Acetylene Spacer Research Articles

Optical Properties of DMA-π-DCV Derivatives: A Theoretical Inspection under the DFT Microscope

The optical properties of a series of donor-acceptor N,N-dimethylaniline-π-dicyanovinylene (DMA-π-DCV) chromophores have been investigated under the density functional theory framework. Focus has been made on the low-lying charge-transfer (CT) electronic transitions for which experimental data is available. The effect of theπ-conjugated bridge length and type was analysed between the families of oligoene and oligoyne derivatives of increasing size. Theoretical calculations demonstrate that the ethylene bridge is a betterπ-communicator and allows for more delocalized frontier molecular orbitals compared to the acetylene spacer. TheΛdiagnostic test allowed rationalization of the orbital spatial overlap in the main CT excitations. The performance of different density functional rungs was assessed in the prediction of the lowest-lying CT electronic transition. Surprisingly, most modern long-range corrected functionals demonstrated to provide among the largest errors, whereas hybrid functionals showed the best performance. Solvatochromism was confirmed in both oligoene and oligoyne compounds. A donor-acceptor-donor triad based on tetrathiafulvalene was utilised as a test system for the prediction of its two CT bands of different nature, energy, and intensity. The hybrid PBE0 (or a similar hybrid analogue) consolidates as the best choice for the prediction of CT excitations in the DMA-π-DCV push-pull family.

Self-Assembly of Four-Claw Discotic Mesogenic Molecules: Influence of Core on Chirality

The morphology of self-assembled monolayers determined by molecular structure and involved interactions plays a crucial role in their properties. Herein, we report a study on 2D self-assembly of two kinds of triphenylene-submitted discotic mesogenic species, which have similar four TP moieties with alkyne spacer but different rigid aromatic cores pyrene and carbazole. Two types of stable periodic long-ranged supramolecular networks on the highly oriented pyrolytic graphite surface have been visualized via high-resolution scanning tunneling microscopy technique. A comparative study reveals how the aromatic core of molecular building blocks affects achiral and chiral arrangement of discotic molecule on surface. The asymmetry backbone results in molecular orientation and varied van der Waals forces between molecule–molecule and molecule–substrate. Our results demonstrate that design of functional molecules plays an important role in the construction of 2D supramolecular assembly possessing desirable structur...

Two Symmetrically Bis‐substituted Pyrene Derivatives: Synthesis, Photoluminescence, and Electroluminescence

AbstractTwo kinds of cyanophenyl terminated pyrene derivatives for organic light‐emitting diodes were synthesized and characterized by UV/Vis, fluorescence (FL), 1H NMR, MALDI‐TOF, CV and TGA. Both compounds exhibited blue photoluminescence and high fluorescent quantum yield of 85% and 75% in solutions. Due to the presence of acetylene spacer, the compound distinguishes itself by high coplanarity, high thermal stability, little Stokes' shift and clear excimer formation in the solid state from the acetylene‐free compound. In order to suppress the molecular aggregation, the electroluminescent properties were studied by doing the materials in PVK. The result proved that energy transfer happened from the host PVK to the materials.

Synthesis and biological evaluation of novel allosteric enhancers of the A1 adenosine receptor based on 2-amino-3-(4'-chlorobenzoyl)-4-substituted-5-arylethynyl thiophene.

A Sonogashira coupling strategy was employed to synthesize a new series of allosteric modulators for the A1 adenosine receptor based on the 2-amino-3-(p-chlorobenzoyl)-4-substituted thiophene skeleton, with a two-carbon (rigid or flexible) linker between the 5-position of the thiophene ring and a (hetero)aryl or alkyl moiety. Among the compounds characterized by the presence of a common phenylacetylene moiety at the 5-position of the thiophene ring, the neopentyl substitution at the 4-position supported a strong activity. In the series of 4-neopentyl derivatives, the presence of an acetylene spacer at the 5-position of the thiophene is optimal for activity, whereas reduction of the acetylene to an ethyl moiety decreased activity, both in functional and binding assays. Derivatives 4e, 4g-h, 4j, 4l, and 4m were the most promising compounds in binding (saturation and competition) and functional cAMP studies, being able to potentiate agonist [(3)H]CCPA binding to the A1 receptor, with 4e as the best compound of the series. The latter compound also retarded the dissociation of another radiolabeled agonist, [(3)H]NECA, from the receptor.

