Oligo(fluorenyleneethynylenegermylene)s and their metallopolymers

Oligo(fluorenyleneethynylenegermylene)s and their polyplatinynes are synthesized and photophysically characterized; inclusion of heavy germylene bridges greatly boosts the phosphorescence decay rate in metallopolymers.     

Au36(SPh)23 nanomolecules

A new core size protected completely by an aromatic thiol, Au(36)(SPh)(23), is synthesized and characterized by MALDI-TOF mass spectrometry and UV-visible spectroscopy. The synthesis involving core size changes is studied by MS, and the complete ligand coverage by aromatic thiol group is shown by NMR.     

Oligo(p-phenyleneethynylene)s with hydrogen-bonded coplanar conformation

A series of monodispersed oligo( p-phenyleneethynylene)s were synthesized bearing intramolecular hydrogen bonds between side chains of adjacent phenylene units in the backbone. Thus, all repeating units of the molecules are constrained in a coplanar orientation. Such planarized conformation is considered favorable for single-molecule conductance. Photophysical characterization results show narrowed bandgaps and extended conjugation lengths, consistent with a rigid, planar backbone framework as a result of intramolecular hydrogen bonding.     

Stereocontrolled Synthesis of Oligo(nucleoside phosphorothioate)s

Encouraging results obtained for modulation of gene expression by antisense oligonucleotides and their analogues have kindled hopes for a new generation of therapeutics against viral infections, cancer, and many other diseases. Among such analogues, oligo(nucleoside phosphorothioate)s (Oligo-S) have generally shown the highest efficacy in inhibiting the biosynthesis of “unwanted” proteins. The first clinical trials of antisense agents are now in progress using Oligo-S against genital warts and acute myeloid leukemia, and tests of Oligo-S against AIDS should follow soon. Nevertheless, their mechanism of action, internalization, cellular trafficking, subcellular localization, and interaction with cellular proteins is still poorly understood. It is assumed a priori that application involves rapid and efficient molecular recognition of target RNA by Oligo-S; however, the effects of the chirality of Oligo-S have so far been unappreciated, because Oligo-S has not yet been synthesized with stereocontrol. Indeed, the diastereomeric composition of Oligo-S has never been determined, primarily because of the lack of appropriate analytical methods. Since each of the diastereomers is a stereochemically unique chemical entity, questions arise as to which diastereomer is responsible for an observed biological response, including positive (curative) or possibly negative (toxic) side effects. In this review we intend provide a perhaps somewhat speculative assessment of the problems associated with the stereo-controlled synthesis of Oligo-S and to discuss the state-of-the-art in this field including strategies that may lead to Oligo-S of predetermined chirality. This article is not intended to discourage researchers from further studies of dia-steromeric mixtures of Oligo-S as potential pharmaceuticals. Throughout the history of medicinal chemistry numerous useful medicines were discovered, developed, and employed without the detailed knowledge of their structure. Indeed, the composition of the vaccines discovered by Pasteur is a subject of vigorous study still today.     

Dramatically Enhanced Fluorescence of Heteroaromatic Chromophores upon Insertion as Spacers into Oligo(triacetylene)s

In continuation of a previous study on the modulation of π‐electron conjugation of oligo(triacetylene)s by insertion of central hetero‐spacer fragments between two (E)‐hex‐3‐ene‐1,5‐diyne ((E)‐1,2‐diethynylethene, DEE) moieties (Fig. 1), a new series of trimeric hybrid oligomers ( 14 – 18 and 22 – 24 , Fig. 2) were prepared (Schemes 1–3). Spacers used were both electron‐deficient (quinoxaline‐based heterocycles, pyridazine) and electron‐rich (2,2′‐bithiophene, 9,9‐dioctyl‐9H‐fluorene) chromophores. With 19–21 (Scheme 4), a series of transition metal complexes was synthesized as potential precursors for nanoscale scaffolding based on both covalent acetylenic coupling and supramolecular assembly. The UV/VIS spectra (Fig. 3) revealed that the majority of spacers provided hetero‐trimers featuring extended π‐electron delocalization. The new hybrid chromophores show a dramatically enhanced fluorescence compared with the DEE dimer 13 and homo‐trimer 12 (Fig. 5). This increase in emission intensity appears as a general feature of these systems: even if the spacer molecule is non‐fluorescent, the corresponding hetero‐trimer may show a strong emission (Table 2). The redox properties of the new hybrid chromophores were determined by cyclic voltammetry (CV) and rotating‐disk voltammetry (RDV) (Table 3 and Fig. 5). In each case, the first one‐electron reduction step in the hetero‐trimers appeared anodically shifted compared with DEE dimer 13 and homo‐trimer 12 . With larger spacer chromophore extending into two dimensions (as in 14 – 18 , Fig. 2), the anodic shift (by 240–490 mV, Table 3) seems to originate from inductive effects of the two strongly electron‐accepting DEE substituents rather than from extended π‐electron conjugation along the oligomeric backbone, as had previously been observed for DEE‐substituted porphyrins.     

