Degree Of Fluorination Research Articles

Surprising behaviour of M–CO(lone pair)⋯π(arene) interactions in the solid state of fluorinated oxaphosphirane complexes

We report the synthesis and X-ray characterization of several oxaphosphirane tungsten(0) complexes especially designed to analyse the intramolecular W–CO(lone pair)⋯π(arene) interaction. The unexpected behaviour of this interaction in the solid state of oxaphosphirane complexes with different degrees of fluorination is rationalized by means of DFT calculations using orbital analysis and Bader's theory of “atoms-in-molecules”.

Influence of fluorination in π-extended backbone polydiketopyrrolopyrroles on charge carrier mobility and depth-dependent molecular alignment

The degree of fluorination in π-extended polydiketopyrrolopyrroles is correlated with semiconductor properties in transistors and an improved molecular alignment in thin films using depth-dependent grazing incidence X-ray scattering.

New heterometallic Ir(III)2-Eu(III) complexes: white light emission from a single molecule.

The design of a relatively simple bifunctional ligand led to the obtainment of three new Ir(III)2-Eu(III) heterometallic complexes. Variation of the degree of fluorination in the cyclometalating ligands coordinated to the Ir(III) centres allows tuning of the photophysical properties and pure white light emission from a single complex.

High thermal stability solution-processable narrow-band gap molecular semiconductors.

A series of narrow-band gap conjugated molecules with specific fluorine substitution patterns has been synthesized in order to study the effect of fluorination on bulk thermal stability. As the number of fluorine substituents on the backbone increase, one finds more thermally robust bulk structures both under inert and ambient conditions as well as an increase in phase transition temperatures in the solid state. When integrated into field-effect transistor devices, the molecule with the highest degree of fluorination shows a hole mobility of 0.15 cm(2)/V·s and a device thermal stability of >300 °C. Generally, the enhancement in thermal robustness of bulk organization and device performance correlates with the level of C-H for C-F substitution. These findings are relevant for the design of molecular semiconductors that can be introduced into optoelectronic devices to be operated under a wide range of conditions.

The Effect of Fluorination in Manipulating the Nanomorphology in PTB7:PC71BM Bulk Heterojunction Systems

The best performing low bandgap copolymers PTB series to date which is based on thieno[3,4‐b]thiophene‐alt‐benzodithiophene units blended with [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM), have been the focus of polymer‐based solar cells. Here, novel fluorinated polymers PTB7‐Fx (fluorine units coupled with submonomer thieno[3,4‐b]thiophene) with varied degree of fluorination are used as electron donor materials. The PTB7‐Fx:PC71BM bulk heterojunction (BHJ) films spin‐coated from the host solvent chlorobenzene without and with solvent additive 1,8‐diiodooctane (DIO) and the corresponding solar cell devices are systematically investigated to address the morphology‐efficiency relationship. Self‐assembled BHJ morphology is already observed for as‐spun blend films. After adding the solvent additive DIO, the pronounced ordered structures are suppressed and better intermixed films with much smaller domain sizes result. Full fluorination of the third C‐atom of thienothiophene gives rise to the highest power conversion efficiency. As the absorption properties, film morphology and crystallinity remain similar for different degrees of fluorination, the main influence of the photovoltaic performance is ascribed to the different lowest unoccupied molecular orbital (LUMO) of each polymer instead of the film morphology. Thus the device performance can be efficiently improved by tuning the energy level of the polymer without necessarily changing either the film nanomorphology or crystallinity dramatically.

Multifunctional TiO2‐Based Particles: The Effect of Fluorination Degree and Liquid Surface Tension on Wetting Behavior

A systematic investigation into the influence of the degree of fluorination on the static and dynamic wetting behavior of TiO2‐based nanobelt (TNB) particles with various liquids is described. The effect of the degree of fluorination and the surface tension of the liquid on the occurrence and stability of liquid marbles, foams or dispersions are studied and the wetting behavior and arrangement of particles at the air–liquid surface are observed. Using contact angle (θ) measurements, the relation between the type of particle‐stabilized material and θ is established. For liquids of relatively high tension like water or formamide which do not wet the fluorinated particles, a powder‐like material (marble) is formed. For polar oils of intermediate tension (35–50 mN m−1), which partially wet the fluorinated particles, stable air‐in‐oil foams can be prepared in which particles form a close‐packed layer enveloping air bubbles. Liquids of relatively low tension, e.g., ethanol or polydimethylsiloxane, wet the particles forming a uniform dispersion and partial sedimentation. By contrast, the as‐prepared hydrophilic TNB particles are rapidly wetted by all the liquids as expected due to their high surface energy. The stable cross‐stacked TNB particles with fluoroalkylsilane (FAS) modification could be a versatile platform in a wide range of applications, especially for fluidic devices (e.g., biofluids, gas sensing, and lab‐on‐a‐chip devices). In a proof‐of‐concept study, the oil–water separation performance of fabrics with chemically stable TNB/FAS coating and the liquid isolation by a TNB/FAS shell for highly sensitive gas sensing or reagent assays are investigated.