Polymerization behavior and gel properties of ethane, ethylene and acetylene-bridged polysilsesquioxanes

Soluble bridged polysilsesquioxanes with a range of molecular weight were synthesized from bis(triethoxysilyl)ethane, ethylene, and acetylene (BTES-E1, -E2, and -E3) via hydrolysis and polycondensation reaction by adjusting the water amount. Polymerization behavior of these three trialkoxysilanes was investigated by monitoring the reaction progress by GPC, and 29Si NMR spectrometry of the resulting polymers, poly(BTES-E1), poly(BTES-E2), and poly(BTES-E3), showing that BTES-E1 generated cyclic oligomers at the early stage. In contrast, polymerization of BTES-E2 and BTES-E3 provided no detectable amounts of cyclic oligomers, but afforded linear polymers only. Bulk gels were also prepared by curing the polymers. The gel from poly(BTES-E3) exhibited high thermal stability derived from the rigid acetylene spacer with respect to thermogravimetric analysis. On the other hand, the polymer film of BTES-E1 showed the highest pencil hardness index among the polymers, indicating the tight siloxane network of poly(BTES-E1).

Donor–Acceptor (D–A)‐Substituted Polyyne Chromophores: Modulation of Their Optoelectronic Properties by Varying the Length of the Acetylene Spacer

A series of donor-acceptor-substituted alkynes, 2 a-f, was synthesized in which the length of the π-conjugated polyyne spacer between the N,N-diisopropylanilino donor and the 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) acceptor was systematically changed. The effect of this structural change on the optoelectronic properties of the molecules and, ultimately, their third-order optical nonlinearity was comprehensively investigated. The branched N,N-diisopropyl groups on the anilino donor moieties combined with the nonplanar geometry of 2 a-f imparted exceptionally high solubility to these chromophores. This important property allowed for performing INADEQUATE NMR measurements without (13) C labeling, which, in turn, resulted in a complete assignment of the carbon skeleton in chromophores 2 a-f and the determination of the (13) C-(13) C coupling constants. This body of data provided unprecedented insight into characteristic (13) C chemical shift patterns in push-pull-substituted polyynes. Electrochemical and UV/Vis spectroscopic studies showed that the HOMO-LUMO energy gap decreases with increasing length of the polyyne spacer, while this effect levels off for spacers with more than four acetylene units. The third-order optical nonlinearity of this series of molecules was determined by measuring the rotational averages of the third-order polarizabilities (γrot ) by degenerate four-wave mixing (DFWM). These latter studies revealed high third-order optical nonlinearities for the new chromophores; most importantly, they provided fundamental insight into the effect of the conjugated spacer length in D-A polyynes, that can be exploited in the future design of suitable charge-transfer chromophores for applications in optoelectronic devices.

An Acetylene-Containing Perylene Diimide Copolymer for High Mobility n-Channel Transistor in Air

A new solution-processable conjugated copolymer (P1) of perylene diimide (PDI) and dithienothiophene (DTT) incorporating acetylene spacers was synthesized by palladium(0)-catalyzed Sonogashira coupling reaction. Theory calculation reveals that introduction of rod-like ethynylene spacer in the polymer main chain promotes planarity and π-conjugation of the polymer main chain. Relative to the conjugated copolymer (P2) of PDI and DTT without acetylene spacers, polymer P1 exhibits 0.1 eV down shift of LUMO level and 89 nm red shift of low-energy absorption band. Polymer P1 in top-contact bottom-gate organic field-effect transistors (OFETs) exhibits a saturation electron mobility of 0.06 cm2 V–1 s–1 in air, while P2 does not function in the same device in air. Additionally, a saturation electron mobility of 0.075 cm2 V–1 s–1 in air, and after six days storage in air, an electron mobility of 0.034 cm2 V–1 s–1 were observed for P1 in bottom-contact bottom-gate OFETs; while a saturation electron mobility of 0.038 cm2 V–1 s–1 in air, and after six days storage in air, an electron mobility of 0.013 cm2 V–1 s–1 were observed for P2 in the same device. The better air stability and higher electron mobility of P1 are attributed to densely ordered packing of the polymer chains excluding oxygen or water and the lower LUMO level of P1.

