Acetylene Spacer Research Articles

Low-bandgap thiophene dendrimers for improved light harvesting

This article follows our previous work on the synthesis and characterization of pi-conjugated dendrimers for use in organic solar cells. Here we discuss five new thiophene-based dendrimers that were synthesized in order to study the relationship between their chemical structures and electronic properties. Three of these dendrimers incorporate acetylene spacers, included to relieve steric strain, between the thiophene arms and phenyl cores used in previous studies. Only a small effect on the electronic properties is observed upon inclusion of the acetylene spacer in the three-arm dendrimer, 3G1-2S-Ac. In contrast, a decrease in the bandgap is observed for the four-arm dendrimer, 4G1-2S-Ac, due to a reduction of interactions between the arms in the more sterically congested 1,2,4,5-arrangement around the phenyl core, resulting in delocalization of the exciton through the phenyl core. Incorporation of electron-withdrawing cyano groups on the phenyl core of the three-arm dendrimer, 3G1-2S-CN, resulted in a very large (∼0.5 eV) decrease in the bandgap, due to stabilization of the lowest unoccupied molecular orbital, and the low energy absorption band in this material is attributed to a transition with significant intramolecular charge-transfer character. The electronic properties of three- and four-arm dendrimers with electron-donating dibutylaniline moieties attached to the end of the thiophene dendron, 3G1-2S-N and 4G1-2S-N respectively, are almost identical, indicating that they are dominated by the arms, with no through-core communication allowed, even for the para-linked arms of 4G1-2S-N. However, there is a significant increase in the molar absorptivity of these materials, concomitant with significant broadening of the absorption spectrum, which is an important attribute in light-harvesting applications.

Conjugated anthracene derivatives as donor materials for bulk heterojunction solar cells: olefinic versus acetylenic spacers

Substituting olefinic for acetylenic pi-spacers in anthracene-based conjugated semiconductor donors leads to appreciable increases in the power conversion efficiencies of the resulting bulk heterojunction solar cells.

X-ray structures of quinone dimers linked either directly or through acetylene spacers

X-ray structures of quinone dimers linked either directly or through acetylene spacers

Thiolated Nucleotides for Immobilisation of DNA Oligomers on Gold Surfaces

contradictory results for the conduction behaviour of DNA. [9] Some of these contradictions could be attributed to influences of the DNA sequence or the environment of the molecules. On the other hand, it is evident that poor overlap of the orbitals of the thiols with the p-system of the DNA as well as unreliable or unspecific bonding of the thiols to the metal electrodes are most likely playing a major role in causing these contradictions. Along these lines we became interested in the synthesis of oligonucleotides that bear short thioalkyl functions in close proximity to the p-system of the nucleobase to facilitate electrical transport through dsDNA. [10] Herein we report the synthesis of new thiolated nucleotides, their incorporation in DNA oligonucleotides as well as studies employing fluorescence and atomic-force microscopy for verifying the immobilisation of the thiolated species onto gold substrates. For the design of the thiol modified nucleosides, future applications for transport measurements are kept in mind. The 5-position of thymidine was chosen for modification to be in close proximity to the p-system and to maintain accessibility over the major groove in double strand DNA, thus 1 shown in Scheme 1 bears a thiol-moiety directly attached to the nucleobase that is protected as ether. In another approach thymidine 2 is synthesised via the introduction of a thiophene moiety conjugated via an alkyne spacer to the nucleobase. To commence the synthesis of 1, the protected 5-iodo-2’-deoxyuridine 3 [11] was first treated with NaH and after cooling to 788C with nBuLi and 1,2-bis(2-(trimethylsilyl)ethyl) disulfane

New Push‐Pull Chromophores Featuring TCAQ (11,11,12,12‐Tetracyano‐ 9,10‐anthraquinodimethane) and Other Dicyanovinyl Acceptors

