Fluorinated End Groups Research Articles

Ambient stable solution-processed organic field effect transistors from electron deficient planar aromatics: effect of end-groups on ambient stability.

Ambient stable solution processed n-channel organic field effect transistors (OFETs) are essential for next-generation low-cost organic electronic devices. Several molecular features, such as suitable orbital energy levels, easy synthetic steps, etc., must be considered while designing efficient active layer materials. Here, we report a case of improved ambient stability of solution-processed n-type OFETs upon suitable end-groups substitution of the active layer materials. A pair of core-substituted napthalenediimide (NDIFCN2 and EHNDICN2) derivatives with alkyl and perfluorinated end groups are considered. The transistor devices made out of these two derivatives exhibited largely different ambient stability behavior. The superior device stability (more than 25 days under ambient conditions) of one of the derivatives (NDIFCN2) was ascribed to the presence of fluorinated end groups that function as hydrophobic guard units inhibiting moisture infiltration into the active layer, thereby achieving ambient stability under humid conditions (>65% relative atmospheric humidity). Molecular level optical and electrochemical properties, thermal stability, and the solution-processed (spin coat and drop cast active layers) device characteristics are described in detail. Our findings highlight the requirement of hydrophobic end groups or sidechains for ambient stability of active layer materials, along with deep LUMO levels for ambient stability.

Synergetic Alkoxy Side‐Chain and Chlorine‐Contained End Group Strategy toward High Performance Ultra‐Narrow Bandgap Small Molecule Acceptors

Comprehensive SummaryUltra‐narrow bandgap (ultra‐NBG) small molecule acceptors (SMAs) show great potential in organic solar cells (OSCs) due to the extended near‐infrared (NIR) absorption. In this work, a synergetic alkoxy side‐chain and chlorine‐contained end group strategy is employed to achieve A‐DA'D‐A type ultra‐NBG SMAs by introducing alkoxy chains with oxygen atom at the second position into the thiophene β position as well as replacing the F atoms with Cl atoms in the end group. As a result, the heptacyclic BZO‐4F shows a redshifted absorption onset (960 nm) compared with Y11 (932 nm) without oxygen atoms in the side chains. Then, the fluorinated end groups are substituted with the chlorinated ones to synthesize BZO‐4Cl. The absorption onset of BZO‐4Cl is further redshifted to 990 nm, corresponding to an optical ultra‐NBG of 1.25 eV. When blending with the polymer donor PBDB‐T, the binary devices based on PBDB‐T:BZO‐4F and PBDB‐T:BZO‐4Cl deliver power conversion efficiencies (PCEs) over 12%. Furthermore, ternary devices with the addition of BZ4F‐O‐1 into PBDB‐T:BZO‐4Cl system achieve the optimal PCE of 15.51%. This work proposes a synergetic alkoxy side‐chain and chlorine‐contained end group strategy to achieve A‐DA'D‐A type ultra‐NBG SMAs, which is important for future molecular design.

2D Outer Side Chain‐Incorporated Y Acceptors for Highly Efficient Organic Solar Cells with Nonhalogenated Solvent and Annealing‐Free Process

To fabricate high‐performance organic solar cells (OSCs) by green solvent processing, it is essential to control the aggregation behavior and processability of constituent small‐molecule acceptors (SMAs). Herein, a series of SMAs (A1–A4) with enhanced aggregation behavior and processability is developed by replacing the linear alkyl outer side chains of BTP‐eC9 with 2D functional groups. The PM6:A1 SMA blend exhibits appropriate crystallinity, favorable blend morphology, superior electrical properties, and affords an OSC with a high power conversion efficiency (PCE) of 16.8%. Importantly, the OSC is fabricated using a nonhalogenated solvent (ortho‐xylene), annealing‐free process. In contrast, the reference PM6:BTP‐eC9‐based OSC exhibits a lower PCE of 15.3%. Structural analyses reveal that the 2D outer side chains of A1 induce steric hindrance between its dithienothiophen[3,2‐b]‐pyrrolobenzothiadiazole (BTP) core and the 2‐(3‐oxo‐2,3‐dihydroinden‐1‐ylidene)malononitrile end groups, optimizing its molecular planarity and aggregation property. It is further found that the SMAs with chlorinated IC end groups afford OSCs with higher PCEs than SMAs with fluorinated end groups.

Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains

Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains

M‐Series Nonfullerene Acceptors with Varied Fluorinated End Groups: Crystal Structure, Intermolecular Interaction, Charge Transport, and Photovoltaic Performance

Intermolecular interaction of nonfullerene acceptors (NFAs) is essential for controlling their photovoltaic performance. Fluorinated substituents attached at the end groups of NFAs can significantly affect their frontier molecular orbitals and intermolecular interactions. Herein, four heteroheptacene‐based NFAs (ML‐1F, ML‐2FO, ML‐2FM, and ML‐2FP) with different fluorinated end groups are designed, synthesized, and characterized. The impact of the end group on the crystal structures, optical, electrochemical, charge transport, and photovoltaic properties of these NFAs are systematically studied. In comparison with the acceptor with monofluorinated end groups, the acceptors with difluorinated end groups show reduced bandgaps and downshifted energy levels. Single‐crystal results demonstrate that the intermolecular interactions including the π–π stacking distance and molecular aggregation behavior of these acceptors are also affected by the variation of end groups thereby leading to the acceptors with varied charge transport properties. In combination with the polymer donor of PM6, ML‐2FM exhibits the highest power conversion efficiency (PCE) of 15.33% with a short‐circuit current density of 23.73 mA cm−2 and a fill factor of 0.734. However, ML‐2FP displays an inferior PCE of 10.48% which is lower than that of ML‐1F (11.41% PCE). The results show that the fluorine substituent number and position of end group are of vital importance in determining their photovoltaic performance.

Reduced miscibility between highly compatible non-fullerene acceptor and donor enables efficient ternary organic solar cells

The morphology of the photoactive layer within organic solar cells (OSCs) plays a key role in determining device performance. In addition to the film forming conditions, miscibility between donors and acceptors critically derives the corresponding morphology, which can be empirically evaluated by the Flory–Huggins interaction (χ). Herein, a new non-fullerene acceptor (NFA) with long alkyl chains and fluorinated end groups, BTP-4F–C9-20, is reported, which has sufficient solubility in common solvents and good miscibility with the polymer donor PM6. PM6:BTP-4F–C9-20 binary OSC achieved a maximum PCE of 16.5%, as a result of fine phase separation that creates abundant heterojunctions for exciton dissociation but insufficient bi-continuous pathways for charge transport. A chlorinated NFA Y7-BO with higher χ with PM6 is introduced into the PM6:BTP-4F–C9-20 host system, which increases phase separation with slightly enlarged domains to better shape the charge transport pathways. The PM6:BTP-4F–C9-20:Y7-BO (1:1.1:0.1) ternary OSC achieved a higher PCE of 17.3%, although Y7-BO provides limited complementary light absorption. This work demonstrates that the Flory–Huggins interaction is an effective parameter to fine tune the morphology of ternary OSCs to promote photovoltaic performance.

Effect of Building Block Connectivity and Ion Solvation on Electrochemical Stability and Ionic Conductivity in Novel Fluoroether Electrolytes.

Novel electrolytes are required for the commercialization of batteries with high energy densities such as lithium metal batteries. Recently, fluoroether solvents have become promising electrolyte candidates because they yield appreciable ionic conductivities, high oxidative stability, and enable high Coulombic efficiencies for lithium metal cycling. However, reported fluoroether electrolytes have similar molecular structures, and the influence of ion solvation in modifying electrolyte properties has not been elucidated. In this work, we synthesize a group of fluoroether compounds with reversed building block connectivity where ether moieties are sandwiched by fluorinated end groups. These compounds can support ionic conductivities as high as 1.3 mS/cm (30 °C, 1 M salt concentration). Remarkably, we report that the oxidative stability of these electrolytes increases with decreasing fluorine content, a phenomenon not observed in other fluoroethers. Using Raman and other spectroscopic techniques, we show that lithium ion solvation is controlled by fluoroether molecular structure, and the oxidative stability correlates with the “free solvent” fraction. Finally, we show that these electrolytes can be cycled repeatedly with lithium metal and other battery chemistries. Understanding the impact of building block connectivity and ionic solvation structure on electrochemical phenomena will facilitate the development of novel electrolytes for next-generation batteries.

Regio‐Regular Polymer Acceptors Enabled by Determined Fluorination on End Groups for All‐Polymer Solar Cells with 15.2 % Efficiency

AbstractPolymerization sites of small molecule acceptors (SMAs) play vital roles in determining device performance of all‐polymer solar cells (all‐PSCs). Different from our recent work about fluoro‐ and bromo‐ co‐modified end group of IC‐FBr (a mixture of IC‐FBr1 and IC‐FBr2), in this paper, we synthesized and purified two regiospecific fluoro‐ and bromo‐ substituted end groups (IC‐FBr‐o & IC‐FBr‐m), which were then employed to construct two regio‐regular polymer acceptors named PYF‐T‐o and PYF‐T‐m, respectively. In comparison with its isomeric counterparts named PYF‐T‐m with different conjugated coupling sites, PYF‐T‐o exhibits stronger and bathochromic absorption to achieve better photon harvesting. Meanwhile, PYF‐T‐o adopts more ordered inter‐chain packing and suitable phase separation after blending with the donor polymer PM6, which resulted in suppressed charge recombination and efficient charge transport. Strikingly, we observed a dramatic performance difference between the two isomeric polymer acceptors PYF‐T‐o and PYF‐T‐m. While devices based on PM6:PYF‐T‐o can yield power conversion efficiency (PCE) of 15.2 %, devices based on PM6:PYF‐T‐m only show poor efficiencies of 1.4 %. This work demonstrates the success of configuration‐unique fluorinated end groups in designing high‐performance regular polymer acceptors, which provides guidelines towards developing all‐PSCs with better efficiencies.

Regio-Regular Polymer Acceptors Enabled by Determined Fluorination on End Groups for All-Polymer Solar Cells with 15.2 % Efficiency.

Polymerization sites of small molecule acceptors (SMAs) play vital roles in determining device performance of all-polymer solar cells (all-PSCs). Different from our recent work about fluoro- and bromo- co-modified end group of IC-FBr (a mixture of IC-FBr1 and IC-FBr2), in this paper, we synthesized and purified two regiospecific fluoro- and bromo- substituted end groups (IC-FBr-o & IC-FBr-m), which were then employed to construct two regio-regular polymer acceptors named PYF-T-o and PYF-T-m, respectively. In comparison with its isomeric counterparts named PYF-T-m with different conjugated coupling sites, PYF-T-o exhibits stronger and bathochromic absorption to achieve better photon harvesting. Meanwhile, PYF-T-o adopts more ordered inter-chain packing and suitable phase separation after blending with the donor polymer PM6, which resulted in suppressed charge recombination and efficient charge transport. Strikingly, we observed a dramatic performance difference between the two isomeric polymer acceptors PYF-T-o and PYF-T-m. While devices based on PM6:PYF-T-o can yield power conversion efficiency (PCE) of 15.2 %, devices based on PM6:PYF-T-m only show poor efficiencies of 1.4 %. This work demonstrates the success of configuration-unique fluorinated end groups in designing high-performance regular polymer acceptors, which provides guidelines towards developing all-PSCs with better efficiencies.

Microbubbles decorated with dendronized magnetic nanoparticles for biomedical imaging: effective stabilization via fluorous interactions.

