Bulky Trifluoromethyl Groups Research Articles

Preparation and Characterization of Semi-alicyclic Polyimides Containing Trifluoromethyl Groups for Optoelectronic Application.

Transparent polyimides (PI) films with outstanding overall performance are attractive for next generation optoelectronic and microelectronic applications. Semi-alicyclic PIs derived from alicyclic dianhydrides and aromatic diamines have proved effective to prepare transparent PIs with high transmittance. To optimize the combined properties of semi-alicyclic PIs, incorporating bulky trifluoromethyl groups into the backbones is regarded as a powerful tool. However, the lack of fundamental understanding of structure–property relationships of fluorinated semi-alicyclic PIs constrains the design and engineering of advanced films for such challenging applications. Herein, a series of semi-alicyclic PIs derived from alicyclic dianhydrides and trifluoromethyl-containing aromatic diamines was synthesized by solution polycondensation at high temperature. The effects of alicyclic structures and bulky trifluoromethyl groups on thermal, dielectric and optical properties of PIs were investigated systematically. These PI films had excellent solubility, low water absorption and good mechanical property. They showed high heat resistance with Tg in the range of 294–390 °C. It is noted that tensile strength and thermal stability were greatly affected by the rigid linkages and alicyclic moieties, respectively. These films exhibited obviously low refractive indices and significantly reduced dielectric constants from 2.61 to 2.76, together with low optical birefringence and dielectric anisotropy. Highly transparent films exhibited cutoff wavelength even as low as 298 nm and transmittance at 500 nm over 85%, displaying almost colorless appearance with yellowness index (b*) below 4.2. The remarkable optical improvement should be mainly ascribed to both weak electron-accepting alicyclic units and bulky electron-withdrawing trifluoromethyl or sulfone groups. The present work provides an effective strategy to design molecular structures of optically transparent PIs for a trade-off between solution-processability, low water uptake, good toughness, high heat resistance, low dielectric constant and excellent optical transparency.

Theoretical study of the binding profile of an allosteric modulator NS-1738 with a chimera structure of the α7 nicotinic acetylcholine receptor.

Potentiation of the function of the α7 nicotinic acetylcholine receptor (α7-nAChR) is believed to provide a possible way for the treatment of cholinergic system dysfunctions such as Alzheimer's disease and schizophrenia. Positive allosteric modulators (PAMs) are able to augment the peak current response of the endogenous agonist of α7-nAChR by binding to some allosteric sites. In this study, the binding profile of a potent type I PAM, NS-1738, with a chimera structure (termed α7-AChBP) constructed from the extracellular domain of α7-nAChR and an acetylcholine binding protein was investigated with molecular docking, molecular dynamics simulation, and free energy calculation methods. We found that NS-1738 could bind to three allosteric sites of α7-AChBP, namely, the top pocket, the vestibule pocket and the agonist sub-pocket. NS-1738 has moderate binding affinities (-6.76 to -9.15 kcal mol-1) at each allosteric site. The urea group is critical for binding and can form hydrogen-bond interactions with the protein. The bulky trifluoromethyl group also has a great impact on the binding modes and binding affinities. We believe that our study provides valuable insight into the binding profiles of type I PAMs with α7-nAChR and is helpful for the development of novel PAMs.

Rigid‐Rod Polyamides from 3,3′‐bis­(trifluoromethyl)‐4,4′‐diamino‐1,1′‐biphenyl

A diamine monomer with trifluoromethyl groups, 3,3′‐bis(trifluoromethyl)‐4,4′‐diamino‐1,1′‐biphenyl, is synthesized from 5‐bromo‐2‐nitrobenzotrifluoride with two steps. The model reaction with monofunctional benzoyl chloride at room temperature gives the model compound with a quantitative yield. The results of the model reaction indicate that the amine groups have sufficient reactivity in spite of the presence of electron‐withdrawing and bulky trifluoromethyl group at the ortho position. The monomer is polymerized with terephthaloyl chloride and isophthaloyl chloride in N,N‐dimethylacetamide (DMAc) or DMAc containing LiCl using pyridine as an acid acceptor at room temperature. All synthesized polymers are somewhat crystalline and colorless. While the meta‐linked polyamide (PA2) shows excellent solubility in polar aprotic solvents, the para‐linked one (PA1) is dissolved in polar aprotic solvents containing LiCl and concentrated H2SO4. They show good thermal and thermooxidative stability as well as high melting temperatures. image

Synthesis of a new trifluoromethylketone analogue of l-arginine and contrasting inhibitory activity against human arginase I and histone deacetylase 8