AbstractStable, highly colored push‐pull chromophores with NMe2 donor and C=C(CN)2 acceptor moieties, featuring intense intramolecular charge‐transfer (CT) bands in the UV/Vis spectra, are reported. In an attempt to prepare the quinoid push‐pull systems 2, chromophores 10 and 11, with a central cyclohexene spacer, were obtained and characterized by X‐ray analysis. A series of donor‐substituted TCAQ (11,11,12,12‐tetracyano‐9,10‐anthraquinodimethane) derivatives were synthesized, using the Knoevenagel condensation between appropriately functionalized anthraquinones and malononitrile, mediated by the Lehnert reagent (TiCl4/pyridine), as the key step. HCl addition to triple bonds was observed when this transformation was applied to alkynylated anthraquinones. Electrochemical studies by cyclic voltammetry (CV) and rotating‐disk voltammetry (RDV) showed that introduction of donor substituents into the TCAQ core of 25, 26, and 31 shifts the first reduction potential to more negative values, while chromophores bearing guanidine moieties (27, 28) displayed a specific and complex redox behavior. Both electrochemical and UV/Vis data provide good evidence that D–A conjugation is more efficient through olefinic (in 10) than through acetylenic (in 37) spacers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Ferrocenylethynyl Derivatives of Nucleoside Triphosphates: Synthesis, Incorporation, Electrochemistry, and Bioanalytical Applications

Modified dATP (2'-deoxyadenosine-5'-triphosphate) and dUTP (2'-deoxyuridine-5'-triphosphate) bearing ferrocene (Fc) labels linked via a conjugate acetylene spacer were prepared by single-step aqueous-phase cross-coupling reactions of 7-iodo-7-deaza-dATP or 5-iodo-dUTP with ethynylferrocene. The Fc-labeled dNTPs were good substrates for DNA polymerases and were efficiently incorporated to DNA by primer extension (PEX). Electrochemical analysis of the 2'-deoxyribonucleoside triphosphates (dNTPs) and PEX products revealed significant differences in redox potentials of the Fc label bound either to U or to 7-deazaA and between isolated dNTPs and conjugates incorporated to DNA. Prospective bioanalytical applications are outlined.

First hyperpolarizabilities of transition metal sesquifulvalene complexes

The static first hyperpolarizabilities of some typical transition metal sesquifulvalene complexes have been assessed within the framework of the density functional theory (DFT). The molecular orbital analyses illuminate that the molecular structural factors predominate the characteristics of frontier molecular orbitals, linear electronic absorption spectra and static first hyperpolarizabilities, in a great extent. The complexations of sesquifulvalene derivatives (C 5H 4–π-bridge–C 7H 6) with the (η 5-C 5H 5)Fe +–, (η 5-C 5H 5)Ru +– and (CO) 3Mn +– monocations gain mononuclear ferrocenyl complexes and result in longer distances and larger charge separations between the electronic donor and acceptor, and narrower HOMO–LUMO gaps. These changes in return enhance the electric dipole moment and static electric first hyperpolarizability. Nevertheless, the subsequent integrations of mononuclear ferrocenyl sesquifulvalene monocations with the (CO) 3Cr– group reduce static first hyperpolarizability for the complexes with the ethylene or acetylene spacer but increase static first hyperpolarizability for the complexes with the benzene bridge. Additionally, the complexations of mononuclear ferrocenyl sesquifulvalene monocations with the (η 5-C 5H 5)Ru +– monocation result in the considerable reducement of static first hyperpolarizability. These differences have been well interpreted in terms of an integration of molecular geometry with electronic structure.

Structural implications of ring shape, dimension, and metal atom insertion in nanosized cyclic oligothiophenes: Joint Raman and density functional theory study

This paper reports on a combined spectroscopic and density functional theory study on a series of cyclo(diacetylenes-oligothiophenes) with different shapes and dimensions. The case of a macrocycle fragmented by the insertion of Pt metallic atoms is illustrated as well. The analysis covers the neutral and oxidized samples. A full assignment of the spectra has been proposed, supported by BP86/cc-pVDZ theoretical calculations. Ring shape and molecular dimension have been related with the C[Double Bond]CC-C structural parameters and Raman wave numbers. Platinum atom insertion within the acetylene spacer seems to soften ring strain owing to the rupture of the strained circular shape. Oxidation causes an overall downshift of the Raman wave numbers likely due to the skeletal relaxation of CC conjugated path, while the ring shape of each macrocycle is conserved upon oxidation.

