Effect Of Fluorine Substituents Research Articles

Investigating the Effects of Fluorine Substituents on Organic Dyes in Dye-Sensitized Solar Cells

We synthesized and evaluated five organic dyes that featured both mono- and di-substituted fluorine atoms for application in dye-sensitized solar cells (DSSCs). The dye structure was designed with N, N-dimethylaniline as a donor, fluorophenyl as an π-conjugated bridge, and cyanoacetic acid as an anchoring and acceptor group. The fluorine substituents are strong electron-withdrawing groups, introducing different numbers and positions of fluorine atoms (ortho and meta) that were expected to the ability of the acceptor parts of the dye. The results showed that adding the fluorine mono-substitution in the ortho position can enhance the efficiency of the solar cells in comparison with the meta-substitution and unsubstituted one. However, the di-substitution by fluorine atoms in two ortho positions and ortho, meta positions reduced the performance of the solar cells. The reason was related to the effect of π-conjugation between the fluorine substituent and the carbonyl group of the carboxylic acid. The DSSCs based on dye 14 achieved the best results with power conversion efficiency (PCE) = 3.33%, (Jsc = 5.43 mA cm-2, Voc = 0.81V and FF = 75.85%) under standard conditions with I3-/I- as the electrolyte.

Computational insights into the synergistic interplay of ligand and fluorine effects in palladium-catalyzed regiodivergent decarboxylative allylic alkylation

DFT calculations were performed to investigate palladium-catalyzed decarboxylative allylic alkylation of allyl difluoro-β-ketoesters. The synergistic effects of ligand and fluorine substituents on regioselectivity were uncovered.

Balance the trade-offs between high birefringence, large dielectric anisotropy and low viscosity in nematic liquid crystals through molecular splicing strategy

ABSTRACT A series of liquid crystals containing one n-propyl/n-propoxy, lateral fluorine substituent, a tolane mesophase unit, and a 2,2-difluorovinyl terminal group were designed and synthesised. Their chemical structures were characterised and confirmed by nuclear magnetic resonance (NMR), mass spectrometry and Fourier transform infrared spectrometry (FTIR) instruments. Meanwhile, the position and number effects of lateral fluorine substituents on the thermal, mesomorphic, and electro-optical properties of these compounds were explored. Furthermore, density functional theory (DFT) calculations of molecular conformation, polarisability components and dipole moment were utilised to correlate the experimental results. Research results show that the 2,2-difluorovinyl-terminated liquid crystal compounds possess excellent properties of low melting point, wide nematic-phase temperature interval, high birefringence, large dielectric anisotropy and low rotational viscosity. This molecular splicing strategy is an effective method to balance the trade-offs between high birefringence, large dielectric anisotropy, and low viscosity in nematic liquid crystals.

Iridium‐Catalysed C−H Borylation of Fluoroarenes: Insights into the Balance between Steric and Electronic Control of Regioselectivity

AbstractThe iridium catalysed C−H borylation of polyfluorinated arenes and heteroarenes occurs rapidly and efficiently. As with other borylation reactions, whilst steric parameters dominate, an underlying electronic influence on reaction selectivity can be observed. Notably borylation regioselectivity in fluorinated (hetero)arenes is determined by purely electronic effects except for ortho‐borylation between two fluorine atoms where steric effects of fluorine substituents become apparent. Borylation at the para position with respect to fluorine is disfavoured whereas a strong electronic preference for borylation para to the azinyl nitrogen of pyridine is observed. When these features co‐operate high selectivity can be expected. For these reactions, computations based on transition state, rather than intermediate, energies in iridium geometries showed excellent agreement between predicted and observed selectivities.

Potent and biostable inhibitors of the main protease of SARS-CoV-2

Potent and biostable inhibitors of the main protease (Mpro) of SARS-CoV-2 were designed and synthesized based on an active hit compound 5h (2). Our strategy was based not only on the introduction of fluorine atoms into the inhibitor molecule for an increase of binding affinity for the pocket of Mpro and cell membrane permeability but also on the replacement of the digestible amide bond by a surrogate structure to increase the biostability of the compounds. Compound 3 is highly potent and blocks SARS-CoV-2 infection invitro without a viral breakthrough. The derivatives, which contain a thioamide surrogate in the P2-P1 amide bond of these compounds (2 and 3), showed remarkably preferable pharmacokinetics in mice compared with the corresponding parent compounds. These data show that compounds 3 and its biostable derivative 4 are potential drugs for treating COVID-19 and that replacement of the digestible amide bond by its thioamide surrogate structure is an effective method.

