Degree Of Fluorination Research Articles

Different Modes of Deformation of Soft Triangular Honeycombs at the Sub-5nm Scale.

Patterning on the sub-5nm length scale is a contemporary challenge for further miniaturization of microelectronic circuits. Here, the first soft self-assembled triangular patterns are reported showing transitions between regular and two different kinds of isosceles (acute and obtuse angled) triangles on this length scale, formed by liquid crystalline honeycombs of polyphilic block molecules involving a fluorinated oligo(para-phenylene ethynylene) core. The type of formed triangular pattern depends on the degree and position of fluorination and on temperature. They are the first soft honeycombs combining tilted and nontilted organizations in a uniform nanostructure, where the tilted molecules in only one or two sides of the triangular prismatic cells dominate the shape and the size of the morphology.

Not All Fluorination Is the Same: Unique Effects of Fluorine Functionalization of Ethylene Carbonate for Tuning Solid-Electrolyte Interphase in Li Metal Batteries.

Li metal batteries (LMBs) are crucial for electrifying transportation and aviation. Engineering electrolytes to form desired solid-electrolyte interphase (SEI) is one of the most promising approaches to enable stable long-lasting LMBs. Among the liquid electrolytes explored, fluoroethylene carbonate (FEC) has seen great success in leading to desirable SEI properties for enabling stable cycling of LMBs. Given the many facets to desirable SEI properties, numerous descriptors and mechanisms have been proposed. To build a detailed mechanistic understanding, we analyze varying degrees of fluorination of the same prototype molecule, chosen to be ethylene carbonate (EC) to tease out the interfacial reactivity at the Li metal/electrolyte. Using density functional theory (DFT) calculations, we study the effect of mono-, di-, tri-, and tetra-fluorine substitutions of EC on its reactivity with Li surface facets in the presence and absence of Li salt. We find that the formation of LiF at the early stage of SEI formation, posited as a desirable SEI component, depends on the F-abstraction mechanism rather than the number of fluorine substitution. The best illustrations of this are cis- and trans-difluoro ECs, where F-abstraction is spontaneous with the trans case, while the cis case needs to overcome a nonzero energy barrier. Using a Pearson correlation map, we find that the extent of initial chemical decomposition quantified by the associated reaction free energy is linearly correlated with the charge transferred from the Li surface and the number of covalent-like bonds formed at the surface. The effect of salt and the surface facet have a much weaker role in determining the decompositions at the immediate electrolyte/electrode interfaces. Putting all of this together, we find that tetra-FEC could act as a high-performing SEI modifier as it leads to a more homogeneous, denser LiF-containing SEI. Using this methodology, future investigations will explore -CF3 functionalization and other backbone molecules (linear carbonates).

Direct fluorination of acetyl and ethyl celluloses in perfluorinated liquid medium

Direct fluorination of acetyl- and ethylcelluloses was performed in a bubble reactor with liquid perfluorinated medium (perfluorodecalin). Concentrated fluorination mixtures (F2 + N2) and long reaction times (up to 3 h) were used for better control of the degree of fluorination than it was made previously in direct gaseous fluorination of polymers. The fluorine consumption in the runs with both polymers only slightly increased with increasing temperature and fluorine concentration in the gas mixture. Fluorine content in the fluorinated polymers did not depend strongly on the fluorination conditions. X-ray analysis, differential scanning calorimetry of the fluorinated samples showed no significant changes in respect of the initial polymers. However, emergence of novel and splitting of initial absorption bands, the change of polarization of C–O bonds in IR spectra for the fluorinated samples were observed. It can directly and indirectly justify the appearance of the C–F bonds in the side groups and glycopyranosyl ring of the fluorinated substituted celluloses.19F, 13C solid NMR spectroscopy of the fluorinated samples confirm hydrogen-substituted fluorination of methyl groups.

Chemiresistive Properties of Imprinted Fluorinated Graphene Films.

The electrical conductivity of graphene materials is strongly sensitive to the surface adsorbates, which makes them an excellent platform for the development of gas sensor devices. Functionalization of the surface of graphene opens up the possibility of adjusting the sensor to a target molecule. Here, we investigated the sensor properties of fluorinated graphene films towards exposure to low concentrations of nitrogen dioxide NO2. The films were produced by liquid-phase exfoliation of fluorinated graphite samples with a composition of CF0.08, CF0.23, and CF0.33. Fluorination of graphite using a BrF3/Br2 mixture at room temperature resulted in the covalent attachment of fluorine to basal carbon atoms, which was confirmed by X-ray photoelectron and Raman spectroscopies. Depending on the fluorination degree, the graphite powders had a different dispersion ability in toluene, which affected an average lateral size and thickness of the flakes. The films obtained from fluorinated graphite CF0.33 showed the highest relative response ca. 43% towards 100 ppm NO2 and the best recovery ca. 37% at room temperature.

