planar, torsion-free backbone conformation that is surprisingly resilient to side-chain disorder. Our results provide molecular-design guidelines for ‘disorder-free’ conjugated polymers.
TL;DR: A significant increase in the charge mobility when going from triphenylene to hexaazatrinaphthylene is predicted; this finding has been confirmed by measurements carried out with the pulse-radiolysis time-resolved microwave conductivity technique.
Abstract: We describe at the quantum-chemical level the main parameters that control charge transport at the molecular scale in discotic liquid crystals. The focus is on stacks made of triphenylene, hexaazatriphenylene, hexaazatrinaphthylene, and hexabenzocoronene molecules and derivatives thereof. It is found that a subtle interplay between the chemical structure of the molecules and their relative positions within the stacks determines the charge transport properties; the molecular features required to promote high charge mobilities in discotic materials are established on the basis of the calculated structure-property relationships. We predict a significant increase in the charge mobility when going from triphenylene to hexaazatrinaphthylene; this finding has been confirmed by measurements carried out with the pulse-radiolysis time-resolved microwave conductivity technique.
TL;DR: It is shown, for instance, that highly symmetric configurations of the complex can strongly limit charge recombination and emphasizes the need for a fine control of the supramolecular organization at organic-organic interfaces in donor-acceptor blends.
Abstract: This work focuses on two fundamental processes in organic solar cellsexciton dissociation and charge recombinationand describes how quantum-chemical calculations can be exploited to estimate the molecular parameters that determine the rates of these processes. The general concepts behind our approach are illustrated by considering a donor−acceptor complex made of a phthalocyanine (electron donor) molecule and a perylene (acceptor) molecule. The results highlight how the relative rates of the two processes depend on the dimensionality of the molecules, their relative positions, the symmetry of the relevant electronic levels, and the polarity of the medium. It is shown, for instance, that highly symmetric configurations of the complex can strongly limit charge recombination; this emphasizes the need for a fine control of the supramolecular organization at organic−organic interfaces in donor−acceptor blends.
TL;DR: In this paper, a kinetic-based structure-activity relationship for quercetin is analyzed by quantum chemical calculations, which support the knowledge acquired from experimental studies, in terms of the nature of the prereaction complexes, the pH, the formation of activated-deprotonated forms, and the atom-and electron-transfer efficiency.
Abstract: Polyphenols (synthetically modified or directly provided by human diet) scavenge free radicals by H-atom transfer and may thus decrease noxious effects due to oxidative stress. Free radical scavenging by polyphenols has been widely theoretically studied from the thermodynamic point of view whereas the kinetic point of view has been much less addressed. The present study describes kinetic-based structure–activity relationship for quercetin. This compound is very characteristic of the wide flavonoid subclass of polyphenols. H-atom transfer is a mechanism based on either atom or electron transfer. This is analyzed here by quantum chemical calculations, which support the knowledge acquired from experimental studies. The competition between the different processes is discussed in terms of the nature of the prereaction complexes, the pH, the formation of activated-deprotonated forms, and the atom- and electron-transfer efficiency. The role of the catechol moiety and the 3-OH group of quercetin as scavengers of ...
TL;DR: A series of π-extended boron- and nitrogen-doped nanographenes are designed as promising candidates for efficient thermally activated delayed fluorescence emitters with concomitantly decreased singlet-triplet energy gaps, improved oscillator strengths and core rigidity compared to previously reported structures, permitting both emission color purity and tunability across the visible spectrum.
Abstract: The work was supported by the European Union’s Horizon 2020 research and innovation program under Grant Agreement N°. 646176 (EXTMOS project). A.P. acknowledges the financial support from the Marie Curie Fellowship (MILORD project, N°. 748042). Computational resources have been provided by the Consortium des Equipements de Calcul Intensif (CECI), funded by the Fonds de la Recherche Scientifiques de Belgique (F.R.S.-FNRS) under Grant No. 2.5020.11, as well as the Tier-1 supercomputer of the Federation Wallonie-Bruxelles, infrastructure funded by the Walloon Region under the grant agreement n1117545. The St Andrews team would like to thank the Leverhulme Trust (RPG-2016-047) and EPSRC (EP/P010482/1) for financial support.
01 May 1993
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.
Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.
28 Jul 2005
TL;DR: Electronic Coupling in Oligoacene Derivatives: Factors Influencing Charge Mobility, and the Energy-Splitting-in-Dimer Method 3.1.
Abstract: 2.2. Materials 929 2.3. Factors Influencing Charge Mobility 931 2.3.1. Molecular Packing 931 2.3.2. Disorder 932 2.3.3. Temperature 933 2.3.4. Electric Field 934 2.3.5. Impurities 934 2.3.6. Pressure 934 2.3.7. Charge-Carrier Density 934 2.3.8. Size/molecular Weight 935 3. The Charge-Transport Parameters 935 3.1. Electronic Coupling 936 3.1.1. The Energy-Splitting-in-Dimer Method 936 3.1.2. The Orthogonality Issue 937 3.1.3. Impact of the Site Energy 937 3.1.4. Electronic Coupling in Oligoacene Derivatives 938
TL;DR: All works discussed in this review aim at demonstrating that Deep Eutectic Solvents not only allow the design of eco-efficient processes but also open a straightforward access to new chemicals and materials.
Abstract: Within the framework of green chemistry, solvents occupy a strategic place. To be qualified as a green medium, these solvents have to meet different criteria such as availability, non-toxicity, biodegradability, recyclability, flammability, and low price among others. Up to now, the number of available green solvents are rather limited. Here we wish to discuss a new family of ionic fluids, so-called Deep Eutectic Solvents (DES), that are now rapidly emerging in the current literature. A DES is a fluid generally composed of two or three cheap and safe components that are capable of self-association, often through hydrogen bond interactions, to form a eutectic mixture with a melting point lower than that of each individual component. DESs are generally liquid at temperatures lower than 100 °C. These DESs exhibit similar physico-chemical properties to the traditionally used ionic liquids, while being much cheaper and environmentally friendlier. Owing to these remarkable advantages, DESs are now of growing interest in many fields of research. In this review, we report the major contributions of DESs in catalysis, organic synthesis, dissolution and extraction processes, electrochemistry and material chemistry. All works discussed in this review aim at demonstrating that DESs not only allow the design of eco-efficient processes but also open a straightforward access to new chemicals and materials.
TL;DR: The focus of this review will be on the performance analysis of π-conjugated systems in OFETs, a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals that provide an important insight into the charge transport of ρconjugate systems.
Abstract: Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear