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Spacer Length (spacer + length)
Kinds of Spacer Length Selected AbstractsConstruction of 1D and 2D Copper(I) Coordination Polymers Assembled by PhS(CH2)nSPh (n = 1, 2) Dithioether Ligands: Surprising Effect of the Spacer Length on the Dimensionality, Cluster Nuclearity and the Fluorescence Properties of the Metal,Organic Framework,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2007Harmel N. Peindy Abstract Treatment of CuI with PhSCH2SPh in MeCN solution affords, by a self-assembly reaction, the monodimensional metal,organic coordination polymer [Cu4I4{,-PhS2CH2SPh}2]n (1), in which Cu4(,3 -I)4 cluster units are linked by the dithioether ligand in a 1D necklace structure. In contrast, the reaction of PhSCH2CH2SPh with CuI results in the formation of the metallopolymer [(CuI)2{,-PhS(CH2)2SPh}2]n (2). The 2D network of 2 is built from dimeric Cu2I2 units which are connected by 1,2-bis(phenylthio)ethane bridging ligands. The solid-state luminescence spectrum of 1 exhibits a strong emission around 532 nm, whereas a weak emission centred at 413 nm is observed in the case of 2. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Polymer-Supported Highly Enantioselective Catalyst for Nitro-Michael Addition: Tuning through Variation of the Number of H-Bond Donors and Spacer LengthADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009Lital Tuchman-Shukron Abstract Two series of polymer-bound bifunctional organocatalysts, based on chiral diamine scaffolds, were prepared by solid-phase synthesis. The series, incorporating a single hydrogen bond donor carbamate functionality, was notably more enantioselective in the Michael reaction of acetone and nitrostyrene than the series that includes a double hydrogen bond donor urea moiety, or the polymer-bound diamine that lacks sufficiently acidic protons. The best aminocarbamate catalyst promoted the addition of acetone to nitroolefins with enantioselectivity unmatched by known heterogeneous catalysts. Introduction of a short linear spacer between the support and the scaffold improves the activity but reduces the selectivity of the catalyst. Alternatively, an increase in the reaction yield could be induced by the benzoic acid additive. [source] Effect of the Molecular Size of Analytes on Polydiacetylene ChromismADVANCED FUNCTIONAL MATERIALS, Issue 9 2010Donghwan Seo Abstract The pH chromism of polydiacetylenes (PDAs) is examined with respect to the molecular size and acidity of acid analytes, along with the alkyl spacer length of primary-amine-functionalized diacetylene (DA) lipids. pH turns out to be an important parameter to charge amine headgroups of PDA but a change in pH does not necessarily result in a PDA color change. The molecular size of acid analytes is identified as another factor that can produce a configurational change in PDA amine headgroups, followed by perturbation of the ene,yne conjugated backbone. In addition, the length of a flexible alkyl spacer between the amine headgroup and the amide group of the diacetylene lipids is found to strongly affect the degree of PDA chromatic transition. The longer alkyl spacer shows a smaller chromatic transition from blue to red phase. The alkyl spacer seems to provide a certain degree of freedom to the amine headgroup, thus decreasing the transfer of headgroup steric effects to the PDA backbone. These correlations found for PDA chromism are applied to the development of a system that colorimetrically detects diethyl phosphate (DEP), a degraded nerve agent simulant. PDA liposomes show a selective chromatic transition upon binding with DEP compared to other acid analytes. [source] Insight into Proton Conduction of Immobilised Imidazole Systems Via Simulations and Impedance Spectroscopy,FUEL CELLS, Issue 3-4 2008W. L. Cavalcanti Abstract The proton conduction in immobilised imidazole systems has been investigated in order to support the design of new membrane materials for polymer electrolyte membrane fuel cells (PEMFC). In the experimental part of this work, proton conductivities are measured via impedance spectroscopy. The simulation and modelling are performed combining molecular dynamics simulations and energy barrier calculations; the analysis is done via the proton jump energy barrier, collision ratio and radial distribution function. The dependence of the proton mobility on the temperature, spacer length and the density of conducting groups per area is presented. Donors and acceptors groups approach to each other within a distance from 2.8 to 3,Å where the energy barrier for a proton transfer is very low, which favours the proton jump under the studied conditions. The proton conductivity increases with increase in the spacer length. The simulation results are in good agreement with the proton conductivities presented. [source] Gold Nanoparticles Stabilized by Acetylene-Functionalized Multidentate Thioether Ligands: Building Blocks for Nanoparticle SuperstructuresADVANCED FUNCTIONAL MATERIALS, Issue 21 2009Torsten Peterle Abstract Aiming at the formation of inorganic/organic hybrid gold nanoparticle superstructures, the design and synthesis of acetylene-monofunctionalized multidentate thioether ligands and their ability to stabilize gold nanoparticles are presented. Rather monodisperse gold particles with diameters of about 1,nm are obtained, which are coated by a small number of ligands, each comprising a silyl-protected acetylene. The acetylene is attached at the end of a rigid ethynylene-phenylene unit of variable length, leading to functionalized gold nanoparticles carrying acetylenes at different distances from the nanoparticle surface. These particles are interlinked by diacetylene formation and are investigated by transmission electron microscopy and UV/vis spectroscopy, revealing the formation of nanoparticle aggregates and small superstructures such as dimers or trimers while the nanoparticles themselves retain their integrity. The interparticle distance in small nanoparticle superstructures reflects the ethynylene-phenylene spacer length corroborating the wet chemical interlinking as the origin of these organic/inorganic hybrid structures. [source] Synthesis of Cyclic Peptides by Photochemical Decarboxylation of N -Phthaloyl Peptides in Aqueous SolutionHELVETICA CHIMICA ACTA, Issue 12 2002The synthesis of a variety of cyclic peptides from N -phthaloyl-protected di-, tri-, tetra-, and pentapeptides with different aminocarboxylic acid tethers by photodecarboxylation , initiated by intramolecular electron transfer , has been explored in aqueous media. The progress and the chemoselectivity of the follow-up processes after CO2 extrusion were traced by the respective pH/time-profiles, as well as by the overall change in pH after completion of the reaction. The competition between cyclization and simple oxidative decarboxylation depends on spacer length and geometry, H-bonding interaction between the electron accepting phthalimide CO groups and amide H-atoms, as well as the geometric reorganization coupled with the radical combination step and the formation of the lactam rings. With progressing reaction, hydrolysis of the phthalimide chromophore becomes an increasingly important side reaction due to the constant increase in pH. The use of phosphate-buffered aqueous media consequently improved the cyclization yields. The ground-state interactions between amide groups and the terminal COO, group with the imide CO groups were studied for the model system [N -(phthaloyl)glycyl]sarcosine (1) by NMR spectroscopy where the amide (E/Z)-equilibrium depends on the presence of carboxylate vs. free carboxylic acid, demonstrating the role of H-bonding and metal coordination. [source] Synthesis and properties of segmented main-chain liquid-crystalline polyurethanes with a high aspect ratio mesogenic diol as a chain extenderJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2002T. Padmavathy Abstract Main-chain liquid-crystalline polyurethanes were synthesized based on a high aspect ratio mesogenic diol (4-{[4-(6-hydroxyhexyloxy)-phenylimino]-methyl}-benzoic acid 4-{[4-(6-hydroxyhexyloxy)-phenylimino]-methyl}-phenyl ester) as a chain extender; polycaprolactone (PCL) diol soft segments of different number-average molecular weights (530, 1250, or 2000); and different diisocyanates, including 1,4-hexamethylene diisocyanate (HMDI), 4,4,-methylene bis(cyclohexyl isocyanate) (H12MDI), and 4,4,-methylene bis(phenyl isocyanate) (MDI). The structure of the polymers was confirmed with Fourier transform infrared spectroscopy, and differential scanning calorimetry and polarizing microscopy measurements were carried out to examine the liquid-crystalline and thermal properties of the polyurethanes, respectively. The mesogenic diol was partially replaced with 20,50 mol % PCL. A 20 mol % mesogen content was sufficient to impart a liquid crystalline property to all the polymers. The partial replacement of the mesogenic diol with PCL of various molecular weights, as well as the various diisocyanates, influenced the phase transitions and the occurrence of mesophase textures. Characteristic liquid-crystalline textures were observed when a sufficient content of the mesogenic diol was present. Depending on the flexible spacer length and the mesogenic content, grained and threadlike textures were obtained for the HMDI and H12MDI series polymers, whereas the polyurethanes prepared from MDI showed only grained textures for all the compositions. The polymers formed brittle films and could not be subjected to tensile tests. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1527,1538, 2002 [source] The effects of spacer length on the fluorescence quantum yields of the benzofurazan compounds bearing a donor,acceptor systemLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 1 2002Maki Onoda Abstract We studied the effects of spacer length on the fluorescence quantum yields (,) of photoinduced electron transfer (PET) reagents, using nitrobenzoxadiazole (NBD) derivatives that have the ,NMe2 moiety and NBD,NH, fluorophore as electron donor (D) and electron acceptor (A), respectively. The , values were reduced as the spacer length became shorter (n,,,4; n is the number of methylene units of the spacer) and the fluorescence recovered by suppression of the PET process. It is necessary for the useful PET reagents to link D and A with a short spacer to obtain a difference in the , values between fluorescent ,off-state' and ,on-state'. Copyright © 2002 John Wiley & Sons, Ltd. [source] A Polycation Scaffold Presenting Tunable "Click" Sites: Conjugation to Carbohydrate Ligands and Examination of Hepatocyte-Targeted pDNA DeliveryMACROMOLECULAR BIOSCIENCE, Issue 6 2010Chen-Chang Lee Abstract A versatile polycation scaffold that can easily be modified with targeting ligands has been designed, synthesized, and characterized. A series of galactose-containing polymers has been produced to demonstrate the ease of modification of this polynucleotide delivery vehicle motif via the click reaction and to study how various structural modifications affect recognition by ASGPr on hepatocytes. A small library of structures was created where DCS and alkyl spacer length between the targeting group and the polymer backbone was varied. The novel polymer scaffold described proves to be a valuable tool for understanding structure/activity relationships of complexes made with receptor-targeted polymers. [source] Photoluminescent behavior of poly(3-hexylthiophene) derivatives with a high azobenzene content in the side chainsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2005Xiongyan Zhao Abstract A series of polythiophene derivatives with substantially higher azobenzene contents in the side chains were prepared via copolymerization of 3-hexylthiophene with four different types of 4-((4-(phenyl)azo)phenoxy)alkyl-3-thienylacetate. The alkyl spacers with different lengths, i.e. butyl, hexyl, octyl and undecyl groups were used between the azobenzene group and the thiophene ring. The compositions, structures and thermal properties of these polythiophene derivatives were characterized. The structural dependence of photoluminescent emission, photochromic behavior of these copolymers were systematically studied and compared with poly(3-hexylthiophene). The results show that the azobenzene substitution renders the polythiophene some interesting optical properties that can be modulated by UV light irradiation. In the azobenzene modified polythiophene, the intensity of photoluminescent emission associated with the conjugated polythiophene main chain was found to decrease significantly upon UV irradiation. The finding suggests that the photo-induced trans - cis isomerization of the azobenzene pendant groups has a significant effect on photoluminescent emission, particularly when short spacers are used between azobenzene groups and the main chain. However, the effect becomes less prominent when longer spacers are used between the azobenzene group and the main chain. Furthermore, UV irradiation of the copolymers also resulted in an increase in intensity and broadening of bandwidth for the absorption peak associated with the polythiophene backbones. Again the magnitude of intensity changes upon UV irradiation were found to be dependent on the spacer length between the azobenzene group and polythiophene main chain. Copyright © 2005 John Wiley & Sons, Ltd. [source] Synthesis, characterization and properties of azobenzene side-chain polythiophene,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3-5 2003Leong Huat Gan Abstract Thiophene monomers with an azobenzene moiety of different spacer length at the 3-position of the thiophene ring were synthesized. The monomers were polymerized and copolymerized with 3-hexyl thiophene to investigate the influence of an azobenzene side-chain on the properties of polythiophene, which has been widely used as a conducting polymer and has also been found many other