As part of our continuing search for new amino acid inhibitors of metalloenzymes, we now report the synthesis and biological evaluation of the trifluoromethylketone analogue of L-arginine, (S)-2-amino-8,8,8-trifluoro-7-oxo-octanoic acid (10). While this novel amino acid was initially designed as a potential inhibitor of human arginase I, it exhibits no measurable inhibitory activity against this enzyme. Surprisingly, however, 10 is a potent inhibitor of human histone deacetylase 8, with IC(50)=1.5 ± 0.2 μM. Additionally, 10 weakly inhibits the related bacterial enzyme, acetylpolyamine amidohydrolase, with IC(50)=110 ± 30 μM. The lack of inhibitory activity against human arginase I may result from unfavorable interactions of the bulky trifluoromethyl group of 10 in the constricted active site. Since the active site of histone deacetylase 8 is less constricted, we hypothesize that it accommodates 10 as the gem-diol, which mimics the tetrahedral intermediate and its flanking transition states in catalysis. Therefore, we suggest that 10 represents a new lead in the design of an amino acid or peptide-based inhibitor of histone deacetylases with simpler structure than previously studied trifluoromethylketones.

Synthesis, optical and electrochemical properties of novel hole-blocking poly(biphenylene-1,3,4-oxadiazole) containing electron-withdrawing trifluoromethyl groups

New poly(biphenylene-1,3,4-oxadiazole) P1 and poly(biphenylene hydrazide) P2 containing electron-withdrawing trifluoromethyl group at the 2 and 2′ positions of biphenyl moiety were synthesized. The biphenyl is forced to adapt a non-coplanar conformation due to the bulky trifluoromethyl group. High quality polymer P1 thin film can be easily obtained by thermal cyclodehydration from its soluble polyhydrazide precursor P2. The polymer P1 exhibited good thermal stability with glass transition temperature of 234 °C and 5% decomposition temperature of 469 °C. The optical and electrochemical properties were investigated by UV–vis spectroscopy, photoluminescence spectroscopy and cyclic voltammetry. For polymer P1 film, two absorption peaks at 370 and 414 nm were observed. It also exhibited a photoluminescent peak at 555 nm when excited by 414 nm light. The cyclic voltammetric studies revealed that polymer P1 had extremely low HOMO (−6.85 eV) and LUMO (−3.71 eV) energy levels due to the presence of strong electron-withdrawing trifluoromethyl group. It also exhibited a large energy gap (3.14 eV) which is an indication of short conjugation length resulted from non-coplanar biphenyl structure. Its HOMO energy was even lower than that of widely used hole-blocking material, 2-(4-biphenyl)-5-(4- tert-butylphenyl)-1,3,4-oxadiazole PBD (−6.30 eV). The low LUMO energy of polymer P1 could allow the easier electron injection from air-stable cathode such as aluminum. The good electron transfer ability was also shown by measuring the current density of electron-only devices with the structures of Al/ P1 (150 nm)/Alq 3 (50 nm)/Al and Al/Alq 3 (200 nm)/Al. Combined with high thermal stability and amorphous morphology, polymer P1 would be a promising candidate as the hole-blocking material for organic light-emitting diodes.

4′-[2-(Trifluoromethyl)phenyl]-2,2′:6′,2′′-terpyridine

The title compound, C22H14F3N3, is a versatile tridentate N-donor ligand consisting of a terpyridyl (terpy) molecule substituted in the 4′-position by a phenyl group, itself substituted in an ortho-position by a bulky trifluoro­methyl group. The phenyl ring is twisted as a result of steric inter­actions involving the bulky trifluoro­methyl substituent. This is reflected in the dihedral angle between the mean plane through the C atoms of the phenyl ring and the terpyridyl unit being 69.2 (1)°. The crystal structure contains no short van der Waals contacts. However, the terpy units stack in a head-to-tail orientation perpendicular to the c axis. The structure is is loosely stabilized by π–π inter­actions between the terminal pyridine rings of adjacent mol­ecules along the stack. The perpendicular distance between the mean planes through the terpy moieties of adjacent mol­ecules is 3.4 (1) Å.

Synthesis of new fluorine containing ring-opened polynorbornene dicarboximides using ruthenium alkylidene catalysts

The synthesis of new N-4-trifluoromethylphenyl-exo-endo-norbornene-5,6-dicarboximide (TFmNDI, 2a) and N-3,5-difluorophenyl-exo-endo-norbornene-5,6-dicarboximide (DFNDI, 2b) was carried out. Polynorbornene dicarboximides, 3a and 3b, were obtained via ring opening metathesis polymerization (ROMP) using bis(tricyclohexylphosphine) benzylidene ruthenium(IV) dichloride (I) and tricyclohexylphosphine [1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidene] ruthenium dichloride (II), respectively. Tg’s for polymers 3a and 3b were observed at 155 C and 142 C, respectively. Compared to polymer 3b, polymer 3a with the bulky trifluoromethyl group showed the highest glass transition temperature and improved mechanical properties.