Tuning the Thermotropic and Lyotropic Properties of Liquid‐Crystalline Terpyridine Ligands

A rational synthetic strategy is developed to provide compact and simple terpyridine (terpy) mesogens that show liquid-crystallinity both as pure compounds and in organic solution (amphotropic compound). The use of a central 4-methyl-3,5-diacylaminophenyl platform equipped with two lateral aromatic rings, each bearing three appended aliphatic chains, allows connection of a 2,2':6',2''-terpyridine fragment through a polar group such as an ester, amide, or flat conjugated alkyne linker. For the T(12)ester and T(12)amide scaffolds, the mesophase is best described as a lamellar phase, in which the molecules self-assemble into columnar stacks held together in layers. In the T(12)amide case, the additional amide link results in significant stabilization of the lamellar phase. The driving forces for the appearance of columnar ordering are the hydrogen-bonding interactions of the amide groups, which induce head-to-tail pi-stacking of the terpy subunits. Replacing the polar linker by a nonpolarized but linear alkyne spacer, as in the T(12)ethynyl compound, provides a columnar mesophase organized in a rectangular lattice of p2gg symmetry. In this arrangement, two nondiscotic molecules arranged into dimers by hydrogen bonding and pi-pi stacking pile up in a head-to-tail manner to form columns. In addition, the T(12)amide compound proves to be an excellent gelator of cyclohexane, linear alkanes, and DMSO. The resulting robust and transparent gels are birefringent and formed by large aggregates that are readily aligned by shear-flow. TEM and freeze-fracture microscopy reveal that the gels have an original layered morphology made of fibers.

Synthesis and Biological Evaluation of 6-(Alkyn-1-yl)furo[2,3-d]pyrimidin-2(3H)-one Base and Nucleoside Derivatives

Derivatives of the 2'-deoxynucleoside of furo[2,3-d]pyrimidin-2(3H)-one with long-chain alkyl (or 4-alkylphenyl) substituents at C6 exhibit remarkable anti-VZV (varicella-zoster virus) potency and selectivity, and analogous 2',3'-dideoxynucleoside derivatives show anti-HCMV (human cytomegalovirus) activity. We now report a synthetic approach that enables the preparation of long-chain 6-(alkyn-1-yl)furo[2,3-d]pyrimidin-2(3H)-ones in which the rodlike acetylene spacer replaces the 4-substituted-phenyl ring at C6. Analogues with methyl, beta-d-ribofuranosyl, beta-d-arabinofuranosyl, and 2-deoxy-beta-d-erythro-pentofuranosyl substituents at N3 have been prepared. Long-chain derivatives at C6 in the 2'-deoxynucleoside series showed virus-encoded nucleoside kinase-sensitive anti-VZV activity. Surprisingly, 3-methyl-6-(octyn-1-yl)furo[2,3-d]pyrimidin-2(3H)-one (prepared as a negative anti-VZV test control) exhibited anti-HCMV activity, which supports the possibility of development of non-nucleoside anti-HCMV agents originating from uncomplicated derivatives of such bicyclic ring systems.

Phenyls with a Twist

CHEMISTRY Planar arrays of fused aromatic rings are stabilized by electron delocalization in their extended π-network, which leads to the bright colors that make these molecules such useful dyes. However, chemists interested in the competing interplay of steric and electronic factors have long tried to coax such molecules out of planarity by appending bulky substituents. Dai et al. have managed to crowd four pendant phenyls along a 10-carbon stretch of a diindenophenanthrene framework. The compound was formed in 20% yield from a precursor with four alkyne spacers, which were fused into the heptacyclic core through a series of intramolecular rearrangements. Crystallography revealed a severely twisted, nonplanar core geometry, particularly in the central phenanthrene ring. The dangling phenyl substituents are stacked parallel to one another in a partial helix, with the outer phenyls oriented 184° apart, presumably the result of both steric and π-stacking interactions. Nuclear magnetic resonance spectroscopy revealed a rotational barrier of ∼14 kcal/mol for the outer phenyls and a higher barrier for the two rings between them. — JSY Org. Lett. 10.1021/ol0481434 (2004).