applications. The polymers were characterized with UV-vis, FT-IR spectrophotometry, gel permeation chromatographic (GPC) analysis, DSC, TGA, elemental analysis and X-ray diffractometry. The polymers showed novel thermochromic and photoresponsive properties in polymer solutions and solid films. It was found that an azobenzene side-chain could bring about substantial thermochromic and photochromic changes to the polythiophene backbone as compared with non-azobenzene side-chain polythiophenes. These property changes could be triggered or controlled by light or heat on the basis of azobenzene trans,cis or cis,trans isomerization. Copyright © 2003 John Wiley & Sons, Ltd. [source] Modification of pLL/DNA complexes with a multivalent hydrophilic polymer permits folate-mediated targeting in vitro and prolonged plasma circulation in vivoTHE JOURNAL OF GENE MEDICINE, Issue 5 2002Christopher M. Ward Abstract Background Gene delivery vectors based on poly(L -lysine) and DNA (pLL/DNA complexes) have limited use for targeted systemic application in vivo since they bind cells and proteins non-specifically. In this study we have attempted to form folate-targeted vectors with extended systemic circulation by surface modification of pLL/DNA complexes with hydrophilic polymers. Methods pLL/DNA complexes were stabilised by surface modification with a multivalent reactive polymer based on alternating segments of poly(ethylene glycol) and tripeptides bearing reactive ester groups. Folate moieties were incorporated into the vectors either by direct attachment of folate to the polymer or via intermediate poly(ethylene glycol) spacers of 800 and 3400,Da. Results Polymer-coated complexes show similar morphology to uncoated complexes, their zeta potential is decreased towards zero, serum protein binding is inhibited and aqueous solubility is substantially increased. Intravenous (i.v.) administration to mice of coated complexes produced extended systemic circulation, with up to 2000-fold more DNA measured in the bloodstream after 30,min compared with simple pLL/DNA complexes. In further contrast to simple pLL/DNA complexes, coated complexes do not bind blood cells in vivo. Folate receptor targeting is shown to mediate targeted association with HeLa cells in vitro, leading to increased transgene expression. We demonstrate for the first time that DNA uptake via the folate receptor is dependent on pEG spacer length, with the transgene expression relatively independent of the level of internalised DNA. Conclusions We show increased systemic circulation, decreased blood cell and protein binding, and folate-targeted transgene expression using pLL/DNA complexes surface-modified with a novel multireactive hydrophilic polymer. This work provides the basis for the development of plasma-circulating targeted vectors for in vivo applications. Copyright © 2002 John Wiley & Sons, Ltd. [source] Supported Membranes with Well-Defined Polymer Tethers,Incorporation of Cell ReceptorsCHEMPHYSCHEM, Issue 3 2004Oliver Purrucker Abstract We report the design of supported lipid membranes attached to the surface by tailored lipopolymer tethers. A series of well-defined lipopolymers were synthesized by means of living cationic polymerization of 2-methyl-2-oxazolines. The polymers were equipped with a silane coupling group on the proximal, and lipid anchors on the distal chain ends. The length of the intermediate hydrophilic polymer tether was varied (n=14, 18, 33) to change the distance between the membrane and the substrate. Supported membranes have been prepared in two-steps. First, a suitable lipopolymer/lipid mixture was deposited by Langmuir,Blodgett transfer, and annealed to establish the covalent coupling to the surface. On the dry lipopolymer/lipid monolayer, the upper leaflet was deposited by vesicle fusion. Optimization of both preparation steps resulted in the formation of stable and defect-free membranes. Impacts of the spacer length and the lipopolymer fraction upon the lateral diffusivity of the lipids were systematically compared by fluorescence recovery after photobleaching (FRAP). First experiments on the incorporation of a large transmembrane cell receptor (integrin ,IIb,3) into the polymer-tethered membrane suggested that the length of the polymer tether plays a crucial role in distribution of the proteins on the surface. [source] Anhydrous Polymeric Proton Conductors Based on Imidazole Functionalized PolysiloxaneFUEL CELLS, Issue 3-4 2006G. Scharfenberger Abstract Intrinsically proton conducting polymers with imidazole as proton solvent tethered to a polysiloxane backbone via a flexible spacer have been synthesized. Apart from the