Dendrons fitted with three oligo(ethylene glycol) (OEG) chains, one of which contains a fluorinated or hydrogenated end group and bears a bisphosphonate polar head (CnX2n+1OEG8Den, X = F or H; n = 2 or 4), were synthesized and grafted on the surface of iron oxide nanoparticles (IONPs) for microbubble-mediated imaging and therapeutic purposes. The size and stability of the dendronized IONPs (IONP@CnX2n+1OEG8Den) in aqueous dispersions were monitored by dynamic light scattering. The investigation of the spontaneous adsorption of IONP@CnX2n+1OEG8Den at the interface between air or air saturated with perfluorohexane and an aqueous phase establishes that exposure to the fluorocarbon gas markedly increases the rate of adsorption of the dendronized IONPs to the gas/water interface and decreases the equilibrium interfacial tension. This suggests that fluorous interactions are at play between the supernatant fluorocarbon gas and the fluorinated end groups of the dendrons. Furthermore, small perfluorohexane-stabilized microbubbles (MBs) with a dipalmitoylphosphatidylcholine (DPPC) shell that incorporates IONP@CnX2n+1OEG8Den (DPPC/Fe molar ratio 28:1) were prepared and subsequently characterized using both optical microscopy and an acoustical method of size determination. The dendrons fitted with fluorinated end groups lead to smaller and more stable MBs than those fitted with hydrogenated groups. The most effective result is already obtained with C2F5, for which MBs of ≈1.0 μm in radius reach a half-life of ≈6.0 h. An atomic force microscopy investigation of spin-coated mixed films of DPPC/IONP@C2X5OEG8Den combinations (molar ratio 28:1) shows that the IONPs grafted with the fluorinated dendrons are located within the phospholipid film, while those grafted with the hydrocarbon dendrons are located at the surface of the phospholipid film.

Fluorinated heptacyclic carbazole-based ladder-type acceptors with aliphatic side chains for efficient fullerene-free organic solar cells

Side chain engineering (phenyl side chains to aliphatic side chains) and fluorinated end groups (IC to 2FIC) are utilized to construct high performance NFA with high planarity.

Controlling Open-Circuit Voltage in Organic Solar Cells by Terminal Fluoro-Functionalization of Narrow-Bandgap π-Conjugated Molecules

A series of narrow-bandgap π-conjugated small molecules composed of benzodithiophene (BDT) and diketopyrrolopyrrole (DPP) chromophoric units with different electron-withdrawing fluorinated end groups was designed and synthesized as donor materials for systematically studying their structure–property relationship in organic solar cells (OSCs). The terminal fluoro-functionalization of the π-conjugated BDT-DPP backbone resulted in systematic changes in the HOMO and LUMO energy levels of the resulting materials, as well as in their subsequent OSC device performance. These materials possessed relatively low HOMO energy levels ranging from −5.23 to −5.47 eV, while simultaneously maintaining small bandgap energies of approximately 1.6 eV in their thin films. With such proper engineering of the HOMO energy levels, the bulk heterojunction OSCs based on these fluoro-functionalized molecules as donor materials and PC71BM as an acceptor material demonstrated high open-circuit voltages of up to 0.94 V. In this series ...

Composite membranes with surface-modifying macromolecules for halogenated hydrocarbons removal from water in membrane extraction process

Flat sheet composite polysulfone (PSf) membranes blended with surface-modifying macromolecules (SMM) were prepared, characterized, and tested for halogenated hydrocarbons (HHC) (i.e. trichloroethylene, TCE) permeation and separation from water in an extractive membrane system. The fluorine end groups in SMMs facilitated its migration towards the membrane surface during membrane casting, whereas the polydimethylsiloxane component rendered the SMM organophilic which improved the surface affinity of the composite membrane towards TCE. Polydimethylsiloxane content in SMM, SMM content in PSf, and air-exposure of the casted blend solutions before membrane formation were found critical in obtaining an effective composite membrane. The presence of a selective SMM layer on the membrane surface was confirmed via contact angle measurement, Fourier-transform infrared spectrometry analysis, and field emission-scanning electron microscope. The most effective composite membrane (PSf with 15 wt% H-SMM and air exposed for 5 min before phase inversion) exhibited TCE flux values ranging between 640 and 1790 mg/m2 h when fed with TCE concentrations between 30 and 105 mg/L. Overall results demonstrate the potential use of the composite extractive membrane for the removal of hydrophobic organic contaminants like HHCs from aqueous streams.