Effect of the fluorination degree of hydrophobic chains on the monolayer behavior of unsaturated diacylphosphatidylcholines bearing partially fluorinated 9-octadecynoyl (stearoloyl) groups at the air–water interface

The effect of the fluorination degree of hydrophobic chains on the monolayer behavior of unsaturated diacylphosphatidylcholines (PCs) was examined by employing a series of PCs bearing partially fluorinated 9-octadecynoyl (stearoloyl) groups (DFnStPCs, n: the number of fluorinated carbon atoms in a stearoloyl group; n=1, 2, 4, 8), including their hydrophobic parts – partially fluorinated stearolic acids (FnStAs) – at the air–water interface. π–A isotherm measurements and Brewster angle microscope observations revealed: (i) all DFnStPCs including FnStAs form monolayers of liquid character at 25°C; (ii) they form more expanded monolayers than their non-fluorinated counterparts, distearoloyl-PC (DStPC) and stearolic acid, while the monolayer stability increases with n; (iii) compared with DStPC and DF8StPC, DFnStPCs (n=1, 2, 4) in the low-π region tend to show a weakening in their self-aggregation property and an increase in the work required for monolayer compression; (iv) although DF8StPC forms the most expanded monolayer, the behavior of DF8StPC resembles that of DStPC rather than that of DFnStPCs (n=1, 2, 4). The monolayer behavior of DFnStPCs (n=1, 2, 4) is explained by postulating a flatly-lying conformation of hydrophobic chains, in which three polar parts (ester group, triple bond, CF2CH2 linkage) in chains are immersed in the subphase at large areas. DStPC and DF8StPC lacking a CF2CH2 linkage, however, do not likely adopt such a conformation.

Fluorination of graphene enhances friction due to increased corrugation.

The addition of a single sheet of carbon atoms in the form of graphene can drastically alter friction between a nanoscale probe tip and a surface. Here, for the first time we show that friction can be altered over a wide range by fluorination. Specifically, the friction force between silicon atomic force microscopy tips and monolayer fluorinated graphene can range from 5-9 times higher than for graphene. While consistent with previous reports, the combined interpretation from our experiments and molecular dynamics simulations allows us to propose a novel mechanism: that the dramatic friction enhancement results from increased corrugation of the interfacial potential due to the strong local charge concentrated at fluorine sites, consistent with the Prandtl-Tomlinson model. The monotonic increase of friction with fluorination in experiments also demonstrates that friction force measurements provide a sensitive local probe of the degree of fluorination. Additionally, we found a transition from ordered to disordered atomic stick-slip upon fluorination, suggesting that fluorination proceeds in a spatially random manner.

Photoswitching Azobenzene Derivatives in Single Molecule Junctions: A Theoretical Insight into the I/V Characteristics

The I/V characteristics of several photoswitching azobenzene derivatives connected to two gold electrodes to form single-molecule junctions are investigated within the nonequilibrium Green’s function formalism coupled to density functional theory. We focus here on the changes in the I/V characteristics as a function of the length and degree of fluorination of the conjugated backbones as well as different coupling strength at the electrodes (chemisorption versus physisorption) upon trans/cis isomerization. The calculations illustrate that the conductance is larger for the trans isomer when the molecule is chemisorbed at both electrodes. However, a larger conduction for the cis isomer is found in the presence of a physisorbed contact at one electrode for specific geometries of the isomer in the junction, in full consistency with the apparent discrepancies observed among experimental measurements. The I/V curves are fully rationalized by analyzing the evolution under bias of the shape of the transmitting mol...

Examples of Catalytic and Selective Routes for Fluorinated Building Blocks

Examples are presented for the catalytic fluorination of chlorinated starting materials in order to produce building blocks or HFCs. The fluorination of CF3CH2Cl, of CCl2═CCl2, of trichloromethoxylbenzenes and trichloromethoxybenzene involving nucleophilic substitution are reported. In all cases, HF was the fluorinating agent. Depending on the chlorinated substrate and the degree of fluorination required, liquid- or gas-phase processes were involved. Usually, catalysts were SbCl5 in liquid phase and chromium oxide in gas phase. In the presence of SbCl5, at 90 °C under an initial pressure of 10 bar, the fluorination of CCl2═CCl2 leads mainly to the formation of CClF2CHCl2, and the active catalyst is an antimony mixed halide (SbCl3F2). In the same way, the presence of SbCl5 favored the formation of 1-trifluoromethyl-3-trichloromethylbenzene from bis-1,3-trichloromethylbenzene at low temperature (50 °C) and in the presence of a low amount of HF. Moreover, trichloromethoxybenzene was totally transformed into ...