Synthesis of fluoroalkenes via Julia and Julia-Kocienski olefination reactions

The introduction of one or two fluorine atoms into a carbon-carbon double bond often brings about profound changes of physical, chemical and/or biological properties of the target molecule. Fluorinated alkenes are a class of important compounds and widely used in medicinal chemistry and materials science. Julia and Julia-Kocienski reactions could be used in the synthesis of fluorinated alkenes by employing α-fluorinated sulfones. In this review, the synthesis of fluorinated alkenes through Julia and Julia-Kocienski reactions are summarized, and the contents are categorized by target molecules and sulfone reagents. The difference between the reaction conditions for monofluoromethyl sulfones and difluoromethyl sulfones reflects the unique effect of fluorine substituents.

Effect of fluorine substituents on photovoltaic properties of D–a type conjugated polymers with quinoxaline unit

Two quinoxaline-based polymers were synthesized to investigate the effect of electron-withdrawing fluorine substituents on the photovoltaic properties of the polymers. In order to prepare the reference quinoxaline-based D-A type polymer PBS-T-Q, the electron-donating benzodithiophene derivative and electron-accepting 2,3-dithenylquinoxaline moiety were polymerized under the Stille condition. Thereafter, the strong electron-withdrawing fluorine atom was incorporated into the 6-position of the 2,3-dithenylquinoxaline unit of the reference polymer to yield the additional target polymer PBS-T-QF. The photovoltaic properties of the two polymers were examined by manufacturing an inverted-type device the photovoltaic properties of the quinoxaline-based polymers were enhanced by the addition of a fluorine substituent.

The effect of fluorine substituents on the crystal structure and spin crossover behavior of the cation [MnIII(3,5-diHal-sal2323)]+ complex family with BPh4 anions

The effect of fluorine substituents on the structure and magnetic behavior of [Mn(R′,R′′-sal2323)]BPh4 complexes was studied and compared it with that of chlorine and bromine substituents.

Effect of electron-withdrawing fluorine and cyano substituents on photovoltaic properties of two-dimensional quinoxaline-based polymers

In this study, strong electron-withdrawing fluorine (F) and cyano (CN) substituents are selectively incorporated into the quinoxaline unit of two-dimensional (2D) D–A-type polymers to investigate their effects on the photovoltaic properties of the polymers. To construct the 2D polymeric structure, electron-donating benzodithiophene and methoxy-substituted triphenylamine are directly linked to the horizontal and vertical directions of the quinoxaline acceptor, respectively. After analyzing the structural, optical, and electrochemical properties of the resultant F- and CN-substituted polymers, labeled as PBCl-MTQF and PBCl-MTQCN, respectively, inverted-type polymer solar cells with a non-fullerene Y6 acceptor are fabricated to investigate the photovoltaic performances of the polymers. It is discovered that the maximum power conversion efficiency of PBCl-MTQF is 7.48%, whereas that of PBCl-MTQCN is limited to 3.52%. This significantly reduced PCE of the device based on PBCl-MTQCN is ascribed to the formation of irregular, large aggregates in the active layer, which can readily aggravate the charge recombination and charge transport kinetics of the device. Therefore, the photovoltaic performance of 2D quinoxaline-based D–A-type polymers is significantly affected by the type of electron-withdrawing substituent.

Fluorinated α-Diimine Nickel Mediated Ethylene (Co)Polymerization.

Fluorine substituents in transition metal catalysts are of great importance in olefin polymerization catalysis; however, the comprehensive effect of fluorine substituents is elusive in seminal late transition metal α-diimine catalytic system. In this contribution, fluorine substituents at various positions (ortho-, meta-, and para-F) and with different numbers (Fn ; n=0, 1, 2, 3, 5) were installed into the well-defined N-terphenyl amine and thus were studied for the first time in the nickel α-diimine promoted ethylene polymerization and copolymerization with polar monomers. The position of the fluorine substituent was particularly crucial in these polymerization reactions in terms of catalytic activity, polymer molecular weight, branching density, and incorporation of polar monomer, and thus a picture on the fluorine effect was given. As a notable result, the ortho-F substituted α-diimine nickel catalyst produced highly linear polyethylenes with an extremely high molecular weight (Mw =8703 kDa) and a significantly low degree of branching of 1.4/1000 C; however, the meta-F and/or para-F substituted α-diimine nickel catalysts generated highly branched (up to 80.2/1000 C) polyethylenes with significantly low molecular weights (Mw =20-50 kDa).