standard characterization also their thermal properties and transport behavior have been investigated. The materials exhibit proton conductivity as a consequence of self-dissociation of the imidazole moieties and "structure diffusion" of the resulting defects. In particular, no liquid phase such as water or monomeric imidazole is needed for the observed proton conductivities. To study the influence of the tether structure on the transport properties, cyclic oligomers and open chain polymers with different spacer lengths have been synthesized. The materials are thermally stable up to 200,°C and become soft around room temperature. The conductivity exhibits VTF and WLF behavior with maximum conductivities around ,,=,1.5.10,3,S,cm,1 at T,=,160,°C. The activation volume of the conductivity as derived from pressure dependent measurements is found to be unusually high. The lowest activation volumes and the highest conductivities are observed for the materials with the highest segmental mobilities, i.e. the longest spacers. Proton self-diffusion coefficients as obtained from PFG NMR diffusion measurements are significantly higher than expected from the proton conductivities obtained by dielectric spectroscopy. This corresponds to unusually high Haven ratios which have been interpreted by correlated proton transfers allowing for fast proton diffusion while minimizing the separation of ionic charge carriers. [source] Metal-Free Click Polymerization: Synthesis and Photonic Properties of Poly(aroyltriazole)sADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Anjun Qin Abstract Regioselective 1,3-dipolar polycycloadditions of tetraphenylethene (TPE)-containing diazides 1,3 and bis(aroylacetylene) 4 are initiated by simple heating, affording poly(aroyltriazole)s (PATAs) PI,PIII with high molecular weights in high yields. The PATAs are completely soluble in common organic solvents and stable at temperatures up to 358,°C. Thanks to their TPE units, the polymers show aggregation-induced emission and work as explosive sensors with high sensitivity. The PATAs are optically transparent in the whole visible spectral region. Their refractive indexes can be tuned to a great extent (,n,,,0.08) by simply changing their alkyl spacer lengths. The modified Abbé numbers of the PATAs are very high (up to 273), indicative of very low optical dispersions in the telecommunication-important wavelength region. UV irradiation through a photomask quenches the light emissions of the polymers, enabling the generation of two-dimensional fluorescent images without development. The polymers can be readily photo-crosslinked, yielding three-dimensional patterns with high resolutions. [source] Synthesis of liquid crystalline poly(1-pentyne)s and fabrication of polyacetylene,perovskite hybridsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2006Jianli Hua Abstract Poly(1-pentyne)s containing biphenyl and phthalimido pendant groups with different spacer lengths {P1(m); [HCC(CH2)3OBiphOCO(CH2)mN(CO)2C6H4]n, Biph4,4,biphenylyl; m = 7, 10} are synthesized in satisfactory yields by WCl6 -Ph4Sn catalyst in toluene at elevated temperatures. The structures and properties of the polymers are characterized and evaluated by IR, NMR, TGA, DSC, POM, and XRD analyses. Both of the polymers are thermally stable (Td , 300 °C) and exhibit nematicity at high temperatures. Their phthalimido groups are converted into amino groups by hydrolysis, which can, after acidification, complex with lead(II) bromide to furnish polyacetylene,perovskite hybrids in high yields. The organic components contribute good solubility to the hybrids, while the perovskite framework induces the polyacetylene chains to align within the inorganic sheets. The hybrids emit a strong UV light of 374 nm upon photoexcitation, whose quantum yield increases with an increase in the spacer length. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3538,3550, 2006 [source] Microstructures Based on Thermotropic Liquid-Crystalline Polymers in the Low Molar Mass Nematogenic 5CBMACROMOLECULAR SYMPOSIA, Issue 1 2005Fabiano V. Pereira Abstract Summary: The unique characteristics of two polyacrylates having the same side chain chiral mesogenics groups and different spacer lengths allowed the stabilization of ordered polymer rich-phases in solution with the nematic solvent 5CB. These microstructures are smectic having fibrous-like and rode-like morphologies, in spite of the mesophases of the polymers in bulk. The interactions between the mesogenic groups in the polymer and the solvent 5CB stabilize the microstructures and leads to birefringence at temperatures above the 5CB clearing point. Polarized optical microscopy data are complemented by SAXS to fully describe the mesomorphic behavior of the mixtures. [source] Oligosaccharide Mimics Containing Galactose and Fucose Specifically Label Tumour Cell Surfaces and Inhibit Cell Adhesion to FibronectinCHEMBIOCHEM, Issue 2 2005Evelyn Y.