Fluorophobic Effect Research Articles

Betaketothioesters in organocatalysis: Harnessing nucleophilic reactivity, the fluorophobic effect, and expanding the substrate repertoire

The use of thioesters as nucleophiles marks a considerable change in organic synthesis. This new method, propelled by gentle enolization with minimal catalyst loading, results in enantiomeric excesses surpassing 95 % under ambient conditions, accomplishing total conversion in merely 6 h. Remarkably, this method eliminates the need for additional functional groups in nitroalkenes for efficient chirality transfer from the organocatalyst. The exceptional reactivity of thioesters, combined with their water tolerance, enables reactions utilizing the hydrophobic effect, resulting in reaction times as short as 15 min and products with slightly enhanced stereoselectivity compared to analogous reactions in dichloromethane. Additionally, reactions performed in perfluorinated solvents outpace their homogenous counterparts in organic solvents, delivering products in shorter time with comparable stereoselectivity. This work highlights the rare utilization of the fluorous effect in organocatalysis. Simple squaramides also exhibit remarkable catalytic activity in the reactions of beta-keto thioesters with alpha-bromo nitroalkenes. As little as 0.1 mol% of the catalyst leads to product formation with an 86 % yield (qNMR) and 93 % enantiomeric excess. Upscaling the reaction does not significantly affect the enantiomeric excess but leads to a slight decrease in yield from 82 % to 77 %. It has been demonstrated that thioesters react more rapidly than their ketoester counterparts, and the two-step reaction leading to dihydrofuran ring closure is entirely accomplished by extending the reaction time, eliminating the need for additional base. The examples presented here expand the range of substrates derived from carboxylic acid esters in catalytic reactions, suggesting the potential for the synthesis of challenging reactions in analogs of alkoxyl esters. Additional KS-DFT calculations shed more light on the reaction paths, rationalizing the observed stereochemical outcomes.

Enhancing the binding of calix[5]arene containers for ferrocenes by a fluorophobic effect through the release of high-energy perfluoro-1-iodoalkanes

The release of high-energy perfluoro-1-iodohexane molecules has been demonstrated as a major driving force for enhanced binding between calix[5]arene containers and ferrocene guests.

Porous helical supramolecular columns self-organized via the fluorophobic effect of a semifluorinated tapered dendron.

The self-organizable dendron (4-3,4-3,5)12G2X with X = -CO2CH3 and -CH2OH, an already classic dendron, facilitating the formation of a large diversity of columnar hexagonal phases including crystalline, with intracolumnar order, and liquid crystalline, and providing access for the first time to mimics of the transmembrane protein water channel Aquaporin was semifluorinated at eight of the sp3 hybridized carbons of its alkyl groups to provide (4-3,4-3,5)4F8G2X. The self-organization of (4-3,4-3,5)4F8G2X was analyzed by a combination of oriented fiber intermediate angle X-ray scattering, wide angle X-ray scattering, electron density maps, and reconstructed X-ray diffractograms by emplying molecular models. These experiments demonstrated that fluorophobic effect of (4-3,4-3,5)4F8G2X mediated mostly via the helical confiormation of the fluorinated fragments sharper miocrosegregation of the fluorinated fragments in the most ordered states of the resulting 124 helical porous columns. These results support the original model of self-organization of dendrons and provide access to new and simpler synthetic avenues for the construction of mimics of aquaporin channels which are of great interest for cell biology and for the next generation of membranes for water separation and water purification.

Mesomorphic properties of cyanobiphenyl dimers with a substituted central malonate unit: overruling effect of fluorination