Fluorination vs. Chlorination: Effect on the Sensor Response of Tetrasubstituted Zinc Phthalocyanine Films to Ammonia

In this work, the effect of fluorine and chlorine substituents in tetrasubstituted zinc phthalocyanines, introduced into the non-peripheral (ZnPcR4-np, R = F, Cl) and peripheral (ZnPcR4-p, R = F, Cl) positions of macrocycle, on their structure and chemiresistive sensor response to low concentration of ammonia is studied. The structure and morphology of the zinc phthalocyanines films (ZnPcR4) were investigated by X-ray diffraction and atomic force microscopy methods. To understand different effects of chlorine and fluorine substituents, the strength and nature of the bonding of ammonia and ZnPcHal4 molecules were studied by quantum chemical simulation. It was shown on the basis of comparative analysis that the sensor response to ammonia was found to increase in the order ZnPcCl4-np < ZnPcF4-np < ZnPcF4-p < ZnPcCl4-p, which is in good agreement with the values of bonding energy between hydrogen atoms of NH3 and halogen substituents in the phthalocyanine rings. ZnPcCl4-p films demonstrate the maximal sensor response to ammonia with the calculated detection limit of 0.01 ppm; however, they are more sensitive to humidity than ZnPcF4-p films. It was shown that both ZnPcF4-p and ZnPcCl4-p and can be used for the selective detection of NH3 in the presence of carbon dioxide, dichloromethane, acetone, toluene, and ethanol.

Mechanistic Study of Potent Fluorinated EGFR Kinase Inhibitors with a Quinazoline Scaffold against L858R/T790M/C797S Resistance Mutation: Unveiling the Fluorine Substituent Cooperativity Effect on the Inhibitory Activity.

Fluorination has considerable potential with regard to the design of kinase inhibitors for anticarcinoma therapy. It was recently reported that fluorination increases the potency of inhibitors of the epidermal growth factor receptor (EGFR), mutations of which have been linked specifically to nonsmall-cell lung cancer. For the L858R/T790M/C797S triplet mutant (EGFRTM), a difluorinated inhibitor, 25g, was found to have 4.23 times greater potency against the EGFRTM than an unfluorinated inhibitor, 25a. This discovery necessitates a rational explanation for the underlying inhibitory mechanisms. Here, we apply multiple computational approaches to explore, validate, and differentiate the binding modes of 25a and 25g in the EGFRTM and investigate the cooperativity effect of fluorine substituents on the inhibitory activity. Our results showed that the EGFRTM in the presence of 25g undergoes a series of conformational changes that favor inhibitor binding to both the active and allosteric sites. Further, the cooperativity effect of fluorine substituents is positive: the complex stability is increased by each additional fluorine substituent. Estimated binding free energies show good correlation with the experimental biological activity. Subsequently, the decomposition energy analysis revealed that the van der Waals interaction is the principal force contributing to variations in the binding affinities of 25a and 25g to the EGFRTM. Per-residue energy-based hierarchical clustering analysis suggests that three hot-spot residues, L718, K745, and D855, are the key in achieving optimal binding modes for 25g with higher affinity in the EGFRTM compared to 25a. This study provides a rationale for the superior EGFRTM-inhibitory potency exhibited by 25g over 25a, which is expected to be useful for the future rational structure-based design of novel EGFRTM inhibitors with improved potency and selectivity.

Impact of Polymer Backbone Fluorination on the Charge Generation/Recombination Patterns and Vertical Phase Segregation in Bulk Heterojunction Organic Solar Cells.