Density functional theory study of perfluorooctane sulfonate adsorption on fluorinated graphene

Density functional theory calculations are carried out to explore the adsorption behaviour of perfluorooctane sulfonate (PFOS) on pristine and fluorinated graphene. Then, the effects of different degrees of fluorination of graphene on the adsorption of PFOS are systematically investigated by analysis of the adsorption energy (E ads), electron transfer and partial density of states. Finally, the unique adsorption behaviour of PFOS on graphene and fluorinated graphene is demonstrated by a companion study of four other organic molecules, namely hepta-fluorobutyric acid, phenanthrene, phenol and perfluorooctanoate.

How the fluorographene replaced graphene as nanoadditive for improving tribological performances of GTL-8 based lubricant oil

Fluorographene, a new alternative to graphene, it not only inherits the 2-dimensional (2D) layered structure and outstanding mechanical properties, but also possesses controllable C–F bonds. It is meaningful to reveal the evolution processes of the tribological behaviors from graphene to fluorographene. In this work, fluorinated reduced graphene oxide nanosheets (F–rGO) with different degree of fluorination were prepared using direct gas-fluorination and they were added into gas to liquid-8 (GTL-8) base oil as lubricant additive to improve the tribological performance. According to the results, the coefficient of friction (COF) reduced by 21%, notably, the wear rate reduced by 87% with the addition of highly fluorinated reduced graphene oxide (HF–rGO) compared with rGO. It was confirmed that more covalent C–F bonds which improved the chemical stability of HF–rGO resisted the detachment of fluorine so the HF–rGO nanosheets showed less damage, as demonstrated via X-ray photoelectron spectroscopy (XPS), Raman spectra, and transmission electron microscopy (TEM). Meanwhile, the ionic liquid (IL) adsorbed on HF–rGO successfully improved the dispersibility of F–rGO in GTL-8 base oil. The investigation of tribofilm by TEM and focused ion beam (FIB) illustrated that IL displayed a synergy to participate in the tribochemical reaction and increased the thickness of tribofilm during the friction process.

On the Impact of the Degree of Fluorination on the ORR Limiting Processes within Iron Based Catalysts: A Model Study on Symmetrical Films of Barium Ferrate.

In this study, symmetrical films of BaFeO2.67, BaFeO2.33F0.33 and BaFeO2F were synthesized and the oxygen uptake and conduction was investigated by high temperature impedance spectroscopy under an oxygen atmosphere. The data were analyzed on the basis of an impedance model designed for highly porous mixed ionic electronic conducting (MIEC) electrodes. Variable temperature X-ray diffraction experiments were utilized to estimate the stability window of the oxyfluoride compounds, which yielded a degradation temperature for BaFeO2.33F0.33 of 590 °C and a decomposition temperature for BaFeO2F of 710 °C. The impedance study revealed a significant change of the catalytic behavior in dependency of the fluorine content. BaFeO2.67 revealed a bulk-diffusion limited process, while BaFeO2.33F0.33 appeared to exhibit a fast bulk diffusion and a utilization region δ larger than the electrode thickness L (8 μm). In contrast, BaFeO2F showed very area specific resistances due to the lack of oxygen vacancies. The activation energy for the uptake and conduction process of oxygen was found to be 0.07/0.29 eV (temperature range-dependent), 0.33 eV and 0.67 eV for BaFeO2.67, BaFeO2.33F0.33 and BaFeO2F, respectively.

Electrochemical synthesis of fluorinated graphene nanoplatelets in electrolytes containing hydrofluoric acid and TiO2 nanoparticles

In this study, the simultaneous fluorination and exfoliation of graphite by the electrochemical method was studied. The anodic exfoliation of graphite rods in two electrolytes of 10 wt% hydrofluoric acid (HF) and 10 wt% HF + 2.5 g/l TiO2 was carried out by applying various voltages (2.5, 5 and 10 V). The morphological and structural analysis of prepared powders were studied using field emission electron microscopy (FESEM) images, energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy and Fourier-transform infrared (FTIR) spectroscopy. Results indicated that by applying higher voltages, the graphene sheets with a lower number of layers were formed. FTIR spectroscopy and EDS analysis showed the successful fluorination of the graphene with the electrochemical process in both electrolytes. The Raman spectroscopy findings showed that the defect density as well as the degree of fluorination of graphene were decreased by increasing the applied voltages. The related mechanisms for fluorination and exfoliation of graphite were presented in this research.