含二茂铁齐聚苯乙炔分子导线的合成

通过二碘代二茂铁与不同炔化物进行Sonogashira偶联反应,合成了3种新颖的含有二茂铁单元的苯乙炔齐聚物,用1H NMR、13C NMR和MS测试技术分别对其结构进行了表征。 并借助量子化学计算对3种分子的电子结构进行了预测,结果显示,该类型分子导线具有不同于其它类型苯乙炔齐聚物的LUMO能级持续衰减特征,因此极有可能具备极为优良的电子传输性能。     

Oligo(nucleoside Phosphorothioate)s: The Quest of P-Chirality

The influence of the sense of chirality at phosphorus of internucleotide phosphorothioate groups in oligo(nucleoside phosphorothioate)s is discussed in terms of stability of stereodefined PS-Oligos in the intra- and intercellular media and newly discovered exclusive ability of R P -PS-Oligos containing homopurine tracts towards the formation of triple-stranded species of one phosphorothioate and two complementary RNA strands stechiometry.     

Carbon‐bridged Oligo(phenylenevinylene)s as Light‐harvesting Antenna for Porphyrins

The efficacy of carbon‐bridged oligo(phenylenevinylenes)s (COPVs) as light‐harvesting antenna for porphyrins is demonstrated using a series of 5,15‐di‐COPVn‐substituted free‐base and zinc porphyrins, COPVn‐MP‐COPVn (n=1–3, M=H₂, Zn). These molecules were synthesized by Suzuki–Miyaura cross‐coupling reactions of COPVn‐Bpin and Br‐H₂P‐Br . The absorption spectra of these compounds in solution show a significant expansion of the Soret band region together with a bathochromic shift of the Q band, suggesting a significant interaction between these chromophores in the ground state. The photoluminescence quantum yield of the porphyrin‐COPV conjugates is enhanced up to four times relative to the parent porphyrins. Theoretical calculations also indicated interactions between these chromophores in the HOMO, which suggests that the light‐harvesting ability stems from the expansion of the π‐electron‐conjugation system.     

Bridge-Length-Dependent Intramolecular Charge Transfer in Bis(dianisylamino)-Terminated Oligo(p-phenylene)s

Radical cations of bis(dianisylamino)-terminated oligo(p-phenylene)s (OPPs) with up to five phenyl moieties were characterized by means of UV/Vis-NIR and variable-temperature ESR spectroscopy to investigate the bridge-length-dependence on intramolecular charge/spin self-exchange between two nitrogen redox-active centers. Additionally, a comparative study between bis(dianisylamine)-based mixed-valence (MV) radical cations connected by p-terphenylene and hexa-peri-hexabenzocoronene (HBC) π-bridging units also provided information on the influence of extended π-conjugation over the OPP-bridge due to the planarization between adjacent phenylene units on the strength of electronic coupling. The present study on a homologous series of organic MV systems clarifies the attenuation factor through the OPP-bridge and the linear relationship between the electrochemical potential splitting and the electronic coupling in the region of intermediate-to-weak electronic coupling regime.     

Efficacy of End-Only-Functionalized Oligo(arylene-ethynylene)s in Killing Bacterial Biofilms

Cationic end-only-functionalized oligo(arylene-ethynylene)s (EO-OPEs) have recently been found to be broad-spectrum and effective antimicrobial agents because of their unique structure and optical properties. In this study, we investigated their potential use for preventing and reducing Escherichia coli (E. coli) biofilms. The Calgary biofilm device (CBD) was used to form bacterial biofilms of E. coli; in these studies, the minimum inhibitory concentration (MIC) and the minimum biofilm eradication concentration (MBEC) were determined. E. coli biofilms uniformly grow on pegs of the CBD device lid. The MIC values determined for EO-OPEs are comparable to those found for standard antibiotics such as kanamycin (MIC = 11.2 μg/mL). About 10-30 times the concentration of EO-OPEs was required to eradicate E. coli biofilms and prevent regrowth in the dark. Near-UV irradiation of EO-OPEs enhanced their efficacy in killing biofilms.     