Incorporating fluorine (–F) substituents along the main-chains of polymer donors and acceptors is an effective strategy toward efficient bulk-heterojunction (BHJ) solar cells. Specifically, F-substituted polymers often exhibit planar conformations, leading to favorable packing, and electronic coupling. However, the effects of fluorine substituents on the charge generation and recombination characteristics that determine the overall efficiency of BHJ active layers remain critically important issues to examine. In this report, two PBDT[2X]T polymer analogs –poly[4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4, 5-b′]dithiophene-thiophene] [PBDT[2H]T] and its F-substituted counterpart poly[4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene-3,4-difluoro-thiophene] [PBDT[2F]T]—are studied to systematically examine how –F substituents impact the blend morphology, charge generation, carrier recombination and extraction in BHJ solar cells. Considering the large efficiency differences between PBDT[2H]T- and PBDT[2F]T-based BHJ devices, significant emphasis is given to characterizing the out-of-plane morphology of the blend films as vertical phase-separation characteristics are known to have dramatic effects on charge transport and carrier extraction in polymer-fullerene BHJ solar cells. Herein, we use electron energy loss spectroscopy (EELS) in tandem with charge transport characterization to examine PBDT[2X]T-fullerene blend films. Our analyses show that PBDT[2H]T and PBDT[2F]T possess very different charge generation, recombination and extraction characteristics, resulting from distinct aggregation, and phase-distribution within the BHJ blend films.

Effect of fluorine substituents on benzothiadiazole-based D-π-A'-π-A photosensitizers for dye-sensitized solar cells.

Two D–π–A′–π–A organic dyes with triazatruxene (TAT) as the electron donor, thiophene as the π-spacer, benzoic acid as the anchor group, and benzothiadiazole (BT) or difluorobenzo[c][1,2,5]thiadiazole (DFBT) as the additional acceptor, namely LS101 and LS102, respectively, were applied to dye-sensitized solar cells (DSSCs). As fluorine substituents are usually strong electron-withdrawing groups, introducing two fluorine atoms into BT was expected to strengthen the electron-withdrawing ability of the auxiliary acceptor, resulting in DSSCs with a broader light capture region and further improved power conversion efficiency (PCE). Fluorine is the smallest electron-withdrawing group with an induction effect, but can also act as an electron-donating group owing to its conjugation effect. When the conjugation effect is dominant, the electron-withdrawing ability of additional acceptor DFBT decreases instead. Accordingly, the band gap of LS102 was broadened and the UV-vis absorption spectrum was blue-shifted. In the end, DSSCs based on LS101 achieved a champion PCE of 10.2% (Jsc = 15.1 mA cm−2, Voc = 966 mV, FF = 70.1%) while that based on LS102 gave a PCE of only 8.6% (Jsc = 13.4 mA cm−2, Voc = 934 mV, FF = 69.1%) under standard AM 1.5G solar irradiation (100 mW cm−2) with Co2+/Co3+ as the electrolyte.

Effects of fluorine and phenyl substituents on oxygen sensitivity and photostability of cyclometalated platinum(II) complexes

Fluorinated cyclometalated Pt(II) complexes Pt(Fppy)(acac) and Pt(dFppy)(acac), phenyl-substituted LA1, and 2,4-difluorophenyl-substituted LA2 were synthesized and applied as phosphorescent probes for monitoring of molecular oxygen compared with a model complex Pt(ppy)(acac). The phosphorescence of all Pt(II) complexes in tetrahydrofuran (THF) or immobilized in ethyl cellulose (EC) films was gradually quenched with the increase of the oxygen concentration. The intensity ratio I0/I9.61 and I0/I100 were used to evaluate oxygen sensitivities of the Pt(II) complexes in THF and in EC film, respectively. LA1 demonstrates the highest oxygen sensitivity with I0/I9.61 of 19.5 in THF, and I0/I100 of 13.5 and a KSVapp of 16.9 bar–1 in EC film. The photostability tests of the Pt(II) complexes immobilized EC films show that, phenyl and fluorine substituents have a synergistic effect on improving the photostability of the complexes. The LA2-immobilized EC film demonstrates the highest photostability and excellent operational stability (3.8 s on going from 100% N2 to 100% O2 and 4.5 s on going from 100% O2 to 100% N2), which is a potential photostable probe for online monitoring of molecular oxygen.