Occupied and Unoccupied Levels of Half-Fluorinated and Perfluorinated Rubrene Thin Films Probed by One- and Two-Photon Photoemission

We measured occupied and unoccupied energy levels of half-fluorinated and perfluorinated rubrenes (C42F14H14, F14-RUB, and C42F28, PF-RUB) thin films prepared on a highly oriented pyrolytic graphite substrate by a combination of one- and two-photon photoemission spectroscopies. It is revealed that the energy levels near the Fermi level (EF) decrease when the fluorination degree increases, where the energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are located at EF – 1.83 eV and EF + 0.9 eV for F14-RUB and EF – 2.51 eV and EF + 0.6 eV for PF-RUB, respectively. The HOMO–LUMO gaps corresponding to the energy for the creation of free photocarriers in molecular films—known as “transport gaps”—are evaluated by 2.7 eV for F14-RUB and 3.1 eV for PF-RUB.

How Does the Fluorination of the Linker Affect the Structural Chemistry of Trimesate‐Based Metal‐Organic Frameworks (MOFs)?

FMOFs, i.e. metal‐organic frameworks with linkers with fluoro substituents, were supposed to show enhanced thermal and chemical stability as well as high gas affinity and hydrophobicity. However, at least for aromatic carboxylate ligands it was shown in a subsequent work that fluoro substituents weaken the C(phenyl)‐COO– bond and thus facilitate decarboxylation leading to a decreased chemical and thermal stability. Nonetheless, it was concluded that linker fluorination leads to a rich structural chemistry, as the torsion angle between the phenyl ring and the carboxylate group is significantly increased in these compounds. Here, we present the very first examples of four MOFs all based on Sr2+ cations and trimesate‐based linkers with three different degrees of fluorination as well as the known non‐fluorinated counterpart: [Sr(HL)(H2O)]·n H2O [1: L = mF‐BTC3–, n = 0.5, P1, Z = 2; 2: L = dF‐BTC3–, n = 0.5, C2/c, Z = 8; 3: L = pF‐BTC3–, n = 1.5, C2/c, Z = 8; 4: L = BTC3–, n = 0.5, P1, Z = 2; BTC3– ≡ 1,3,5‐benzenetricarboxylate (trimesate); mF‐BTC3– ≡ monofluorinated trimesate, dF‐BTC3– ≡ difluorinated trimesate, pF‐BTC3– ≡ per‐(tri‐)fluorinated trimesate]. Whereas 1 and known 4 are found to crystallize in isotypic structures and 2 in a very similar structural arrangement [all CN(Sr2+) = 9], 3 with the highest degree of fluorination exhibits a completely different crystal structure [CN(Sr2+) = 8], which is already obvious from the different composition. It is shown that the torsion angles between the phenyl ring and the carboxylate groups play an important structure‐directing role. DSC/TGA investigations confirm that with increasing fluorination the thermal stability is decreased. However, the release temperature of water, i.e. the affinity to water, increases with the number of fluoro substituents.

Formation of Ion Pairs and Charge-Transfer Complexes in the p-Doping of Organic Semiconductors