ABSTRACT Two series of C2-substituted dimers carrying a central C2-hexyl- or C2-nonafluorohexyl malonate and two cyanobiphenyls attached via alkoxy spacers of various lengths (n = 6–12) were synthesised, and the mesomorphic properties were studied by differential scanning calorimetry, polarising optical microscopyand X-ray diffraction (wide-angle and small-angle X-ray scattering). The C2-substituent dimers together with the spacer lengths had a pronounced influence on the phase behaviour. In case of C2-hexyl-substituted dimers, shorter spacers favoured N phases (n = 6–9), while longer spacers favoured SmA phases (n ≥ 9). In addition, decreased clearing temperatures were observed. In contrast, C2-nonafluorohexyl-substituted dimers suppressed N phases and displayed only SmA phases. Moreover, clearing temperatures and phase stabilities considerably increased. Based on the experimentally determined layer thickness, a packing model for the SmA phases was proposed, where C2-substituted dimers displaced mesophases with molecules in a Y-conformation. As a result, less stable mesophases for C2-hexyl-substituted dimers due to weakened intermolecular interactions and more stable mesophases for C2-nonafluorohexyl-substituted dimers due to the fluorophobic effect and nanosegregation were obtained.

Increasing the Fluorine Substituent of Thieno[3,4-c]pyrrole-4,6-dione Terthiophene Copolymers Progressively Narrows the Nanofibrils and Enhances the Efficiency of Fullerene-Based Polymer Photovoltaics

Five thieno­[3,4-c]­pyrrole-4,6-dione (TPD)-terthiophene copolymers, PHT, P1F3HT, P1F1HT, P3F1HT, and PFT, having 0, 25, 50, 75, and 100% of fluorine substituents on the center of terthiophene exhibit a progressive increase of open-circuit voltage (VOC), short-circuit current density (JSC), and hence a power conversion efficiency (PCE) up to 9.68% of PC61BM-blended copolymer photovoltaics, which is the highest PCE reported for TPD-based polymer solar cells with fullerene derivatives as the electron acceptor. It is evident in atomic force microscopy and transmission electron microscopy studies that the width of copolymer nanofibrils formed in solar cells decreases progressively with the increasing fluorine substituents of the copolymers. A declining solubility, which is attributed to the fluorophobic effect, narrows the nanofibril of copolymers with more fluorine substituents. Grazing incidence wide angle X-ray scattering studies reveal the improved crystallinity of lamellar stacking and π–π stacking structures of copolymers with more fluorine substituents. Density functional theory calculation indicates a virtually coplanar conformation of terthiophene units with fluorine substituents. The increasing VOC is also associated with the increasing fluorine substituents, which lower the highest occupied molecular orbital energy level of the copolymers verified by the electrochemical and photoelectron spectroscopic measurements.

Tunable Fluorophobic Effect Determines Nanoparticle Dispersion in Homopolymers and Block Polymers

AbstractThe controlled placement of nanoparticles (NPs) within homopolymers and block polymers is of broad interest for functional nanomaterials. This manuscript focuses on small molecule‐stabilized NPs that bring a large fraction of functionality. For such NP mixtures with block polymers, the overwhelming focus to date has been the use of attractive interactions to localize hydrophilic NPs within the hydrophilic portion of block polymers. Related lipophilic approaches often place NPs at the block polymer interface. Here, a new modality for block polymer–NP control is developed that rather relies upon repulsion via the fluorophobic effect. Fluorinated species strongly associate via repulsion from nonfluorinated media. Here, fluorinated NPs are made with ligand mixtures for granular control over the strength of the fluorophobic effect. Small‐angle X‐ray scattering data reveal that all F‐NPs readily phase separate from polystyrene whereas increasing fluorophobic strength enables dispersions within a fluorinated homopolymer. Next, the F‐NP placement within diblock polymers is investigated as a function of the fluorophobic strength. Weakly fluorophobic F‐NPs are found predominantly near the diblock interface whereas strongly fluorophobic F‐NPs are found to disperse throughout the fluorinated block. The controlled placement of NPs is an emerging way to self‐assemble materials.

Fluorophobic Effect Promoting Lamellar Self-Assembly of Donor Acceptor Dyes.

