Perfluorophenyl–Phenyl Interactions in the Crystallization and Topochemical Polymerization of Triacetylene Monomers

A series of symmetrically and unsymmetrically substituted octa‐2,4,6‐triyne‐1,8‐diol derivatives with benzoyl, 4‐dodecyloxybenzoyl, as well as perfluorobenzoyl substituents were prepared and investigated with respect to their crystal structures and topochemical polymerizability. Single‐crystal structures for several of these triacetylene monomers have been obtained and proved that the perfluorophenyl–phenyl interactions played a decisive role in the molecular packing. As a consequence of the geometric requirements imposed by the perfluorophenyl–phenyl interactions, packing parameters appropriate for a topochemical triacetylene polymerization in the sense of either a 1,6‐ or a 1,4‐polyaddition along different crystallographic axes were observed in two cases, and UV irradiation led to successful polymerization. Raman as well as solid‐state ¹³C NMR spectra of the obtained polymers revealed that the polymerization had predominantly proceeded in the form of a 1,4‐polyaddition.     

Synthesis and solid-state structure of perfluorophenyl end-capped polyynes

Five new supramolecular building blocks have been synthesized on the basis of polyynes end-capped with pentafluorophenyl groups, including three symmetrical (16, 17, 18) and two unsymmetrical polyynes (7 and 12). The solid-state behavior of these molecules based on the attractive electrostatic interactions of the phenyl and perfluorophenyl groups has been examined by X-ray crystallographic analysis of 7, 12, and 16.25.     

Spectroscopy on photografted polyethylene surfaces using a perfluorophenyl azide: Evidence for covalent attachment

The present study was conducted in order to confirm C―H insertion of a perfluorophenyl nitrene, produced by UV‐irradiation of a perfluorophenyl azide, to polyethylene surfaces. It was shown previously that water‐repelling, oil‐repelling, and dirt‐repelling polyethylene surfaces can be created by “grafting to” of perfluoroalkanes using a photoreactive surface modifier based on azide/nitrene chemistry. The abrasion resistance of the new surfaces was enhanced compared with a coating using a simple, long‐chain perfluoroalkane. However, covalent binding of the surface modifier was not unequivocally demonstrated. Here, spectroscopic information is presented suggesting that, indeed, a monomolecular, covalently bound grafted layer is formed from the photodecomposition of a perfluorophenyl azide on polyethylene surfaces. Infrared spectroscopy showed that the peak from the azide moiety disappeared upon UV‐irradiation, and the light dose for completion of the photo decomposition was determined to be approximately 322 mJ/cm². A model compound mimicking the grafted nitrene species was synthesized, having a λ_max of 281 nm in hexane. The photografted and washed layer had a λ_max of 286 nm, indicating a good conformity with the model compound. X‐ray photoelectron spectroscopy of the nitrogen species from the photografted layer showed a peak at 400.0 eV. The model compound had a N 1s binding energy of 399.7 eV, thus being comparable.     

Miscibility of methacrylic polymers with different pendant groups

Miscibility is not always common in blends of homologous polymers that differ in structure but possess the same functional groups. In this study, two methacrylate polymers, which differ by a methylene unit, were found to be miscible in accordance with morphology and thermal transition criteria of polymer miscibility. Miscibility of the pair poly(phenyl methacrylate) and poly‐(benzyl methacrylate) is quite unusual. Interactions between carbonyl units and phenyl rings of these two polymers are discussed. FT‐IR results indicate an intimate mixing state between these two polymers leading to mutual influence in the absorbance wavenumbers for C=O, ether groups and, possibly, phenyl rings.     

Perfluorophenyl‐Bifuran: A Stable and Fluorescent Material Exhibiting Mechanofluorochromic Behavior

π‐Conjugated oligomers and polymers consisting of bifuran units are applied in optoelectronic devices, because bifuran units endow such devices with superior properties compared with their thiophene analogs. However, as is true for most furan oligomers, bifuran oligomers suffer from low photostability, which restricts their application. In this work, we present the synthesis and the photophysical and structural characterization of perfluorinated phenyl bifuran ( PFB‐2F ), which displays high photostability, while maintaining strong fluorescence quantum efficiency in both solution and the solid state. X‐Ray crystallography reveals that, unlike its thiophene analog, PFB‐2F has a completely planar backbone, with slip‐stacked packing and short interplanar distances. PFB‐2F crystals display mechanofluorochromic behavior, which renders perfluorophenyl‐substituted oligofurans potential candidates for both stable optoelectronic devices and responsive optical materials.     

Formation of Azulene‐Embedded Nanographene: Naphthalene to Azulene Rearrangement During the Scholl Reaction

Incorporation of a non‐hexagonal ring into a nanographene framework can lead to new electronic properties. During the attempted synthesis of naphthalene‐bridged double [6]helicene and heptagon‐containing nanographene by the Scholl reaction, an unexpected azulene‐embedded nanographene and its triflyloxylated product were obtained, as confirmed by X‐ray crystallographic analysis and 2D NMR spectroscopy. A 5/7/7/5 ring‐fused substructure containing two formal azulene units is formed, but only one of them shows an azulene‐like electronic structure. The formation of this unique structure is explained by arenium ion mediated 1,2‐phenyl migration and a naphthalene to azulene rearrangement reaction according to an in‐silico study. This report represents the first experimental example of the thermodynamically unfavorable naphthalene to azulene rearrangement and may lead to new azulene‐based molecular materials.     

Pyrrolo‐dC Metal‐Mediated Base Pairs in the Reverse Watson–Crick Double Helix: Enhanced Stability of Parallel DNA and Impact of 6‐Pyridinyl Residues on Fluorescence and Silver‐Ion Binding

Reverse Watson–Crick DNA with parallel‐strand orientation (ps DNA) has been constructed. Pyrrolo‐dC (PyrdC) nucleosides with phenyl and pyridinyl residues linked to the 6 position of the pyrrolo[2,3‐d]pyrimidine base have been incorporated in 12‐ and 25‐mer oligonucleotide duplexes and utilized as silver‐ion binding sites. Thermal‐stability studies on the parallel DNA strands demonstrated extremely strong silver‐ion binding and strongly enhanced duplex stability. Stoichiometric UV and fluorescence titration experiments verified that a single ^2pyPyrdC–^2pyPyrdC pair captures two silver ions in ps DNA. A structure for the PyrdC silver‐ion base pair that aligns 7‐deazapurine bases head‐to‐tail instead of head‐to‐head, as suggested for canonical DNA, is proposed. The silver DNA double helix represents the first example of a ps DNA structure built up of bidentate and tridentate reverse Watson–Crick base pairs stabilized by a dinuclear silver‐mediated PyrdC pair.     

A Masked Cuprous Hydride as a Catalyst for Carbonyl Hydrosilylation in Aqueous Solutions

Redox‐unstable cuprous hydridotriphenylborate was isolated as an N‐heterocyclic carbene adduct [(IPr)Cu(HBPh₃)] (IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene) with good thermal stability. Although this compound displays a contact ion‐pair structure, Cu^IH‐like catalytic activity was envisaged in carbonyl hydrosilylation. Sufficient moisture stability allowed the catalysis in aqueous/organic media. Mechanistic study further showed that a phenyl group on the borate anion is abstracted by [(IPr)Cu]⁺ to give the cationic organocopper complex [(IPr)₂Cu₂(μ‐Ph)][BPh₄].     

A route toward multifunctional polyurethanes using triple click reactions

The aliphatic polyurethane with pendant alkyne, perfluorophenyl, and anthracene moieties (PU‐anthracene) was prepared from polycondensation of anthracene, alkyne, and perfluorophenyl functional‐diols with hexamethylenediisocyanate in the presence of dibutyltindilaurate (DBTL) in CH₂Cl₂ at room temperature for 10 days. Thereafter, the PU‐(anthracene‐co‐alkyne‐co‐perfluorophenyl) (M_n,GPC = 15,400 g/mol, M_w/M_n= 1.37, relative to PS standards) was sequentially clicked with benzyl azide, octylamine, and 4‐(2‐hydroxyethyl)?10‐oxa‐4‐azatricyclo[5.2.1.02,6]dec‐8‐ene‐3,5‐dione (adduct alcohol) via copper‐catalyzed azide‐alkyne cycloaddition, active ester substitution and Diels–Alder reactions, respectively, to finally yield PU‐(hydroxyl‐co‐benzyltriazole‐co‐octylamine). The PUs were characterized using ¹H NMR, GPC, and DSC. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 480–486     

Synthesis of a New Chiral Source, (1R,2S)‐1‐Phenylphospholane‐2‐carboxylic Acid,via a Key Intermediate α‐Phenylphospholanyllithium Borane Complex: Configurational Stability and X‐ray Crystal Structure of an α‐Monophosphinoalkyllithium Borane Complex

A synthetic route to enantiomerically pure (1R,2S)‐1‐phenylphospholane‐2‐carboxylic acid ( 1 ), which is a phosphorus analogue of proline, has been established. A key step is the deprotonation–carboxylation of the 1‐phenylphospholane borane complex 3 by using sBuLi/1,2‐dipiperidinoethane (DPE). Configurational stability of the key intermediate, the amine‐coordinated α‐phosphinoalkyllithium borane complex 4 , was investigated by employing lithiodestannylation–carboxylation of both diastereomers of the 1‐phenyl‐2‐trimethylstannylphospholane borane complex 7 in the presence of several kinds of amines, and as a result, 4 was found to be configurationally labile even at ?100 °C. The key intermediate, the DPE‐coordinated trans‐1‐phenyl‐2‐phospholanyllithium borane complex 9 , was isolated, and the structure was identified by X‐ray crystal structure analysis. This is the first X‐ray crystal structure determined for an α‐monophosphinoalkyllithium borane complex. Remarkably, the alkyllithium complex is monomeric and tricoordinate at the lithium center with a slightly pyramidalized environment, and the existence of a Li? C bond (2.170 Å) has been confirmed. Moreover, ¹H–⁷Li HOESY and ⁶Li NMR analyses suggested the structure of 9 in solution as well as the existence of an equilibrium between 9 , its cis isomer, and the ion pair 8 at room temperature, which was extremely biased towards 9 at ?100 °C. Finally, 1 was used as a chiral ligand in a palladium‐catalyzed allylic substitution, and the desired product was obtained in high yield with good enantioselectivity.     

Synthesis,characterization, and electroluminescence of polyfluorene copolymers containing T‐shaped isophorone derivatives

We have successfully synthesized a series of new fluorene‐based copolymers, poly[(9,9‐bis(4‐octyloxy‐phenyl)fluorene‐2,7‐diyl)‐co‐[2(3{2[4(2{4[bis(bromophenyl‐4yl) amino]phenyl}vinyl)‐2,5‐bisoctyloxyphenyl]vinyl}‐5,5‐dimethyl‐cyclohex‐2‐enylidene)malononitrile] (PFTBMs), with varying molar ratios of the low‐energy band gap comonomer, 2(3{2[4(2{4[bis(4‐bromophenyl)amino]phenyl}vinyl)‐2,5‐bisoctyloxyphenyl]vinyl}‐5,5‐dimethyl‐cyclohex‐2‐enylidene)malononitrile (BTBM). To prepare BTBM (which has a T‐shaped structure) from triphenylamine, dialkoxy phenyl, and isophorone, we introduced three individual segments of an isophorone derivative containing two cyanide groups at the carbonyl position, a dialkoxy phenyl group for increased solubility, and a triphenyl amine for effective charge transfer. Furthermore, we introduced vinyl linkages between each segment to increase the length of π‐conjugation. The synthesized polyfluorene copolymers with the BTBM, PFTBMs, were synthesized via palladium‐catalyzed Suzuki coupling reactions. The photoluminescence emission spectra of the synthesized polymers in solution did not show significant energy transfer from PBOPF segments to the BTBM units. Light‐emitting devices based on these polymers were fabricated with an indium tin oxide/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/polymers/Balq/LiF/Al configuration. Examination of the electroluminescence emission of the synthesized polymers showed that the maximum wavelength shifted continuously toward long wavelengths with as the number of BTBM units in the polymer main chain was increased. In particular, a device using PFTBM 05 exhibited a maximum brightness of 510 cd/m² and a maximum current efficiency of 0.57 cd/A. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 82–90, 2010     

Reactivity of Lewis Basic Platinum Complexes Towards Fluoroboranes

We herein report detailed investigations into the interaction of Lewis acidic fluoroboranes, for example BF₂Pf (Pf=perfluorophenyl) and BF₂Ar^F (Ar^F=3,5‐bis(trifluoromethyl)phenyl), with Lewis basic platinum complexes such as [Pt(PEt₃)₃] and [Pt(PCy₃)₂] (Cy=cyclohexyl). Two presumed Lewis adducts could be identified in solution and corresponding secondary products of these Lewis adducts were characterized in the solid state. Furthermore, the concept of frustrated Lewis pairs (FLP) was applied to the activation of ethene in the system [Pt(BPf₃)(CH₂CH₂)(dcpp)] (dcpp=1,3‐bis(dicyclohexylphosphino)propane; Pf=perfluorophenyl). Finally, DFT calculations were performed to determine the interaction between the platinum‐centered Lewis bases and the boron‐centered Lewis acids. Additionally, several possible mechanisms for the oxidative addition of the boranes BF₃, BCl_3, and BF₂Ar^F to the model complex [Pt(PMe₃)₂] are presented.     

Ge=B π‐Bonding: Synthesis and Reversible [2+2] Cycloaddition of Germaborenes

Phosphine‐stabilized germaborenes featuring an unprecedented Ge=B double bond with short B???Ge contacts of 1.886(2) ( 4 ) and 1.895(3) Å ( 5 ) were synthesized starting from an intramolecular germylene–phosphine Lewis pair ( 1 ). After oxidative addition of boron trihalides BX₃ (X=Cl, Br), the addition products were reduced with magnesium and catalytic amounts of anthracene to give the borylene derivatives in yields of 78 % ( 4 ) and 57 % ( 5 ). These halide‐substituted germaborenes were characterized by single‐crystal structure analysis, and the electronic structures were studied by quantum‐chemical calculations. According to an NBO NRT analysis, the dominating Lewis structure contains a Ge=B double bond. The germaborenes undergo a reversible, photochemically initiated [2+2] cycloaddition with the phenyl moiety of a terphenyl substituent at room temperature, forming a complex heterocyclic structure with Ge^IV in a strongly distorted coordination environment.     

Structure and dynamic features of an intramolecular frustrated Lewis pair

Di(mesityl)cyclohexenylphosphine undergoes hydroboration with Piers' borane [HB(C₆F₅)₂] to yield the cyclohexylene‐anellated frustrated Lewis pair 5 . This P/B pair splits H₂ with the formation of the product 4 and adds to the C?O double bond of phenyl isocyanate to yield 6 . In the crystal, compound 5 features a puckered four‐membered heterocyclic core structure with a long P? B bond (av. 2.197(5) Å). The activation energy of the P? B cleavage of the frustrated Lewis pair 5 was determined by dynamic ¹⁹F NMR spectroscopy at ΔG^≠(298 K)=12.1±0.3 kcal mol^?1.     

Tuning the Photophysical Properties and Solid‐State Organization of Perfluorophenyl‐functionalized Dithieno[3,2‐b:2′,3′‐d]phospholes

A series of perfluorophenyl‐substituted dithienophosphole derivates has been synthesized. Investigation of their photophysical properties, as well as their organization in the solid state reveals that these properties can be manipulated via introduction of bromine substituents in 2,6‐position of the dithienphosphole scaffold, as well as the complexation of the phosphorus center with an electron rich gold(I) fragment. The strongly electron‐withdrawing character of the perfluorophenyl‐group surmounts the effect of the oxidation of the phosphorus center with respect to photophysics, leading to leading to optoelectronic features similar to those of the trivalent phosphole species. The trivalent phosphole species. The solid‐state organization of the members of this perfluorinated dithienophosphole family, on the other hand, strongly depends on the heteroatoms present within the system, as close intermolecular interactions can be observed between varieties of different atoms (Au‐Au, Br‐Br, Br‐O, Br‐C, F‐C, O‐S), next to regular C‐C π‐stacking interactions.     