Solution‐Phase Microwave‐Assisted Synthesis of Unsubstituted and Modified α‐Quinque‐ and Sexithiophenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Solution-phase microwave-assisted synthesis of unsubstituted and modified alpha-quinque- and sexithiophenes.

The facile synthesis of poorly soluble unsubstituted and modified alpha-quinque- and sexithiophenes under microwave irradiation in the liquid phase is described. The use of microwave irradiation allowed these compounds to be prepared in a few minutes and at high yields by means of the Suzuki cross-coupling reaction. Unsubstituted sexithiophene was obtained in 10 min via the one-pot borylation/Suzuki reaction, purified according to a very simple procedure, and isolated in 84% yield. The efficient synthesis of two new methylated quinque- and sexithiophenes displaying liquid crystalline properties is reported. A new microwave-assisted methodology for the conversion of aldehyde-terminated quinque- and sexithiophenes into the corresponding cyano derivatives is also described. The use of microwaves was extended to the Sonogashira coupling reaction and found to be very effective in the preparation of a quinquethiophene containing acetylenic spacers. The electronic and optical characterization of this compound is reported and discussed in relation to that of unsubstituted quinquethiophene.

Cation sensors containing a (bpy)Re(CO)3 group linked to an azacrown ether via an alkenyl or alkynyl spacer: synthesis, characterisation, and complexation with metal cations in solution.

Two [(bpy)Re(CO)3L]+ complexes (bpy = 2,2'-bipyridine), where L contains an aza-15-crown-5 ether which is linked to Re via an alkenyl- or alkynyl-pyridine spacer, have been synthesised along with model complexes. Solutions of the complexes in acetonitrile have been studied by UV-Vis absorption spectroscopy, and by 1D and 2D 1H NMR spectroscopy. Strong UV-Vis bands, assigned to intraligand charge-transfer transitions localised at the L ligands, blue shift on protonation of the azacrown nitrogen atom or on complexation of alkali-metal (Li+, Na+ and K+) or alkaline-earth metal (Mg2+, Ca2+ and Ba2+) cations to the azacrown; the magnitude of the blue shift is dependent on the cation, with protonation giving the largest shift of ca. 100 nm. Cation binding constants in the range of log K= 1-4 depend strongly on the identity of the metal cation. Protonation or cation complexation causes downfield shifts in the 1H NMR resonances from most of the azacrown and L ligand protons, and their magnitudes correlate with those of the blue shifts in the UV-Vis bands; shifts in the azacrown 1H NMR resonances report on how the different metal cations interact with the macrocycle. UV-Vis and 1H NMR spectra of the free L ligands enable the effect of the Re centre to be assessed. Together, the data indicate that the alkene spacer gives a more responsive sensor than the alkyne spacer by providing stronger electronic communication across the L ligand.

Donor strength of π-extended tetrathiafulvalenes: ionisation energies vs. oxidation potentials. A joint theoretical and experimental study

The π-donor strength of extended tetrathiafulvalenes (TTFs) has been investigated as a function of the electronic character and length of the spacer between the two dithiole rings. First and second ionisation energies were calculated with B3LYP/6-311++G(2d,p)//B3LYP/6-31+G(d) and B3LYP/6-311++G(2d,p)//PM3 computational methods and correlated with the number of carbon atoms in the spacer. Theoretical IEs are compared to electrochemical oxidation potentials Eoxs to elucidate the importance of solvation. There are remarkable differences between spacers comprised of sp2 and sp carbon atoms. Thus, Eox increases with IE for alkene spacers whereas there is no clear correlation for alkyne spacers, which is ascribed to a solvent effect. Calculations using a continuum solvent model support this interpretation. Moreover, we report the synthesis of a new alkyne-extended TTF that contains six triple bonds in the spacer. Its redox properties were investigated and discussed in context of the calculations. Finally, the donor strength of an alkyne-extended TTF, bis(1,3-dithiol-2-ylidene)hexa-2,4-diyne, was evaluated by its ability to form an inclusion complex with the cyclic acceptor cyclobis(paraquat-p-phenylene).

Novel Extended Tetrathiafulvalenes Based on Acetylenic Spacers: Synthesis and Electronic Properties.