Novel planar and star-shaped molecules: Synthesis, electrochemical and photophysical properties

Three novel planar and star-shaped molecules containing thiophene-functionalized group and acetylenic spacers, 4-((5″-iodo-[2,2′:5′,2″-terthiophen]-5-yl)ethynyl)aniline (I3TEA), 4,4′-([2,2′:5′,2″-terthiophene]-5,5″-diylbis(ethyne-2,1-diyl))dianiline (3TDDA), 1,3,5-tris((5-((trimethylsilyl)ethynyl)thiophen-2-yl)ethynyl)benzene (TETEB) were synthesized through Sonogashira coupling reaction. Their photophysical and electrochemical properties were explored by UV–vis, photoluminescence (PL) emission and DFT calculation. Three compounds possess unusual phenomena of PL, with the concentration of gradually decreased, the intensity of PL firstly increased and then decreased, this may be due to the aggregate-enhanced emission (AEE) effect and aggregation-caused quenching (ACQ) effect. Their spectroscopic data demonstrate that D–π–A–π–D structured organic dye 3TDDA based on NH2 as donor units and 3T as acceptor units with acetylenic spacers π-conjugated chain between them exhibits good luminescent properties. Dye I3TEA with donor(D)–acceptor(A) structure shows good charge transfer because of amino functional group and iodine atom. Octupolar organic π-conjugated star-shaped molecule TETEB possesses excellent luminescent properties because of its unique structure applied in the optoelectronic field. The redox curves and results of DFT calculations suggest that three compounds have low ionization potential and low Eoxd. All the good properties demonstrate three compounds could be promising candidates for photovoltaic materials.

Novel phenyl-oligothiophene derivatives containing acetylenic spacers for thin film materials: Synthesis, photophysical and morphology properties

Abstract Four novel organic semiconductor phenyl-oligothiophene derivatives containing acetylenic spacers, 5-(phenylethynyl)-2,2′:5′,2″-terthiophene, 5-(phenylethynyl)-2,2′:5′,2″:5″,2‴-quaterthiophene, 4-([2,2′:5′,2″-terthiophen]-5-ylethynyl)aniline, 4-((5′-iodo-[2,2′-bithiophen]-5-yl)ethynyl)aniline were synthesized and studied with respect to their thermal, photophysical, electrochemical and morphological properties. TGA and DSC results show all the oligomers have good thermal stability. Electrochemical measurements suggest the compounds can be used as photovoltaic materials. UV–vis spectra confirm all the molecules adopt close side-to-side packing, indicating H-aggregation. 4-([2,2′:5′,2″-Terthiophen]-5-ylethynyl)aniline exhibits excellent fluorescence properties when applied in an optoelectric field. XRD analysis indicates that the four compounds have a high degree of lamellar ordering and crystallinity. Film morphology properties reveal a clearly single-crystalline monoclinic morphology with lamellae parallel to the substrate, exhibiting that adjacent molecules have a strong intermolecular interaction. The potential liquid crystalline property is illustrated by DSC, XRD and polarization optical microscopy. These properties demonstrate that these oligomers could be promising candidates for the organic thin film materials and photovoltaic devices.

Improvement of anhydrous catalyst stability in acetylene dimerization by regulating acidity

AbstractBACKGROUND: Loss of the active CuCl component occurs during acetylene dimerisation to monovinylacetylene (MVA) catalysed by an anhydrous catalyst with the formation of a dark red precipitate. Acidic species can reduce the loss of CuCl but have an unfavorable influence on acetylene dimerisation. This study aims to determine the precipitate composition and regulate the acidity of the catalyst to find a balance between reaction rate, MVA selectivity and catalyst life.RESULT: The precipitate composition was 2CuCl·3C2H2·1/3CH3CH2NH2·1/7C3H7NO, formed by the combination of DMF, CH3CH2NH2, C2H2 and the [Cu]‐acetylene π‐complex, which is an intermediate in the reaction. From an overall consideration of the loss of CuCl, conversion of acetylene, and selectivity of MVA, the reaction temperature and acetylene space velocity were optimized at 65 °C and 200 h−1, respectively. The introduction of HCl into the catalyst with a rate of 3.2 h−1 could reduce CuCl loss by 73.5%, whereas conversion of acetylene was only lowered by 9.0%.CONCLUSION: Acidity regulation of the anhydrous catalyst by optimising the reaction temperature, acetylene space velocity, and rate of addition of HCl shows little negative effect on acetylene conversion and selectivity to MVA but can reduce CuCl loss significantly. © 2012 Society of Chemical Industry

Click chemistry on self-assembled monolayer of zeolite L crystals by microcontact printing – Applications in nanobiotechnology

Self assembled monolayers (SAMs) of zeolite L crystals were functionalized with fluorescent dye molecules or bioactive carbohydrate using microcontact printing (mCP). Fluorescent molecules such as lissamine rhodamine (LRA) and sugars such as α- d-mannoside (α- d-Man) functionalized with a terminal acetylene spacer were immobilized by “click” reaction on the top side of an azide functionalized zeolite L monolayer. Patterned and non-patterned SAMs of α- d-Man functionalized zeolite were used for cell adhesion and cellular patterning.