To combine liquid crystalline and linear optical properties in the same molecule, the fluorophobic effect was probed for the first time in donor acceptor dyes. Thus, a series of mono-, bi-, and tricyclic donor acceptor dyes with 1H,1H-perfluorinated alkyl chains of different lengths as donor units and nitrile, malononitrile or barbiturate as acceptor units was synthesized in 5 steps and 1.4-6.6 % overall yield. UV/Vis and fluorescence spectroscopy, cyclic voltammetry and DFT calculations revealed that absorption and emission maxima, Stokes shifts and LUMO energies were mainly governed by the chromophore size and acceptor strengths. The perfluorinated chain was electronically almost decoupled from the remaining chromophore and induced only slight changes of the absorption maxima as compared to the alkyl substituted counterparts. However, in contrast to the non-mesomorphic alkyl donor-substituted derivatives, the perfluorinated donors resulted in self-assembly into partially interdigitated SmA bilayers according to differential scanning calorimetry (DSC), polarizing optical microscopy (POM), X-ray diffraction (WAXS, SAXS) studies and electron density profile calculations.

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

Herein, we demonstrate that a bottom-up approach, based on halogen bonding (XB), can be successfully applied for the design of a new type of ionic liquid crystals (ILCs). Taking advantages of the high specificity of XB for haloperfluorocarbons and the ability of anions to act as XB-acceptors, we obtained supramolecular complexes based on 1-alkyl-3-methylimidazolium iodides and iodoperfluorocarbons, overcoming the well-known immiscibility between hydrocarbons (HCs) and perfluorocarbons (PFCs). The high directionality of the XB combined with the fluorophobic effect, allowed us to obtain enantiotropic liquid crystals where a rigid, non-aromatic, XB supramolecular anion acts as mesogenic core. X-ray structure analysis of the complex between 1-ethyl-3-methylimidazolium iodide and iodoperfluorooctane showed the presence of a layered structure, which is a manifestation of the well-known tendency to segregation of perfluoroalkyl chains. This is consistent with the observation of smectic mesophases. Moreover, all the reported complexes melt below 100 °C, and most are mesomorphic even at room temperature, despite that the starting materials were non-mesomorphic in nature. The supramolecular strategy reported here provides new design principles for mesogen design allowing a totally new class of functional materials.

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding.

Herein, we demonstrate that a bottom-up approach, based on halogen bonding (XB), can be successfully applied for the design of a new type of ionic liquid crystals (ILCs). Taking advantages of the high specificity of XB for haloperfluorocarbons and the ability of anions to act as XB-acceptors, we obtained supramolecular complexes based on 1-alkyl-3-methylimidazolium iodides and iodoperfluorocarbons, overcoming the well-known immiscibility between hydrocarbons (HCs) and perfluorocarbons (PFCs). The high directionality of the XB combined with the fluorophobic effect, allowed us to obtain enantiotropic liquid crystals where a rigid, non-aromatic, XB supramolecular anion acts as mesogenic core.X-ray structure analysis of the complex between 1-ethyl-3-methylimidazolium iodide and iodoperfluorooctane showed the presence of a layered structure, which is a manifestation of the well-known tendency to segregation of perfluoroalkyl chains. This is consistent with the observation of smectic mesophases. Moreover, all the reported complexes melt below 100 °C, and most are mesomorphic even at room temperature, despite that the starting materials were non-mesomorphic in nature.The supramolecular strategy reported here provides new design principles for mesogen design allowing a totally new class of functional materials.

Fluorophobic Effect Driven Self‐Organization of Semifluorinated Alkyl Chain Substituted Conjugated Polymer

This paper reports on the effect of a semifluorinated alkyl side chain for achieving a self‐organized nanostructure to facilitate the efficient charge carrier transport. So far, semifluorinated alkyl side chains have rarely been introduced into semiconducting polymers, despite their interesting properties such as hydrophobicity, thermal stability, and solvent resistance, as well as self‐organization. Herein, this study synthesizes the semifluorinated alkyl chain introduced poly(3‐dodecylthiophene), SFA‐P3DT, and demonstrates that self‐organization of SFA‐P3DT is intensely induced in nonfluorous solvent by the so‐called fluorophobic effect, resulting in the formation of nanofibrillar structure. In presence of the semifluorinated alkyl side chain, organic thin film transistor (OTFT) devices exhibit the improved charge carrier mobility than that of poly(3‐dodecylthiophene) with hydrocarbon alkyl chain. Moreover, higher charge carrier mobility can be obtained from the nonfluorous solvent, in comparison to the fluorous solvent, confirming the crucial role of fluorophobic effect. These observations suggest that the introduction of semifluorinated alkyl chains into a conjugated polymer may enhance the performance of OTFTs through the development of a well‐ordered nanostructure via self‐organization by fluorophobic effect, which, in turn, facilitates the efficient charge carrier transport. image