(5,10,15,20-Tetraphenylporphyrinato-κ4 N)(2,2,2-trifluoro-1-phenylethylidene-κC 1)ruthenium(II): a stable fluorinated alkylidene complex of a ruthenium(II) porphyrin

In the title compound, [Ru(C44H28N4)(C8H5F3)], the fluorin­ated alkyl­idene group is bound to a five-coordinate Ru atom, which is located toward the carbene C atom, 0.3301 (5)Å from the least-squares plane of the C20N4 porphyrin core. The Ru=C bond is tilted slightly from the normal to the C20N4 least-squares plane due to steric repulsion between the porphyrinate ligand and the bulky trifluoro­methyl group. The Ru=C bond length of 1.838 (2) Å is comparable with those in bis­(subsituted phen­yl)carbene analogs.

Gas permeability of fluorinated hyperbranched polyimide

AbstractThe gas permeability of carbon dioxide, oxygen and nitrogen for hyperbranched polyimide (HBPI) containing trifluoromethyl groups were investigated. The HBPIs were prepared by condensation polymerization of a triamine monomer, 1,3,5‐tris(2‐trifluoromethyl‐4‐aminophenoxy) benzene (TFAPOB) and a commercially available dianhydride monomer 1,4‐bis(3,4‐dicarboxyphenoxy) benzene dianhydride (HQDPA). With different monomer addition methods and different monomer molar ratios, amine terminated HBPI (AM‐HQDPA) and anhydride terminated HBPI (AD‐HQDPA) were obtained, subsequently, the trifluoromethylphenyl amine terminated HBPI (CF3‐HQDPA) was achieved by modifying the end groups of AD‐HQDPA with (3,5‐ditrifluoromethyl)aniline. The CF3‐HQDPA exhibited a good mechanical and thermal stability as well as AM‐HQDPA, and showed better gas permeabilities than that of AM‐HQDPA because of increase of free volume contributed by the bulky trifluoromethyl group introduced, but, the selectivity ofCF3‐HQDPA was lower than that of AM‐HQDPA. This result was consistent with the trade‐off relationship. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Steric Effect of 3,5-Bis(trifluoromethyl)phenol as Hydrogen-Bond Donor on Outer-Sphere Complexation in the Synergistic Extraction of Aluminium(III) and Gallium(III) with 2,4-Pentanedione

Abstract The synergistic extraction of aluminium(III) and gallium(III) with 2,4-pentanedione (Hacac) in heptane from a weakly acidic solution was investigated in the presence of 3,5-bis(trifluoromethyl)phenol (BTMP). A large enhancement of the extraction of metal(III) was ascribed to the formation of outer-sphere complexes between metal(III) chelates and BTMP in the organic phase. Furthermore, an IR study demonstrated that the outer-sphere complexes were formed by the hydrogen bond between the hydroxy hydrogen atom of BTMP and the oxygen atoms of metal(III) chelates. The formation constants of the outer-sphere complexes with BTMP were determined and compared with those with 3,5-dichlorophenol (DCP) to understand the steric effect of the phenol derivative in this synergistic extraction. The bulky trifluoromethyl-group of BTMP and the short oxygen–oxygen nonbonded distance of Al(acac)3 resulted in a steric repulsion between two BTMP molecules to prevent the formation of Al(acac)3·3BTMP, although Al(acac)3·3DCP, Ga(acac)3·3BTMP, and Ga(acac)3·3DCP could be formed. Such a steric effect on outer-sphere complexation improves the separation efficiency between aluminium(III) and gallium(III) in the present synergistic extraction.

Optical and electroluminescent properties of novel poly(aryl ether)s with isolated carbazole and p‐quaterphenyl fluorophores

AbstractWe report the optical and electroluminescent properties of four novel poly(aryl ether)s (P1–P4) consisting of alternate isolated hole‐transporting [carbazole or 3,6‐bis(styryl)carbazole] and electron‐transporting [dicyano‐p‐quaterphenyl or bis(trifluoromethyl)‐p‐quaterphenyl] fluorophores. The photoluminescence (PL) spectra of the four polymeric films show maximum peaks around 407–413 nm for P1, P2 and 442–447 nm for P3, P4. The PL spectra of P1∼P4 are dependent on the composition of the two isolated fluorophores. According to the observation of relative quantum yield in poor solvent (cyclohexane), P2 containing more bulky trifluoromethyl groups in p‐quaterphenyl segments prevented aggregate quenching processes more than P1. Compared with P1 and P2 with carbazole segments, P3 and P4 with 3,6‐bis(styryl)carbazole segments exhibited less interchain interaction and a low threshold electric field in a single‐layer device. The p‐quaterphenyl and carbazole [or 3,6‐bis(styryl)carbazole] segments were regarded as electron‐transporting and hole‐transporting units, respectively, in the single‐layer light‐emitting diodes (Al/P1–P4/ITO). In the double‐layer device (ITO/MEH‐PPV/P2/Al), the maximum luminance was doubled, and the threshold electric fields diminished because P2 functioned as an electron‐transporting and hole‐blocking layer. Furthermore, the voltage‐tunable multicolor emission from orange to green was observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 333–340, 2004