Synthesis and spectral properties of new 3,3’-bis(dipyrrolylmethene) with acetylene spacer

Bis(2,4,7,9-tetramethyl-8-ethyldipyrrolylmethen-3-yl)acetylene dihydrobromide (H2L·2HBr), new bis(dipyrrolylmethene), in whose molecule dipyrrolylmethene domains were connected through 3,3′-carbon atoms of internal pyrrole nuclei by acetylene spacer, were synthesized by original procedure. The compound was characterized by element analysis, IR, 1H NMR, and electronic spectroscopy. The comparative analysis of spectral properties shows the reduction of the basicity of H2L ligand in comparison with the structural analogs, which contain internal methylene spacer. The quantum-chemical simulation showed that the rigid acetylene spacer gives linear structure to the H2L molecule in contrast to the spiral-shaped geometry of structural analogs with -CH2- spacer.

Synthesis and Properties of 1,8-Carbazole-Based Conjugated Copolymers

A new series of conjugated carbazole polymers based on the 1,8-carbazolylene unit was synthesized by the Pd-catalyzed polycondensation between the 1,8-diiodocarbazole derivative and various bifunctional counter comonomers. An alkyne spacer was found to be a key to increasing the molecular weight of the resulting polymers. All the obtained polymers showed good solubilities in the common organic solvents, and they were fully characterized by Gel permeation chromatography (GPC), and 1H NMR and infrared (IR) spectroscopies. The UV-vis absorption and fluorescence spectra revealed the relationship between the chemical structure and effective conjugation length. The efficiency order of the carbazole connectivity was 2,7-carbazolylene > 1,8-carbazolylene > 3,6-carbazolylene. The electrochemical properties of these polymers suggested the relatively facile oxidation at ca. +0.5–0.7 V vs. Fc/Fc+ or a high potential as p-type semiconductors. The combination of the electrochemical oxidation potentials and the optical band gaps allowed us to estimate the HOMO and LUMO levels of the polymers. It was shown that the energy levels of the 1,8-carbazole-based conjugated polymers can be tunable by selecting the appropriate comonomer structures.

ChemInform Abstract: Acceleration of Photoinduced Charge Separation in Porphyrin-C60 Dyad with an Acetylene Spacer.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

How Strained are Carbomeric-Cycloalkanes?

The ring strain energies of carbomeric-cycloalkanes (molecules with one or more acetylene spacer units placed into carbon single bonds) are assessed using a series of isodesmic, homodesmotic, and hyperhomodesmotic chemical equations. Isodesmic bond separation reactions and other equations derived from the explicitly defined hierarchy of homodesmotic equations are insufficient for accurately determining these values, since not all perturbing effects (i.e., conjugation and hyperconjugation) are fully balanced. A set of homodesmotic reactions is proposed, which succeeds in balancing all stereoelectronic effects present within the carbomeric rings, allowing for a direct assessment of the strain energies. Values calculated from chemical equations are validated using an increment/additivity approach. The ring strain energy decreases as acetylene units are added, manifesting from the net stabilization gained by opening the C-CH(2)-C angle around the methylene groups and the destabilization arising from bending the C-C identical withC angles of the spacer groups. This destabilization vanishes with increasing parent ring size (i.e., the angle distortion is less in the carbomeric-cyclobutanes than in the carbomeric-cyclopropanes), leading to strain energies near zero for carbo(n)-cyclopentanes and carbo(n)-cyclohexanes.

The cytotoxic styryl lactone goniothalamin is an inhibitor of nucleocytoplasmic transport

An in vivo nuclear export assay (immunostaining of Rio2 in HeLa cells) demonstrated that ( R)-goniothalamin is an inhibitor of nucleocytoplasmic transport above 500 nM, which was rationalized also by molecular modeling. The cytotoxic styryl lactone natural product was prepared via an enantioselective Cr(III) catalyzed hetero Diels–Alder reaction and a Sonogashira coupling. A series of analogs was synthesized and only the oxidized goniothalamin derivative featuring an alkyne spacer was found active. Unsaturated lactones of natural origin other than leptomycin (LMB) are thus suggested to operate via a similar mechanism targeting the CRM1 nuclear receptor.