The formation of ion pairs (IPA) through integer charge transfer and ground-state charge-transfer complexes (CPXs) with only fractional charge transfer are the two known mechanisms in the molecular doping of conjugated polymers and molecules, which form the material class of organic semiconductors (OSCs). As it entails no immediate ionization of the OSC, CPX formation is regarded as detrimental to the doping efficiency. For IPA formation to occur, a match between the electron affinity (EA) of the p-dopant and the ionization energy (IE) of the OSC is expected as crucial, while their pronounced frontier molecular orbital overlap should promote CPX formation instead [1].To explore these complementary scenarios, we first studied the thermal de-doping of the prototypical conjugated polymer poly(3-hexylthiophene) (P3HT), p-doped with the common strong electron acceptor tetrafluoro-tetracyanoquinodimethane (F4TCNQ) [2]. We combined grazing incidence X-ray diffraction (GIXRD) with Fourier-transform infrared spectroscopy (FTIR) to determine the microstructure, and absorbance spectroscopy (UV/vis/NIR) to observe the spectral fingerprint of the two doping scenarios. We found two microstructural environments through their distinguished thermal stabilities, where, the dopants were observed (i) alternatingly stacked with the polymer backbone as well as (ii) dispersed in its sidechain region. From FTIR and UV/vis/NIR we deduce that all dopants are fully ionized, although packing between dopant and polymer backbone would be expected to favor CPX formation instead. Notably, while characteristic shifts of the mid-infrared cyano-stretch modes of TCNQ derivatives are known to well indicate the degree of charge transfer, we show here that they allow further to assess the dopant site in the polymer environment.We further investigated the influence of EA with respect to IE by contrasting F4TCNQ with its derivatives of lower degree of fluorination, which translates into reduced EA while leaving the spatial aspects of the dopant largely intact. We find that using F2TCNQ and FTCNQ still results in IPA formation in spite of EA < IE, which we understand through the lower degree of spatial, and therefore energetic order in OSCs as compared to inorganic semiconductors, which therefore possess no sharp band edges. Surprisingly, at high doping concentrations (additional) CPX formation occurred for all the differently strong dopants, which highlights the complexity of these systems going beyond the sole impact of the energetics of the individual constituents.Finally, we juxtaposed the known tendency of small molecular OSCs to form CPXs and that of polymer OSCs to form IPAs. To maximize the comparability with P3HT, alkylated oligothiophenes of different length were synthesized in-house (from 4 to 10 thiophene repeat units) and doped with F4TCNQ. For the longest oligomer, we were able to observe the switch from the CPX regime into that of IPA, i.e., we approach the doping behavior polymer limit. Knowing this threshold is valuable for applications in organic electronics where vacuum processible small molecular OSCs are preferred over polymeric OSCs, which are only processible via solution-based methods.[1] I. Salzmann, G. Heimel, M. Oehzelt, S. Winkler, N. Koch, Acc. Chem. Res. 2016, 49, 370.[2] H. Hase, K. O’Neill, J. Frisch, A. Opitz, N. Koch, I. Salzmann, The Journal of Physical Chemistry C 2018, 122, 25893.

Dissecting terminal fluorinated regulator of liquid crystals for fine-tuning intermolecular interaction and molecular configuration

Intermolecular interaction and molecular configuration are of great importance to the formation of liquid crystals (LCs). In this study, we have designed a fluorinated regulator at the end of LC molecules to investigate mesomorphic properties. Dissecting the terminal fluorinated regulator shows 4-fluoro substituent with a polar effect could promote dipole-dipole interaction, 2,6-difluoro substituent with a twist effect could facilitate steric molecular configuration, while 3,5-difluoro substituent with twist & polar effects could regulate not only molecular configuration and π-π interaction but also dipole-dipole interaction. From the independent and joint effects of the three regulating positions, it is concluded that intermolecular interactions (i.e., dipole-dipole interaction, π-π interaction and perfluoroarene-arene interaction) and molecular configuration can be effectively fine-tuned by the degree and pattern of fluorination. In addition, their thermal stabilities are evaluated systematically. These results will provide a further insight into LC molecule design.

Electron-hole asymmetry in electrical conductivity of low-fluorinated graphene: numerical study

By using the real-space Green-Kubo formalism we study numerically the electron transport properties of low-fluorinated graphene. At low temperatures the diffuse transport regime is expected to be prevalent, and we found a pronounced electron-hole asymmetry in electrical conductivity as a result of quasi-resonant scattering on the localized states. For the finite temperatures in the variable-range hopping transport regime the interpretation of numerical results leads to the appearance of local minima and maxima of the resistance near the energies of the localized states. A comparison with the experimental measurements of the resistance in graphene samples with various fluorination degrees is discussed.

The Influence of Varying Fluorination Patterns on the Thermodynamics and Kinetics of Benzenesulfonamide Binding to Human Carbonic Anhydrase II

The fluorination of lead-like compounds is a common tool in medicinal chemistry to alter molecular properties in various ways and with different goals. We herein present a detailed study of the binding of fluorinated benzenesulfonamides to human Carbonic Anhydrase II by complementing macromolecular X-ray crystallographic observations with thermodynamic and kinetic data collected with the novel method of kinITC. Our findings comprise so far unknown alternative binding modes in the crystalline state for some of the investigated compounds as well as complex thermodynamic and kinetic structure-activity relationships. They suggest that fluorination of the benzenesulfonamide core is especially advantageous in one position with respect to the kinetic signatures of binding and that a higher degree of fluorination does not necessarily provide for a higher affinity or more favorable kinetic binding profiles. Lastly, we propose a relationship between the kinetics of binding and ligand acidity based on a small set of compounds with similar substitution patterns.