Switchable dielectric permittivity with temperature and Dc-bias in a semifluorinated azobenzene derivative

The thermodynamic, optical, structural, and dynamic properties of the semifluorinated (E)-1-(4-octylphenyl)-2-(4-(perfluorooctyl)phenyl)diazene (4) and the corresponding (E)-1,2-bis(4-octylphenyl)diazene (5) have been studied with differential scanning calorimetry, polarizing optical microscopy, X-ray diffraction, and dielectric spectroscopy. 4 combines the azobenzene properties with the fluorophobic effect and gives rise to a responsive material with a temperature and dc-bias-driven switchable dielectric permittivity within the narrower nematic phase. This is caused by the nematic potential that inevitably brings some fluorocarbon chains in proximity to the hydrocarbon chains from adjacent molecules. Frustration is alleviated by reducing the nematic-to-isotropic transition temperature and by increasing the crystalline-to-nematic transition temperature, thus limiting the stability of the nematic phase. Unlike the normal isotropic phase of compound 5, the isotropic phase of compound 4 contains dipoles with short-range orientation correlations. Optimizing the type of interactions may result in materials with applications as molecular switches and electrooptic devices.

A Novel Thermally Reversible Soluble‐Insoluble Conjugated Polymer with Semi‐Fluorinated Alkyl Chains: Enhanced Transistor Performance by Fluorophobic Self‐Organization and Orthogonal Hydrophobic Patterning

SFA-PQT exhibits self-assembly via a fluorophobic effect in a non-fluorous solvent, which leads to an enhanced electrical performance. Ambipolar transistors and inverters with p- and n- type bilayersare enabled by the unique thermally reversible soluble-insoluble properties of SFA-PQT. More importantly, the hydrophobicity of SFA-PQT facilitates orthogonal hydrophobic patterning and a patterned inverter exhibits low voltage dissipation, a narrow transition zone, a high gain value, and negligible hysteresis.

Synthesis and simultaneous self‐assembly of multiblock fluorinated polyurethane in iniferter polymerization

AbstractA multiblock fluorinated polyurethane was synthesized using tetraphenylethane‐based polyurethane as macroiniferter to free‐radically polymerize 1H,1H,3H‐trihydro perfluoro‐2,4‐dimethylpentyl methacrylate (FDPMA). Simultaneous self‐assembly occurred in FDPMA polymerization process and various nanostructures, like multicore particles, formed depending on FDPMA concentration. Fluorophobic effect and the cooperation of the fluorinated blocks with polyurethane blocks are demonstrated to be the main contribution. That soluble FDPMA in DMF becomes insoluble after polymerization triggers the self‐assembly process and leads to the nanostructure formation, and the polyurethane blocks that are soluble in DMF and immiscible with the fluorinated blocks stabilize the discrete nanostructures. Further, the nanostructures in solutions can evolve into various morphologies, such as disk and fiber, when dried to solid state. All these results not only reveal the feasibility and robustness of the multiblock copolymer on the modulation of self‐assembly structure but also represent a facile and efficient approach for novel nanostructure construction. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013