Oligo(ethylene glycol) containing polymer brushes as bioselective surfaces

The nitroxide-mediated polymerization of styrenic monomers containing oligo(ethylene glycol) (OEGn) moieties was chosen for the preparation of biocompatible polymer brushes tethered to silicon oxide surfaces due to the broad range of monomer structures available and the use of a nonmetallic initiator. These surfaces were characterized by near-edge X-ray absorption fine structure and water contact angle measurements. The biocompatibility of these grown polymer brushes was studied and compared with deposited assemblies of surface-bound OEGn-terminated silanes with selected chain lengths. Grown polymer brushes with short OEGn side chains suppressed protein adsorption significantly more than the deposited assemblies of short OEGn chains, and this was attributed to higher surface coverage by the brushes. Cell adhesion studies confirmed that OEGn-containing polymer brushes are particularly effective in preventing nonspecific adhesion. Studies of protein adsorption and cell localization carried out with specific ligands on surfaces patterned demonstrated the potential of these surface-tethered polymer brushes for the formation of micro- and nanoscale devices.     

Platinum(II) Schiff base as versatile phosphorescent core component in conjugated oligo(phenylene-ethynylene)s

Novel phosphorescent conjugated oligo(phenylene-ethynylene)s featuring a central tunable platinum(II) Schiff base signalling unit with promising photophysical properties have been investigated to pave their development towards polymeric congeners for sensing applications.     

Oligo(glycerol) Methacrylate Macromonomers

Linear, protected ω‐methoxy oligo(glycerol) methacrylate (OGly^PMA) macromonomers are synthesized via anionic ring‐opening polymerization of ethoxyethyl glycidyl ether (EEGE) followed by termination with methacrylic acid anhydride ( = 3–11, PDI < 1.30). The covalently bound methacrylate moiety allows the homopolymerization of OGly^PMA as well as copolymerization with low molecular weight comonomers. In homopolymerizations, macromonomers are polymerized by atom transfer radical polymerization (ATRP) yielding well‐defined graft polymers ( = 20 000–30 000 g mol⁻¹). Acidic hydrolysis of the protecting groups releases water‐soluble polyhydroxy‐functional structures. First results on the copolymerization with 2‐hydroxyethyl methacrylate (HEMA) are given in the final part of this work.     

Oligo (p -phenylene)s substituted with long alkoxy chains I. Thermotropic liquid crystalline properties and UV absorption/emission characteristics

A series of linear oligo (p-phenylene)s containing three, five and seven phenylene groups, modified with short lateral and long terminal alkoxy chains, were synthesized via Palladium complex-catalysed cross-coupling reactions. The thermotropic liquid crystalline and UV absorption/emission properties of these compounds were studied. It was observed that tri (p -phenylene)s develop a rich mesomorphism including tilted smectic type mesophases (SmC and SmF/SmI) and the nematic phase, whereas penta- and hepta-(p-phenylene)s substituted with short lateral chains develop only the nematic phase. From these observations it is clear that the short lateral chains hinder the layered molecular packing typical of smectic phases and promote the formation of the less ordered liquid-like nematic phase. Mesophases appeared at lower temperatures when longer end chains were used. The optical properties studied by UV-Vis and emission spectroscopy indicate that these systems are promising candidates for blue-emitting layers in electroluminescent devices.     

Oligo ( p -phenylene)s substituted with long alkoxy chains I. Thermotropic liquid crystalline properties and UV absorption/emission characteristics

A series of linear oligo ( p -phenylene)s containing three, five and seven phenylene groups, modified with short lateral and long terminal alkoxy chains, were synthesized via Palladium complex-catalysed cross-coupling reactions. The thermotropic liquid crystalline and UV absorption/emission properties of these compounds were studied. It was observed that tri ( p -phenylene)s develop a rich mesomorphism including tilted smectic type mesophases (SmC and SmF/SmI) and the nematic phase, whereas penta- and hepta-( p -phenylene)s substituted with short lateral chains develop only the nematic phase. From these observations it is clear that the short lateral chains hinder the layered molecular packing typical of smectic phases and promote the formation of the less ordered liquid-like nematic phase. Mesophases appeared at lower temperatures when longer end chains were used. The optical properties studied by UV-Vis and emission spectroscopy indicate that these systems are promising candidates for blue-emitting layers in electroluminescent devices.     