Acetylenic spacers in phenylene end-substituted oligothiophene core for highly air-stable organic field-effect transistors

Two thiophene-phenylene semiconductors, bis(2-phenylethynyl) end-substituted oligothiophenes (diPhAc-nTs, n = 2, 3), were synthesized and studied with respect to their optical, electrochemical, structural and electrical properties. The optical and electrochemical properties of the oligomers in solution were investigated by UV-vis absorption and photoluminescence spectroscopies, and cyclic voltammetry. High vacuum evaporated thin films were investigated by optical absorption, X-ray diffraction and AFM, and implemented as p-type semiconducting layers into organic thin-film transistors (OTFTs). A comparative study in solution and in the solid state with distyryl-oligothiophenes (DSnTs, n = 2, 3) reveals the great influence of acetylenic (-C[triple bond]C-) vs. olefinic (-C=C-) spacers in thiophene-phenylene derivatives on electronic structure, physical properties, and device efficiencies. Substituting olefinic for acetylenic pi-spacers in terthiophene-based conjugated semiconductors leads to one of incontrovertible attributes of OTFTs for low cost applications, a high mobility at low substrate temperature (T(sub)) i.e. typically 25 degrees C. Fine-tuning in the HOMO/LUMO levels by reducing the HOMO level introduces increased air-oxidation strength of thin films where OTFTs provide exactly the same hole mobility value after 100 days in air. All the results suggested that introduction of carbon-carbon triple bonds provided an efficient route to highly air-stable organic thin film transistors.

Comparative structural and thermodynamic studies of fluoride and cyanide binding by PhBMes2 and related triarylborane Lewis acids

Lewis acidic boranes containing the –BMes2 unit (Mes = 2,4,6-Me3C6H2) have been widely exploited in molecular sensors for the fluoride ion reflecting, at least in part, the stability to air and moisture of derivatives of the type ArBMes2. In the current study, the fluoride binding capabilities of the simplest such system, PhBMes2 (1), have been investigated by spectroscopic and crystallographic methods, with a view to experimentally determining the fundamental thermodynamic and structural parameters associated with this host/guest interaction. A binding constant, KF, of 8.9(1.9) × 104 M−1 in dichloromethane solution and a B–F bond length of 1.481(2) A for the salt [nBu4N]+[PhMes2BF]− have thus been elucidated and provide a baseline for the analysis of more complex systems. Competitive binding of the cyanide ion is implied by a similar binding constant, KCN, of 1.9(0.5) × 105 M−1; structurally, similar degrees of pyramidalization of the BC3 framework are observed on coordination of each anion {Σ(C–B–C) = 339.8, 340.1° for [nBu4N]+[PhMes2BF]− and [K(18-crown-6)]+[PhMes2BCN]−, respectively}. Linking of two ArBMes2 units via an alkyne spacer results in a 2,2′-bis(dimesitylboryl)tolan system, which is characterized by independent binding of two equivalents of the CN− anion, rather than cyanide chelation.

Synthesis and Properties of Conjugated Poly(1,8-carbazole)s

During our search of novel conjugated carbazole polymers, we succeeded in the efficient synthesis of conjugated poly(1,8-carbazole) derivatives. The synthetic route to the 1,8-difunctionalized carbazole monomers and the polymerization methods under the Yamamoto, Sonogashira, and Hay conditions were established. The obtained poly(1,8-carbazole)s were comprehensively characterized by GPC, MALDI-TOF MS, 1H NMR, and IR spectroscopies, and it was found that the alkyne spacer is an important factor in obtaining the high molecular weight polymers. Thermal analysis revealed that the alkyne-linked poly(1,8-carbazole)s possess a higher thermal stability than the directly linked poly(1,8-carbazole). The energy diagrams of a series of polycarbazoles were carefully estimated from the electrochemical and optical measurements. The alkyne-linked carbazole polymers were potent blue-light-emitting polymers due to their narrow band gaps. Furthermore, the remarkable decreased aggregation behavior of the butadiynylene-linked ...

Alkyne-Linked 2,2-Disubstituted-indolin-3-one Oligomers as Extended β-Strand Mimetics

The design, synthesis, and structural analysis of a new foldamer that mimics an extended beta-sheet are presented. The nonpeptidic mimetic is based on a series of 2,2-disubstituted-indolin-3-one groups linked through their 4,7-positions by an alkyne spacer. An intramolecular hydrogen bond between the carbonyl of one indolinone subunit and the proximal NH of another subunit imposes a conformation that mimics the side chain positioning on a beta-strand. X-ray crystallographic studies support the presence of this intramolecular hydrogen bond. The described approach allows extension of the scaffold to longer oligomers that will form the basis of new mimetics for the disruption of therapeutically relevant protein-protein interactions that rely on the contacts of side chain residues on two beta-strands.