An innovative and eco-friendly modality for synthesis of highly fluorinated graphene by an acidic ionic liquid: Making of an efficacious vehicle for anti-cancer drug delivery

Fluorination of graphene nanomaterials has multitude merits owing to the peculiar temperament of the carbon-fluorine (C-F) bond. However, the current synthesis modalities of fluorinated graphene (FG) are based on the usage of toxic materials at high temperatures, which are problematic to be used. The methods to overcome these problems are challenging for chemists. Ionic liquids (ILs) have been used in several chemical processes as auxiliaries and eco-friendly alternatives instead of volatile organic solvents because of their properties. Consequently, herein we exploited a highly effective and green process for the synthesis of FG at mild temperature (80 °C) by using ammonium fluoride salt as fluorine agent and a synthesized acidic IL ([TEA]+[TFA]–) as a solvent. Our goal was to synthesize enriched FG with a high degree of fluorination (66.4 wt.% of F) and F/C ratio (2.2), which measured and confirmed by XPS analysis. Subsequently, the obtained FG was used as a nanocarrier for delivery of curcumin to cancerous cells. The in-vitro results showed that these nanosheets possessed a higher Cur-loading efficiency (78.43%) than commercial FG (52.12%) due to the sheet-like structure with folded edges. This, in turn, translated into an excellent in-vitro anti-cancer effect when tested against cancerous cells.

Flexibility of Fluorinated Graphene-Based Materials.

The resistivity of different films and structures containing fluorinated graphene (FG) flakes and chemical vapor deposition (CVD)-grown graphene of various fluorination degrees under tensile and compressive strains due to bending deformations was studied. Graphene and multilayer graphene films grown by means of the chemical vapor deposition (CVD) method were transferred onto the flexible substrate by laminating and were subjected to fluorination. They demonstrated a weak fluorination degree (F/C lower 20%). Compressive strains led to a strong (one-two orders of magnitude) decrease in the resistivity in both cases, which was most likely connected with the formation of additional conductive paths through fluorinated graphene. Tensile strain up to 3% caused by the bending of both types of CVD-grown FG led to a constant value of the resistivity or to an irreversible increase in the resistivity under repeated strain cycles. FG films created from the suspension of the fluorinated graphene with a fluorination degree of 20–25%, after the exclusion of design details of the used structures, demonstrated a stable resistivity at least up to 2–3% of tensile and compressive strain. The scale of resistance changes ΔR/R0 was found to be in the range of 14–28% with a different sign at the 10% tensile strain (bending radius 1 mm). In the case of the structures with the FG thin film printed on polyvinyl alcohol, a stable bipolar resistive switching was observed up to 6.5% of the tensile strain (bending radius was 2 mm). A further increase in strain (6.5–8%) leads to a decrease in ON/OFF current ratio from 5 down to 2 orders of magnitude. The current ratio decrease is connected with an increase under the tensile strain in distances between conductive agents (graphene islands and traps at the interface with polyvinyl alcohol) and thickness of fluorinated barriers within the active layer. The excellent performance of the crossbar memristor structures under tensile strain shows that the FG films and structures created from suspension are especially promising for flexible electronics.

Effect of crystallinity on thermal atomic layer etching of hafnium oxide, zirconium oxide, and hafnium zirconium oxide