CH/π-Interaction-Guided Self-Assembly in π-Conjugated Oligomers

We report CH/π hydrogen-bond-driven self-assembly in π-conjugated skeletons based on oligophenylenevinylenes (OPVs) and trace the origin of interactions at the molecular level by using single-crystal structures. OPVs were designed with appropriate pendants in the aromatic core and varied by hydrocarbon or fluorocarbon tails along the molecular axis. The roles of aromatic π-stack, van der Waals forces, fluorophobic effect and CH/π interactions were investigated on the theromotropic liquid crystallinity of OPV molecules. Single-crystal structures of hydrocarbon OPVs provided direct evidence for the existence of CH/π interactions between the π-ring (H-bond acceptor) and alkyl C-H (H-bond donor). The four important crystallographic parameters, d(c-x)=3.79 Å, θ=21.49°, φ=150.25° and d(Hp-x)=0.73 Å, matched in accordance with typical CH/π interactions. The CH/π interactions facilitate the close-packing of mesogens in x-y planes, which were further protruded along the c axis producing a lamellar structure. In the absence of CH/π interactions, van der Waals interactions drove the assembly towards a Schlieren nematic texture. Fluorocarbon OPVs exhibited smectic liquid-crystalline textures that further underwent Smectic A (SmA) to Smectic C (SmC) phase transitions with shrinkage up to 11%. The orientation and translational ordering of mesogens in the liquid-crystalline (LC) phases induced H- and J-type molecular arrangements in fluorocarbon and hydrocarbon OPVs, respectively. Upon photoexcitation, the H- and J-type molecular arrangements were found to emit a blue or yellowish/green colour. Time-resolved fluorescence decay measurements confirmed longer lifetimes for H-type smectic OPVs relative to that of loosely packed one-dimensional nematic hydrocarbon-tailed OPVs.

Synthesis, characterization and surface wettability of polythiophene derivatives containing semi-fluorinated liquid-crystalline segment

In the scope of increasing our knowledge on the elaboration of smart surfaces, the aim of this work was to synthesize monomers as starting materials for the polymerization or copolymerization via electrochemical route. We report the synthesis and characterization of original structures containing a single phenyl unit bound, on one side, to a semi-fluorinated tail via a thioester connector and, on the other side, to a thiophene moiety. This design approach using cheap raw materials (a single phenyl ring as mesogenic core) associated to an electropolymerizable unit is of great interest in the development of liquid crystal low cost materials to build-up non-wetting surfaces based on the fluorophobic effect. The mesomorphic properties were characterized using differential scanning calorimetry and optical polarizing microscopy. The effect of the length of the fluorinated tail induced the formation of a smectic enantiotropic mesophase for F-hexyl and F-octyl tails. The polymerization of the films was performed in solution of sodium perchlorate in acetonitrile. Hydrophobic surfaces were obtained from the monomers containing a F-hexyl and F-octyl tail, while superhydrophobic surfaces (contact angle of water of 158°) were reached from the monomer containing a F-butyl tail.

Effect of terminal perfluorocarbon chain containing mesogens on phase behaviors of chiral comb-like liquid crystalline polymers

A novel perfluorinated liquid crystal 4′-(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctanoyloxy)biphenyl-4-yl undec-10-enoate (PFOBU) was synthesized, which exhibited smectic C phase. Several liquid crystalline polymers (PI–PVI) were synthesized by use of poly(methylhydrogeno)siloxane, PFOBU, and cholesteryl 3-(4-allyloxy-phenyl)-acryloate. The chemical structures and liquid crystalline (LC) properties of the monomers and polymers, and some ferroelectric properties of the chiral smectic C (SC*) phase were characterized by use of various experimental techniques. The effect of perfluorocarbon chains on phase behaviors of the fluorinated LC polysiloxanes was studied as well. PI and PII showed single chiral nematic (N*) mesophase when they were heated and cooled, but PIII, PIV, PV, and PVI containing more perfluorocarbon chain units exhibited SC* phase besides N* mesophase. Introduction of perfluorocarbon chain containing mesogens to the chiral cholesteryl-containing polymer systems resulted in a SC* mesophases, indicating that the fluorophobic effect could lead to microphase segregation and modifications of smectic mesophases from the chiral nematic phase.

In situ vacuum measurement of the thickness dependence of electron mobility in naphthalenetetracarboxylic diimide-based field-effect transistors

We present an in situ electrical measurement for the characteristics of n-channel organic field-effect transistors (OFETs) based on N,N′-dipentadecafluorooctyl-1,4,5,8-naphtalene tetracarboxylic diimide (NTCDI-C8F15) organic semiconductors. The field-effect mobilities have been estimated as a function of the number of monolayers (MLs). The electron mobility (μe) of NTCDI-C8F15 OFET as thin as 2 ML has been determined. μe increases rapidly with increasing film thickness, although it reaches saturation thickness (d0) around 3.5 ML. Atomic force microscopy confirms island mode growth mechanism of NTCDI-C8F15 with near upright position stacking on SiO2 substrate and it is attributed to the fluorophobic effect of the material.