Reactions of 2,3-epoxypolyfluoroalkanes with triethylamine

The reactions of 2,3-epoxyperfluoro- and 2,3-epoxy-ω-hydropolyfluoroalkanes with excess triethylamine at elevated temperatures yield secondary alcohols, which are the reduction products of intermediate isomeric ketones. Ring-opening occurs preferentially from the side of the less bulky trifluoromethyl group in all compounds except 2,3-epoxy-6-hydroundecafluorohexane.

Zur Chemie der l,3,5-Triaza-2-phosphinan-4,6-dione. Teil VI. Darstellung von 1,3,5-Triaza-2 λ3-, 1,3,5-Triaza-2 λ4- und 1,3,5-Triaza-2 λ5-phosphinan-4,6-dionen / Chemistry of the 1,3,5-Triaza-2-phosphinane-4,6-diones. Part VI. Synthesis of 1,3,5-Triaza-2λ3-, 1,3,5-Triaza-2λ4- and 1,3,5-Triaza-2λ5-phosphinane-4,6-diones

The reactions of 1,3,5-trimethylbiuret with dicyclohexylaminodichlorophosphine and with pyrrolidinodichlorophosphine furnished the triazaphosphinane-diones 1 and 2. Oxidation reactions of the 2-diorganoam ino-1,3,5-triorgano-1,3,5-triaza-2 λ3-phosphinane-4,6-diones 1, 2, and 4-9, as well as 2-fluoro-1,3,5-trimethyl-1,3,5-triaza-2λ3-phosphinane-4,6-dione 10 with hydrogen peroxide, elemental sulphur, phenyl azide, 1-adamantyl azide,p-nitrobenzoyl azide, tetrachloro-orthobenzoquinone, tetrabromo-orthobenzoquinone, 3,5-di-t-butyl-orthobenzoquinone, and hexafluoroacetone led to the respective oxidation products, 12-32, involving either λ4P or λ5P. In the reaction o f the P(III)C1 derivative 11 with 3-m ethyl-l,5-diphenyl-l,5- bis(trimethylsilyl)biuret the bifunctional compound 33 was produced. The new com pounds 1,2 and 12-33 were characterized via their 1H, 13C and 31P and, where appropriate, 19F NMR spectra. In the case o f the four compounds, 3 (previously described in the literature [2]), 13, 31, and 33, single crystal X-ray diffraction studies were conducted. Unusually for this type of heterocycle 3 displays a 1,4-diplanar ring conformation because o f the bulky aromatic substituents. 13 shows an envelope conformation. The hydrogen peroxide solvent molecule has crystallographic inversion symmetry, but may be disordered. In 31 the coordination geometry at phosphorus is trigonal bipyramidal. The five-membered ring shows a twist conform ation associated with the bulky trifluoromethyl groups. The exocyclic P-N bonds in 33 are unusually long.

Selective protonation of terminally bound η 3-allyls on (η 3-allyl) 2(μ 2-η 3-allyl) 2dimolybdenum(II) by β-diketones forming(μ 2-η 3a-allyl) 2(η 2-β-diketonate) 2 dimolybdenum(II) complexes

The β-diketones, R(CO)CH 2(CO)R′ [where R = R′= Me (acac); R = Me, R′= CF 3 (tfac); or R = R′ = CF 3 (hfac)] selectively protonate the terminally bound η 3-allyls on Mo 2(μ 2-η 3-allyl) 2(η 3-allyl) 2 ( A) leaving the Mo 2(μ 2-η 3-allyl) 2 core intact. The molybdenum(II) dimers, Mo 2(μ 2-η 3-allyl) 2(η 2-L) 2[where L = acac ( B), tfac ( C) or hfac ( D)] are formed from this reaction. From 1H, 13C and 19F NMR data, it is evident that the two bridging allyls in each complex, B- D, are bound in a cis arrangement with endo and exo conformations, respectively. Thus, a plane of symmetry bisects the MoMo bond axis and the two bridging allyls in B and D, but is absent parallel to the MoMo bond axis and bisecting each of the chelating β-diketonate ligands. The complex, C, exists primarily as the isomer in which the bulky trifluoromethyl groups on the two tfac ligands are as far apart as possible from each other. As the electron-donating ability of the terminally bound ligands in A- D decreases, allyl > acac > tfac > hfac, an upfield shift in the proton resonances of the bridging allyls is observed.