Thermal atomic layer etching (ALE) can be achieved using sequential, self-limiting fluorination and ligand-exchange reactions. Previous studies have demonstrated thermal ALE of amorphous HfO2 and ZrO2 ALD films. This study explored the differences between thermal ALE of amorphous and polycrystalline films of hafnium oxide, zirconium oxide, and hafnium zirconium oxide on silicon wafers. HF, XeF2, or SF4 were used as the fluorination reactants. Titanium tetrachloride or dimethylaluminum chloride (DMAC) was employed as the metal precursor for ligand exchange. The spectroscopic ellipsometric measurements revealed that the amorphous films had much higher etch rates per cycle than the crystalline films regardless of the fluorination reactants or metal precursors for ligand exchange. The differences were most pronounced for HfO2. Using HF and TiCl4 as the reactants at 250 °C, the etch rates were 0.36 Å/cycle for amorphous HfO2 and 0.02 Å/cycle for crystalline HfO2. In comparison, the etch rates were 0.61 Å/cycle for amorphous ZrO2 and 0.26 Å/cycle for crystalline ZrO2. The etch rates were 0.35 Å/cycle for amorphous HfZrO4 and 0.04 Å/cycle for crystalline HfZrO4. When HF and DMAC were used as the reactants, the etch rates were higher than with HF and TiCl4 for every material. Using HF and DMAC as the reactants at 250 °C, the etch rates were 0.68 Å/cycle for amorphous HfO2 and 0.08 Å/cycle for crystalline HfO2. In comparison, the etch rates were 1.11 Å/cycle for amorphous ZrO2 and 0.82 Å/cycle for crystalline ZrO2. The etch rates were 0.69 Å/cycle for amorphous HfZrO4 and 0.16 Å/cycle for crystalline HfZrO4. SF4 as the fluorination reactant resulted in higher etch rates than for HF when using TiCl4 as the metal precursor for ligand exchange. XeF2 as the fluorination reactant resulted in even higher etch rates than for SF4. The differences in the etch rate with the fluorination reactant can be partially attributed to differences in thermochemistry for fluorination by HF, SF4, and XeF2. The differences in etch rates between amorphous and crystalline films may be caused by the greater degree of fluorination and subsequent ligand-exchange reaction for the amorphous films. The amorphous films have a lower density and may be able to better accommodate the large volume expansion upon fluorination.

NMR, magnetic and electronic investigations of fluorinated nanotubes with different coverage of fluorine

Effect of fluorination on the electronic and magnetic properties of the (9,0) Single Walled Carbon Nanotubes (SWCNTs) of two different patterns - single and double sided and 14%, 25% and 50% degrees of fluorination has been investigated theoretically. Enhanced ferro-magnetic behavior upon the increase in degree of fluorination is evident from the density of states. The band structure calculations reveal the metallic to semi- conducting transition with the increasing degrees of fluorination.The 19F NMR Chemical Shift Anisotropy (CSA) is best able to identify the different patterns and degrees of fluorination in SWCNTs.

Effects of cold SF6 plasma treatment on a-C:H, polypropylene and polystyrene

The effects of cold SF6 plasma treatment on amorphous hydrogenated carbon (FA), polypropylene (PP) and polystyrene (PS) were investigated as functions of gas pressure and applied power. An anticipated increase in hydrophobicity was confirmed by the greater water contact angles, θ, observed after all the treatments. Under the best conditions θ was increased by 50.8°, 57.2° and 21°, respectively. A rise and fall in θ was observed as the pressure of SF6 was increased, this trend being most consistent for FA. Although the plasma treatments caused some changes in surface roughness, measured using profilometry, there were no clear correlations between this parameter and θ. As revealed by Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS), the treated surfaces were fluorinated. As the degree of fluorination under optimal conditions was 2.2 at.%, 10.4 at.% and 36.3 at.% for the FA, PP and PS, respectively, this factor was not alone responsible for the observed increases in θ. Sulfur was attached to the surface of all the treated samples. The relative surface carbon content was reduced by the treatments. The main causes of the changes in θ upon treatment were the induced compositional and structural changes. Ageing for ten days caused a typical decrease in θ of ~10°, probably caused by rotation of hydrophobic surface groups into the surface.

Synthesis and Structural Diversity of Triaryl(phenylethyl)silanes

Starting from trichloro(phenylethyl)silane, six differently fluorinated triaryl(phenylethyl)silanes were synthesized by salt elimination reactions and their structures were determined by X-ray diffraction analysis. Tris(pentafluorophenyl)(phenylethyl)silane reveals a folded structure due to intramolecular π-stacking interactions, while those with a lower degree of fluorination show either intermolecular π-stacking or no interplay between the aryl groups. A similar folded structure was observed for (4-methylphenethyl)tris(pentafluorophenyl)silane and [2-(naphth-2-yl)ethyl]tris(pentafluorophenyl)silane, both generated from the corresponding trichlorosilanes. In contrast, the inversely fluorinated [2-(pentafluorophenyl)ethyl]triphenylsilane only revealed intermolecular π-stacking interactions. Compounds with tetrafluoropyridyl substituents behave differently; with these compounds, π-stacking is only observed between the fluorinated units. All compounds were analyzed by NMR and IR spectroscopy, elemental analyses and single-crystal X-ray diffraction, and found to have strong H/C/N/F···F and N···C contacts.