Decorating tetrathiafulvalene (TTF) with fluorinated phenyls through sulfur bridges: facile synthesis, properties, and aggregation through fluorine interactions.

Tetrathiafulvalene derivatives (TTF1-TTF9) bearing fluorinated phenyl groups attached through the sulfur bridges have been synthesized by employing a copper-mediated C-S coupling reaction of C6 H5-x Fx I (x=1, 2, 5) and a zinc-thiolate complex, (TBA)2 [Zn(DMIT)2 ] (TBA=tetrabutyl ammonium, DMIT=1,3-dithiole-2-thione-4,5-dithiolate), as the key step. Particularly, the selective synthesis of C6 F5 -substituted (TTF8) and C6 F4 -fused (TTF9) TTFs from C6 F5 I is disclosed. The physicochemical properties and crystal structures of these TTFs are fully investigated by UV/Vis absorption spectra, cyclic voltammetry, molecular orbital calculation, and single-crystal X-ray diffraction. The exchange of hydrogen versus fluorine on the peripheral phenyl groups show a notable influence on both the electronic and crystallographic natures of the resulting TTFs: 1) lowering both the HOMO and the LUMO energy levels, 2) modulating the electrochemical properties by regioselective and/or the degree of fluorination, 3) enhancing the driving forces of stacking by multiple fluorine interactions (F⋅⋅⋅S, CF⋅⋅⋅π/πF , CF⋅⋅⋅FC, and CF⋅⋅⋅H). This work indicates that the decoration with fluorinated phenyls holds promise to produce functional TTFs with novel electronic and aggregation features.

Influence of Fluorination and Molecular Weight on the Morphology and Performance of PTB7:PC71BM Solar Cells

The device performance and microstructure of a series of PTB7-based polymers with varied molecular weight and degree of fluorination are investigated. Although the energy level of the highest occupied molecular orbital is found to increase with degree of fluorination, a strong relative molecular weight dependence of device performance dominates any underlying fluorination-dependent trend on overall performance. Microstructural investigation using a combination of X-ray techniques reveals a striking effect of polymer molecular characteristics on film morphology, with the size of PC71BM domains systematically decreasing with increasing polymer molecular weight. Furthermore, the relative purity of the mixed PTB7:PC71BM domain is found to systematically decrease with increasing molecular weight. When domain sizes with and without the use of the solvent additive diiodooctane (DIO) are compared, the effectiveness of DIO in reducing PC71BM domain sizes is also found to be strongly dependent on the molecular weig...

Melting of Partially Fluorinated Graphene: From Detachment of Fluorine Atoms to Large Defects and Random Coils

The melting of fluorographene is very unusual and depends strongly on the degree of fluorination. For temperatures below 1000 K, fully fluorinated graphene (FFG) is thermo-mechanically more stable than graphene but at T$_m\approx$2800 K FFG transits to random coils which is almost twice lower than the melting temperature of graphene, i.e. 5300 K. For fluorinated graphene (PFG) up to 30 % ripples causes detachment of individual F-atoms around 2000 K while for 40-60 % fluorination, large defects are formed beyond 1500 K and beyond 60% of fluorination F-atoms remain bonded to graphene until melting. The results agree with recent experiments on the dependence of the reversibility of the fluorination process on the percentage of fluorination.

Simulation of chemical modification of polymer surface

The mathematical model describing chemical interaction of a polymer film with a reagent gas is developed. This model allows for significant changes in the chemical composition, structure, and physicochemical properties of the polymer as a result of modification. For certain types of surface modification, such as fluorination, a number of limitations and assumptions may be drawn that make it possible to perform the analytical solution of equations which are used as a basis to calculate the depths and profiles of equal fluorination degrees for various amorphous–crystalline polymers. The results of calculations of fluorination degrees conducted within the framework of the model are in fairly good agreement with the experimental data. The effects of surface layer transformed via fluorination on certain important characteristics of films and articles manufactured from polyethylene of various brands are revealed. These effects include increase in the chemical resistance of pipes, decrease in their permeability for low-molecular-mass compounds, reduction in fuel penetration of fuel tanks, and improvement in the thermal compatibility of films.

Photothermally controlled structural switching in fluorinated polyene-graphene hybrids.