Rhodium‐Catalyzed Defluorinative Vinylation of gem‐Difluoroalkenes for the Synthesis of 2‐Fluoro‐1,3‐dienes

Summary of main observation and conclusionHerein, we present a strategy for the formation of 2‐fluoro‐1,3‐diene derivatives via rhodium‐catalyzed direct C(sp2)—C(sp2) cross‐coupling of gem‐difluoroalkenes and acrylamides. By merging Rh(III)‐catalyzed C(sp2)–H bond activation and nucleophilic addition/F‐elimination of gem‐difluoroalkene, an efficient defluorinative vinylation reaction is uncovered, which leads to the generation of 2‐fluoro‐1,3‐dienes in moderate to good yields with excellent stereoselectivity under mild conditions. Preliminary mechanistic study suggests unique effects of fluorine substituents which allow the reactivity profile not observed with the congeners bearing heavier halides.

Fluorine‐Substituted Ligands Induce Structural Diversity of Coordination Compounds

AbstractSeven inorganic coordination compounds based on HgBr2 and Ln−F ligands, in which Ln−F are N‐(fluorinated phenyl)‐2‐pyrazinecarboxamide, bearing fluorine substituent in different position on phenyl ring have been synthesized. These complexes, [HgBr2(L2−F)2]n, 1, [HgBr2L3−F]n, 2, [HgBr2L4−F]n, 3, [HgBr2L2,5−F]n, 4, [HgBr2(L2,6−F)2], 5, [HgBr2L2,3,4−F], 6, and [HgBr2L2,3,4,5−F]n, 7, are characterized in order to get precise insight into the fluorine substituent effect on the coordination structures. The crystal structure data resulting from X‐ray diffraction reveal that, in spite of the same metal, counter ion and reaction conditions, overall structural diversity is evident in all cases. Accordingly, fluorinated ligand exercise influence on not only first coordination sphere but also supramolecular architecture and overall construction. As a matter of fact, small changes in the position and number of fluorine existed on the phenyl ring direct both first and second coordination sphere around metal ion.

Time dependent – density functional theory characterization of organic dyes for dye-sensitized solar cells

We aim at providing better insight into the parameters that govern the intramolecular charge transfer (ICT) and photo-injection processes in dyes for dye-sensitised solar cells (DSSC). Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations are utilized to study the geometry, electronic structure, electrostatic potential (ESP) and absorption spectrum, for a representative donor-π bridge-acceptor (D–π–A) dye for DSSC. The coplanar geometry of the dye (D1) facilitates strong conjugation and considerable delocalization originating the π CT interaction from donor to acceptor orbitals and the hyper-conjugative interactions involving Rydberg states. A model simulating the adsorption of the dye on the TiO2 surface is utilized to estimate binding energies. The effect of fluorine substituents in the π-spacer on the quantum efficiency of DSSCs was investigated. Gibb’s free energy values, redox potentials, excited state lifetime, non-linear optical properties (NLO) and driving forces for D1 and its fluorinated derivatives were computed.

Effect of substitution on the optoelectronic properties of dyes for DSSC. A DFT approach

The present work aims at a better and deeper insight into the forces that govern the intramolecular charge transfer (ICT) and photo injection processes in dyes for dye sensitized solar cells (DSSC). The geometry, electronic structure, electron density distribution, and absorption spectra, for a selected donor-[Formula: see text]-acceptor (D-[Formula: see text]-A) dye for DSSC were computed and analyzed at a high level of DFT theory. The coplanar geometry of the studied dye (D1) indicates a strong conjugation which facilitates ICT. NBO analyses reveal that this ICT amounts to 0.8e, which is localized on the acceptor and anchoring groups resulting in a marked total delocalization interaction energy. The origin of this stabilization is two-fold; first the [Formula: see text]-charge transfer (CT) interaction from donor to acceptor orbitals and the hyperconjugative interactions involving Rydberg states. The effect of fluorine substituents, in the [Formula: see text]-spacer, on the quantum efficiency of DSSCs was investigated. Gibb’s free energy values, redox potentials, excited state life time, non-linear optical properties (NLO) and driving forces for D1 and its fluorinated derivatives were computed.

Experimental and theoretical insight into the effect of fluorine substituents on the properties of azine linked covalent organic frameworks

Herein we report a combined experimental and computational study on the effect of fluorine atom incorporation on the materials properties of azine-linked COFs.