Impact of fluorinated end groups on the properties of acceptor–donor–acceptor type oligothiophenes for solution-processed photovoltaic cells

Two new oligothiophene derivatives with the acceptor–donor–acceptor structure incorporating fluorinated alkyl cyanoacetate units as the terminal acceptor groups, DCAE7T-F1 and DCAO7T-F7, have been designed and synthesized for solution-processable BHJ solar cells. The impacts of these fluorinated end groups on the optical absorption, solubility, electrochemical properties, morphology, surface energy, film forming ability, mobility and solar cell performance were studied. We found that as the fluorinated alkyl length increased, the surface energy decreased and the lipophobicity increased. Due to its high lipophobic property and a problem with its wettability, DCAO7T-F7 was not able to produce a uniform film by spin coating. A power conversion efficiency (PCE) of 2.26% was achieved with an open-circuit voltage (Voc) of 0.83 V, short circuit current (Jsc) of 5.55 mA cm−2 and fill factor (FF) of 0.50 for DCAE7T-F1 based solar cells. The low Jsc suggests that controlling the film morphology and molecular assembly is essential for the performance of these fluorinated small molecules.

Synthesis of Perfluoroalkyl End-Functionalized Poly(3-hexylthiophene) and the Effect of Fluorinated End Groups on Solar Cell Performance

A series of well-defined perfluoroalkyl end-functionalized poly(3-hexylthiophenes) (P3HT) were synthesized by Stille coupling of stannylated 2-perfluoralkylthiophene with the bromine end of P3HT. The length of the perfluoroalkyl end group was varied from −C4F13 to −C8F17. These polymers were fully characterized and tested in bulk heterojunction solar cells with phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor. Performance of the solar cells was highest for the unmodified P3HT and decreased as the length of the perfluoroalkyl end increased. The most affected device parameters were the short-circuit current density (Jsc) and series resistance, pointing to lower charge carrier mobility and poor morphology as the cause for the lower performance. While the morphology of blends did not significantly change with perfluoroalkyl end modification, analysis of blended films by energy-filtered transmission electron microscopy (EF-TEM) revealed wider P3HT domains, consistent with the perfluorinated end groups segregating to the edge or exterior of P3HT domains, causing two domains to join. This study demonstrates that the perfluoroalkyl end group can be detrimental to polymer solar cell device performance, and further work toward understanding the interface between the donor and acceptor phases is required to fully understand this effect.

Well-Defined Star-Shaped Rod−Coil Diblock Copolymers as a New Class of Unimolecular Micelles: Encapsulation of Guests and Thermoresponsive Phase Transition

A series of star-shaped rod−coil diblock copolymers composed of poly(arylene ether sulfone) (PAES) as a core, and poly[2-(2-methoxyethoxy)ethyl methacrylate-co-oligo(ethylene glycol) methacrylate] [poly(MEO2MA-co-OEGMA)] as a shell was synthesized by combination of chain-growth condensation polymerization (CGCP) and atom transfer radical polymerization (ATRP). In the presence of 4-arm initiator (1), CGCP of 4-fluoro-4′-hydroxydiphenyl sulfone potassium salt (2) via nucleophilic aromatic substitution (SNAr) reaction yielded a well-defined star-shaped polymer with four fluorine end groups (C5−F and C8−F). Transformation of the fluorine groups into ATRP initiating sites produced a macroinitiator having four bromine groups (C5−Br and C8−Br). In the presence of the macroinitiator, random copolymerization of MEO2MA and OEGMA via ATRP formed thermoresponsive shell blocks to produce a desired star-shaped PAES-b-poly(MEO2MA-co-OEGMA) block copolymer with various block lengths. Dynamic light scattering (DLS) of the...