Anion‐Binding Catalysis by Electron‐Deficient Pyridinium Cations

A new activation principle in organocatalysis is presented: halide binding through Coulombic interactions. This mode of catalysis was realized by using 3,5‐di(carbomethoxy)pyridinium ions that carry an additional electron‐withdrawing substituent on the nitrogen atom, for example, pentafluorobenzyl or cyanomethyl. For the N‐pentafluorobenzyl derivative, Coulombic interaction with the pyridinium moiety is complemented in the solid state by anion–π interactions with the perfluorophenyl ring. Bromide and chloride are bound by these cations in a 1:1 stoichiometry. Catalysis of the C? C coupling between 1‐chloroisochroman (and related electrophiles) with silyl ketene acetals occurs at ?78 °C and at low catalyst loading (2 mol %).     

An efficient synthesis of new class of pyrazolo[3,4‐b]pyridine‐6‐one derivatives by a novel cascade reaction

A novel cascade reaction of 4‐arylidene‐2‐phenyl‐1,3‐oxazol‐5(4H)‐one with 3‐methyl‐1‐phenyl‐1H‐pyrazol‐5‐amine was described and a number of new pyrazolo[3,4‐b]pyridine‐6‐one derivatives were synthesized. This new protocol has the advantages of shorter time, higher yields, and lower cost as well as easier operation.     

Photophysical and Laser Properties of Cassettes based on a BODIPY and Rhodamine Pair

This work deals with the synthesis and the photophysical and laser properties of new BODIPY‐rhodamine cassettes. These dyads differ in their rigid and conjugated spacer group (phenyl or acetylenephenyl) and in their linking positions (meta or para). The photophysical properties of these cassettes are controlled by the formation/opening of the spirolactone ring, which, in turn, switches off/on an energy‐transfer process between the chromophores. Herein, we thoroughly describe the influence of the attached spacer group, as well as the distance and orientation between the donor–acceptor pair, on the excitation energy transfer. The observed fast dynamics and efficiency suggest that the process mainly takes place “through‐bond”, although the “through‐space” mechanism also contributes to the whole process. As a result, efficient laser emission from the rhodamine is achieved upon excitation of the BODIPY, in particular for the cassette that contains an acetylenephenyl spacer group in a para disposition.     

Extended triphenylamine conjugated systems derivatized by perfluorophenyl groups

Two triphenylamine derivatives bearing terminal perfluorophenyl groups have been synthesized. Their HOMO, LUMO levels and electronic band gap have been evaluated by spectroscopic and electrochemical measurements and rationalized with theoretical calculations. X-ray structure analysis of crystals allowed the observation of multiple intermolecular interactions due to the presence of the perfluorophenyl pendant groups. The multiplication of these interactions explains the differences between calculated (in gas phase) and observed (in solid states) structures.     

Theoretical Study of the Stability of the DNA Duplexes Modified by a Series of Hydrophobic Base Analogues

The geometries of a 13 mer of a DNA double helix (5′‐GCGTAC A CATGCG‐3′) were determined by molecular dynamics simulations using a Cornell et al. empirical force field. The bases in the central base pair (shown in bold) were replaced (one or both) by a series of hydrophobic base analogues (phenyl, biphenyl, phenylnaphathalene, phenylanthracene and phenylphenanthrene). Due to the large fluctuations of the systems, an average geometry could not be determined. The interaction energies of the Model A, which consisted of three central steps of a duplex without a sugar phosphate backbone, taken from molecular dynamics simulations (geometry sampled every 1 ps), were calculated by the self‐consistent charge density functional based tight‐binding (SCC‐DFTB‐D) method and were subsequently averaged. The higher the stability of the systems the higher the aromaticity of the base analogues. To estimate the desolvation energy of the duplex, the COSMO continuum solvent model was used and the calculations were provided on a larger model, Model B (the three central steps of the duplex with a sugar phosphate backbone neutralised by H atoms), taken from molecular dynamics simulations (geometry sampled every 200 ps) and subsequently averaged. The selectivity of the base analogue pairs was ascertained (Model B) by including the desolvation energy and the interaction energy of both strands, as determined by the SCC‐DFTB‐D method. The highest selectivity was found for a phenylphenanthrene. Replacing the nucleic acid bases with a base analogue leads to structural changes of the central pair. Only with the smallest base analogues (phenyl) does the central base pair stay planar. When passing to larger base analogues the central base pair is usually stacked.