-L. Abstract With the aim of establishing a versatile and easy synthesis of branched saccharides for biological applications, we used molecular-dynamics simulations to model Lewisyto two classes of di- or triantennary saccharide mimetics. One set of mimetics was based on 1,3,5-tris(hydroxymethyl)cyclohexane (TMC) as the core, the other on furan, and both were derivatised with galactose and/or fucose. The TMC-based saccharides were biotinylated, while the furan disaccharides were treated with maleimide-activated biotin in a Diels,Alder fashion to yield oxazatricyclodecanes (OTDs). These were then assayed as cell-surface labels in human colon (SW480 and CaCo-2), liver (PLC), Glia (U333,CG,343) and ovary (SKOV-3) tumour cell lines. Discrete staining patterns were observed in all cells, usually at one or two poles of the cells, particularly with the asymmetric 3-,- L -fucopyranosyloxymethyl-4-,- D -galactopyranosyloxymethyl-OTD. Normal SV40-transformed fibroblasts (SV80) showed no staining. Adhesion of the highly metastatic mouse melanoma line B16,F10 to fibronectin was inhibited by 80,% by the TMC-digalactoside and by 30,% by 3,4-bis-(,- D -galactopyranosyloxymethyl)furan. None of the saccharide mimetics inhibited the adhesion of the less metastatic B16,F1 line. Migration of B16,F10 cells through MatrigelTMwas greatly inhibited by the TMC-digalactoside and weakly inhibited by the TMC-trigalactoside. The saccharide mimetics that had shown the best structural agreements with the terminal saccharides of Lewisyin the molecular dynamics simulation were also the most biologically potent compounds; this underlines the predictive nature of molecular dynamics simulations. The use of the non-saccharide cores enabled us to adapt spacer lengths and terminal saccharides to optimise the structures to bind more avidly to cell-surface lectins. [source] Efficient Preparation of Photoswitchable Dithienylethene-Linker-Conjugates by Palladium-Catalyzed Coupling Reactions of Terminal Alkynes with Thienyl Chlorides and Other Aryl HalidesCHEMISTRY - AN ASIAN JOURNAL, Issue 5 2010Marc Zastrow Abstract Three photochromic dithienylethene-linker-conjugates with an adamantane core containing different spacer lengths and footprint areas with carboxylic anchoring groups are synthesized. The synthetic routes start either from the ethynylene-linker 5 or the iodo-substituted linker 8. Reaction conditions for the final Sonogashira coupling step between ethynylene-linker 5 with the chloro-substituted dithienylethene 4 in the presence of [PdCl2(CH3CN)2]/X-Phos and Cs2CO3 or K3PO4 are optimized using 2-chloro-5-methylthiophene (9) and triethylsilylacetylene or triisopropylsilylacetylene (10,a,b) as model compounds. Experimental conditions are found to suppress the activation of the C(sp)Si bond in TIPS-acetylene 10,b, a reaction leading to a subsequent cross-coupling reaction to form by-product 12. Furthermore, activation of the C(sp)Si bond in the presence of the fluorinated backbone of the chloro-substituted dithienylethene 4 can also be prevented. The photochromic properties of the conjugate 3 and its precursor dithienylethene 7,b are also investigated. Beschrieben wird die Synthese von drei photochromen Dithienylethen-Linker-Konjugaten, bestehend aus einer zentralen Adamantaneinheit, Carbonsäure-Ankergruppen, sowie variierenden "Spacerlängen" und unterschiedlichen Fußabdrücken. Die synthetischen Routen zu diesen Verbindungen beginnen entweder ausgehend von dem Ethinylen-Linker 5 oder von dem Iod-substituierten Linker 8. Für die finale Sonogashira-Kupplung wurden dabei Reaktionsbedingungen zwischen dem Ethinylen-Linker 5 und dem Chlor-substituierten Dithienylethen 4 in Gegenwart von [PdCl2(CH3CN)2]/X-Phos und Cs2CO3 oder K3PO4 verwendet, die anhand von Modellstudien mit 2-Chlor-5-methylthiophen (9) und Triethylsilylacetylen oder Triisopropylsilylacetylen (10,a,b) optimiert wurden. Dabei wurden experimentelle Bedingungen gefunden, um die Aktivierung der C(sp)-Si-Bindung von TIPS-Acetylen 10,b zu unterdrücken, welche ansonsten zu dem Nebenprodukt 12 führte. Darüber hinaus konnte die Aktivierung der C(sp)-Si-Bindung in Anwesenheit des fluorierten Rückgrats des chlor-substituierten Dithienylethen 4 verhindert werden. Schließlich wurden die photochromen Eigenschaften des Konjugates 3 und der Vorläuferverbindung 7,b untersucht. [source] | |||||||||||||