Fabrication of Aromatic‐Aliphatic Aminoketone Polymers with Terminal Fluorine Groups

AbstractA procedure for synthesis aromatic‐aliphatic PAK, completely functionalized withp‐fluorophenyl terminal groups, is presented. This synthesis uses the nucleophilic aromatic substitution of DFB with various secondary aliphatic diamines [CH3NH(CH2)mNHCH3] (m = 3, 6, and 8) and cesium fluoride as the base catalyst in the melt. The linearity and the complete functionalization of the PAK compounds withp‐fluorophenyl terminal groups are demonstrated with the aid of MALDI TOF mass spectrometry. PAK compounds are semi‐crystalline as shown by WAXS and DSC measurements. The degree of crystallinity ranges between 2 and 25%. Nucleophilic aromatic substitution reactions in the fluorine end groups are demonstrated by reaction of PAK (m = 6) with the strongS‐nucleophile mercaptoacetic acid.magnified image

Surface Depletion of the Fluorine Content of Electrospun Fibers of Fluorinated Polyurethane

For materials containing fluorine, it has been generally accepted that fluorinated segments or end groups tend to aggregate in the outer surface because of the low surface energy, which endows the fluorinated materials with special surface properties such as self-cleaning, superhydrophobicity, and so forth. However, for the electrospun fibrous membranes of polyurethane elastomers containing perfluoropolyether segments (FPU), abnormal fluorine aggregations in the core of the electrospun fibers were observed. The XPS analysis indicated a rather low fluorine content at the surface of the electrospun FPU fibers. Further study with dynamic light scattering and fluorescence showed that FPU chains can form aggregates in the concentrated solution. Therefore, it can be deduced that the rapid evaporation of solvent and fast formation of fibers during the electrospinning process could result in the freeze-in of the aggregated chain conformation and the depletion of fluorine units on the surface of the electrospun FPU fibers.

Order, disorder and stretching of a smectic elastomer with ‘side-on’ mesogenic side groups

We report an X-ray study of the order in a ‘side-on’ smectic-A elastomer in which both the polymer backbone and the mesogenic side groups are, on average, parallel to the smectic layer normal. The present system shows in all phases locally correlated structures as evidenced by systematic diffuse scattering at small angles, attributed to the fluorinated end groups of the mesogens. The elastomer shows order of the smectic layers over a limited range in spite of the relatively low crosslink concentration (4%). Upon stretching along the layer normal we find a linear increase of the smectic layer period for small loading (elastic regime). These changes parallel the stress variation for the elastic part of the macroscopic stress–strain curve and saturate at larger strains. The attendant increase in the width of the X-ray peaks indicates a decrease of the average domain dimensions. In the plastic regime no distortion of the smectic monodomain structure or layer rotation is observed. Instead the stress is relieved by ‘melting’ of the layer structure giving rise to a nematic-like state with short-range layer correlations: at the final stage about four smectic layers.

Synthesis and analytical follow-up of the mineralization of a new fluorosurfactant prototype

Fluorinated surfactants have become essential in numerous technical applications due to their unparalleled effectiveness and efficiency. The environmental persistence of the non-biodegradable perfluorinated alkyl moiety has become a matter of concern. Therefore, it was searched for new molecules with chemically stable fluorinated end groups which can be microbially transformed into labile fluorinated substances.One prototype substance, 10-(trifluoromethoxy)decane-1-sulfonate, has shown biomineralization. Monitoring the formation of metabolites over time elucidated the mechanism of biotransformation. Analysis was performed utilizing liquid chromatography–single quadrupole mass spectrometry (LC–MS) and quadrupole-time of flight tandem mass spectrometry (QqTOF-MS).It was possible to distinguish between two major degradation pathways of the fluorinated alkylsulfonate derivative: (i) a desulfonation and subsequent oxidation and degradation of the alkyl chain being predominant and (ii) an insertion of oxygen with a subsequent cleavage and degradation of the molecule. The utilized trifluoromethoxy-endgroup resulted in instable trifluoromethanol after degradation of the alkyl chain, which led to a high degree of mineralization of the molecule.