Fluorination of graphene enables tuning of its electronic properties, provided that control of the fluorination degree and of modification of graphene structure can be achieved. In this work we demonstrate that SF6 modulated plasma fluorination of monolayer graphene yields polyene-graphene hybrids. The extent of fluorination is determined by the plasma exposure time and controlled in real time by monitoring the change in the optical response by spectroscopic ellipsometry. Raman spectroscopy reveals the formation of polyenes in partially fluorinated graphene (F/C < 0.25), which are responsible for changes in conductivity and for opening a transport gap of ∼25 meV. We demonstrate that the cis- and trans-isomers of the polyenes in graphene are tunable using the photothermal switching. Specifically, the room temperature fluorination results in the cis-isomer that can be converted to the trans-isomer by annealing at T > 150 °C, whereas photoirradiation activates the trans-to-cis isomerization. The two isomers give to the polyene-graphene hybrids different optical and conductivity properties providing a way to engineer electrical response of graphene.

First principles study of fluorinated boron-carbon sheets

Based on the first principles, we investigate the structures and electronic properties of fluorinated BC3, BC5, and BC7. Through the fluorination of BC structure, boron-carbon sheets are more stable than the hydrogenation. The results show that the system becomes semiconductor only on condition that the boron atoms can be bonded with the carbon atoms, whereas, the whole system will become the conductor when all atoms participate in the bonding. With the variation of fluorination degrees, semiconductor-metal transitions appear in the BC3 compounds and metal-semiconductor-metal transitions appear in the BC5 and BC7 sheet. Theoretical analyses find that pz orbital of boron atoms plays an important role in the electronic transition. Because of the rich electronic properties, this kind of fluorinated boron-carbon compound will become potential nanoelectronic materials and our results can play a role in guiding experiments.

Fluorinated Copper(I) Carboxylates as Advanced Tunable p‐Dopants for Organic Light‐Emitting Diodes

Volatile copper(I) benzoates with variable degrees of fluorination are used for p-doping of organic hole-transport layers in single-carrier devices, charge-generation layers, and in organic light-emitting diodes. The charge-transport abilities of the doped materials correlate with the degree and position of the fluorination on the aromatic ring of the carboxylate groups.

Work function modification of the (111) gold surface covered by long alkanethiol-based self-assembled monolayers

Many recent experimental studies have demonstrated that the deposition of self-assembled monolayers on a metal electrode can significantly modulate its work function and hence charge injection properties in organic-based devices. In this context, we model here by means of Density Functional Theory (DFT) calculations the deposition of long saturated and partially fluorinated alkanethiol chains on the gold (111) surface and explore the shift in the work function while changing the size and degree of fluorination of the molecular backbone in order to contribute to the definition of design rules. Among all the derivatization schemes, only the introduction of a terminal fluoromethyl unit leads to an appreciable change in the work function shift, further accompanied by a reversal of its sign. The results show pronounced odd-even effects with different origins.

Effects of Fluorination on Surface Charge Accumulation and Decay of Polyimide Film

In this paper, we present a study aimed at clarifying the effects of fluorination time on surface charge accumulation and decay behaviors of fluorinated polyimide films. The samples were surface-fluorinated in a laboratory vessel at about 328 K using a F2/N2 mixture with 20% F2 by volume at 0.05 MPa for 15, 30, 45, and 60 min. Corona charging tests were performed at room temperature with a relative humidity of ∼40%. The chemical composition of the fluorinated layer of the samples was observed. The results indicate that charge density and charge decay rate are markedly affected by fluorination and that the degree of fluorination is affected by treatment duration.

Synthesis and Evaluation of l-Rhamnose 1C-Phosphonates as Nucleotidylyltransferase Inhibitors

We report the synthesis of a series of phosphonates and ketosephosphonates possessing an L-rhamnose scaffold with varying degrees of fluorination. These compounds were evaluated as potential inhibitors of α-D-glucose 1-phosphate thymidylyltransferase (Cps2L), the first enzyme in Streptococcus pneumoniae L-rhamnose biosynthesis, and a novel antibiotic target. Enzyme-substrate and enzyme-inhibitor binding experiments were performed using water-ligand observed binding via gradient spectroscopy (WaterLOGSY) NMR for known sugar nucleotide substrates and selected phosphonate analogues. IC50 values were measured and Ki values were calculated for inhibitors. New insights were gained into the binding promiscuity of enzymes within the prokaryotic L-rhamnose biosynthetic pathway (Cps2L, RmlB-D) and into the mechanism of inhibition for the most potent inhibitor in the series, L-rhamnose 1C-phosphonate.