Synthesis and characterization of fluorine‐containing liquid crystalline polysiloxanes bearing cholesteryl cinnamate mesogens and trifluoromethyl‐substituted mesogens

AbstractSeveral novel side‐chain liquid crystalline (LC) polysiloxanes bearing cholesteryl cinnamate mesogens and trifluoromethyl‐substituted mesogens were synthesized by a one‐step hydrosilylation reaction with poly(methylhydrogeno)siloxane, a cholesteric LC monomer cholesteryl 3‐(4‐allyloxy‐phenyl)‐acryloate and a fluoro‐containing LC monomer 4‐[2‐(3‐trifluoromethyl‐phenoxy)‐acetoxy]‐phenyl 4‐allyloxy‐benzoate. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques, such as FTIR, 1H‐NMR, 13C‐NMR, TGA, DSC, POM, and XRD. The temperatures at which 5% weight loss occurred were greater than 300°C for all the polymers, and the residue weight near 600°C increased slightly with increase of the trifluoromethyl‐substituted mesogens in the fluorinated polymer systems. The samples containing mainly cholesteryl cinnamate mesogens showed chiral nematic phase when they were heated and cooled, but the samples containing more trifluoromethyl‐substituted mesogens exhibited chiral smectic A mesophase. The glass transition temperature of the series of polymers increased slightly with increase of trifluoromethyl‐substituted mesogens in the polymer systems, but mesophase–isotropic phase transition temperature did not change greatly. In XRD curves, the intensity of sharp reflections at low angle increased with increase of trifluoromethyl‐substituted mesogens in the fluorinated polymers systems, indicating that the smectic order derived from trifluoromethyl‐substituted mesogens should be strengthened. These results should be due to the fluorophobic effect between trifluoromethyl‐substituted mesogens and the polymer matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Nanoscale segregation, molecular recognition and fluorophobic effect – from molecular design towards complex mesophase morphologies

Mesomorphic structure formation of hydrogen-bonded complexes of amino substituted 1,3,5-triazines with complementary (semiperfluoro)alkoxybenzoic acids is presented. The substitution pattern of both components was modified systematically in order to elucidate the influence of molecular parameters on the mesophase morphologies of the binary mixed systems. The phase sequence of the triazines, and of their associates with the acids, spans the range from smectic layer structures to discontinuous cubic phases composed of closed inverted micelles. Columnar phases with various two-dimensional lattice symmetries and bicontinuous cubic phases were found as intermediates. The mesophase morphologies are discussed in terms of the microsegregation of rigid polar, lipophilic and fluorinated molecular blocks in different sub-spaces along with tailoring the shape of (curved) aggregates by the space requirement of incompatible molecular fragments.

Synthesis of unsymmetric triphenylene discotic liquid crystals with a semi-fluorinated chain and the influence of fluorophobic effect on mesogenic behavior

The fluorophobic effect of the semi-fluorinated chain of discotic molecules efficiently improves the stability of columnar mesophase. Low symmetric discogens exhibit decreased melting points and wide mesophase ranges. A series of triphenylene derivatives 1, C18H6(OCnH2n+1)4(OMe)(O2CC2H4C6F13), and their hydrocarbon analogues 2, C18H6(OCnH2n+1)4(OMe)(O2CC8H17), n = 4−8, were synthesized for the investigation of the influence of semi-fluorinated peripheral chain and molecular symmetry on mesomorphism. The structures were characterized with 1H NMR and MS. The mesomorphism was studied with differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The results showed that all triphenylene derivatives exhibited enantiotropic columnar mesophase. The semifluorinated triphenylenes 1a–1e displayed higher melting points and clearing points than their hydrocarbon analogies 2a–2e. Most of them were in columnar mesophase at room temperature.