ChemInformVolume 33, Issue 48 p. 127-127 Heterocyclic Compounds Novel Extended Tetrathiafulvalenes Based on Acetylenic Spacers: Synthesis and Electronic Properties. Francois Diederich, Francois Diederich Lab. Org. Chem., ETH-Hoenggerberg, CH-8093 Zuerich, Switz.Search for more papers by this authoret al. et al., et al. et al. Lab. Org. Chem., ETH-Hoenggerberg, CH-8093 Zuerich, Switz.Search for more papers by this author Francois Diederich, Francois Diederich Lab. Org. Chem., ETH-Hoenggerberg, CH-8093 Zuerich, Switz.Search for more papers by this authoret al. et al., et al. et al. Lab. Org. Chem., ETH-Hoenggerberg, CH-8093 Zuerich, Switz.Search for more papers by this author First published: 18 May 2010 https://doi.org/10.1002/chin.200248127Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume33, Issue48December 3, 2002Pages 127-127 RelatedInformation

Novel estradiol derivatives labeled with Ru, W, and Co complexes. Influence on hormone-receptor affinity of several organometallic groups at the 17 alpha position.

In order to elucidate the extent to which recognition of the estrogen receptor is influenced by addition of an organometallic substituent at the 17 alpha position, modification of 17 beta-estradiol at this position was carried out by using the organometallic groups -C identical to C(eta 5-C5H4)RuCp, CH2-(eta 5-C5H4)RuCp, -C identical to C-(eta 5-C5H4)-W(CO)3(Me), -(C identical to CCHO)Co2(CO)6, and -(C identical to CCH2OH)Co2(CO)6. The relative binding affinity (RBA) values for estradiol receptor alpha showed that recognition was good (RBA between 20 and 13.5%) when the organometallic moiety was attached at the end of a rigid alkyne spacer. However, the affinity of the modified hormone for the receptor was severely reduced (RBA = 1%) for a substituent such as -CH2-(eta 5-C5H4)RuCP, in which the spacer is reduced to a single flexible sp3 carbon atom, allowing the organometallic moiety greater freedom of movement around the attachment point. The RBA values found were in agreement with results obtained from a molecular-modeling study in which 5, an organometallic hormone with a rigid spacer, or 7, a molecule with a flexible spacer, was inserted into the cavity of the recently characterized Ligand-Binding Domain of estrogen receptor alpha.

Novel extended tetrathiafulvalenes based on acetylenic spacers: synthesis and electronic properties.

A selection of mono- and diacetylenic dithiafulvalenes was synthesized and employed for the construction of extended tetrathiafulvalenes (TTFs) with hexa-2,4-diyne-1,6-diylidene or deca-2,4,6,8-tetrayne-1,10-diylidene spacers between the two 1,3-dithiole rings. By stepwise acetylenic scaffolding using (E)-1,2-diethynylethene (DEE) building blocks, an extended TTF containing a total of 18 C(sp) and C(sp(2)) atoms in the spacer was prepared. The versatility of the acetylenic dithiafulvene modules was also established by the efficient synthesis of a thiophene-spaced TTF, employing a palladium-catalyzed cross-coupling reaction. The developed synthetic protocols allow functionalization of the extended TTFs in three general ways: with 1) peripheral substituents on the fulvalene cores, 2) alkynyl moieties laterally appended to the spacer, and 3) cobalt clusters involving acetylenic moieties. Strong chromophoric properties of the extended TTFs were revealed by linear and nonlinear optical spectroscopies. Extensive electrochemical studies and calculations on these compounds are also reported, as well as X-ray crystallographic analyses.

Gemini Surfactants with Acetylenic Spacers

A total of 24 dicationic geminis surfactants were synthesized, having a 2-butynyl spacer and chain lengths varying from 8 to 18 carbons. Geminis with more flexible butyl spacers were also synthesiz...

Acceleration of Photoinduced Charge Separation in Porphyrin-C60 Dyad with an Acetylene Spacer

Abstract A porphyrin-C60 dyad with an acetylene spacer has been synthesized for the first time. The rate constant for charge separation in the dyad is larger by a factor of about three compared with a porphyrin-C60 dyad with an amide spacer, showing that the triple bond is a good electron transfer mediator.