Oligo(p-phenylene-ethynylene)s with backbone conformation controlled by competitive intramolecular hydrogen bonds

A series of conjugated oligo(p-phenylene-ethynylene) (OPE) molecules with backbone conformations (that is, the relative orientations of the contained phenylene units) controlled by competitive intramolecular hydrogen bonds to be either co-planar or random were synthesised and studied. In these oligomers, carboxylate and amido substituents were attached to alternate phenylene units in the OPE backbone. These functional groups were able to form intramolecular hydrogen bonds between neighbouring phenylene units. Thereby, all phenylene units in the backbone were confined in a co-planar conformation. This planarised structure featured a more extended effective conjugation length than that of regular OPEs with phenylene units adopting random orientation due to a low rotational-energy barrier. However, if a tri(ethylene glycol) (Tg) side chain was appended to the amido group, it enabled another type of intramolecular hydrogen bond, formed by the Tg chain folding back and the contained ether oxygen atom competing with the ester carbonyl group as the hydrogen-bond acceptor. The outcome of this competition was proven to depend on the length of the alkylene linker joining the ether oxygen atom to the amido group. Specifically, if the Tg chain folded back to form a five-membered cyclic structure, this hydrogen-bonding motif was sufficiently robust to overrule the hydrogen bonds between adjacent phenylene units. Consequently, the oligomers assumed non-planar conformations. However, if the side chain formed a six-membered ring by hydrogen bonding with the amido NH group, such a motif was much less stable and yielded in the competition with the ester carbonyl group from the adjacent phenylene unit. Thus, the hydrogen bonds between the phenylene units remained, and the co-planar conformation was manifested. In our system, the hydrogen bonds formed by the back-folded Tg chain and amido NH group relied on a single oxygen atom as the hydrogen-bond acceptor. The additional oxygen atoms in the Tg chain made a negligible contribution. A bifurcated hydrogen-bond motif was unimportant. From our results, in combination with the results from an independent study by Meijer et al., it is evident that intramolecular hydrogen bonds involving back-folded oligo(ethylene glycol) moieties may differ in their structural details. Absorption spectroscopy served as a convenient yet sensitive technique for analysing hydrogen-bonding motifs in our study.     

Synthesis and characterization of polymethacrylates containing conjugated oligo(phenylene ethynylene)s as side chains

In order to form suitable systems designed for resonance energy transfer, a series of monodisperse methacrylate‐based monomers containing rigid π‐conjugated oligo(phenylene ethynylenes) with different sizes of the conjugated systems ( M1 – M3 ), and therefore different optoelectronic properties, were synthesized and subsequently polymerized using the reversible addition–fragmentation chain transfer polymerization technique ( P1 – P3 ). In addition, these oligomers were also copolymerized with methyl methacrylate. The obtained polymers were characterized by ¹H NMR spectroscopy, size exclusion chromatography, and analytical ultracentrifugation. The photophysical properties of the polymers were studied by UV–vis absorption and emission spectroscopy in diluted solutions as well as in thin films and compared to the photophysics of the corresponding monomers. Thereby, changes going from monomeric to polymeric systems could be detected in fluorescence quantum yields and lifetimes pointing to energy trapping, e.g., energy transfer. Donor–acceptor copolymers containing different numbers of monomeric units within the side chain exhibit differences in the emission spectra, indicating that energy trapping in polymers is very sensitive to structural properties such as the chain length. UV–vis absorption spectroscopy as well as time‐resolved lifetime studies indicate intrapolymer and interpolymer energy transfer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Solid‐Phase Synthesis of Oligo(triacetylene)s and Oligo(phenylenetriacetylene)s Employing Sonogashira and Cadiot?Chodkiewicz‐Type Cross‐Coupling Reactions

We describe the first polymer‐supported synthesis of poly(triacetylene)‐derived monodisperse oligomers, utilizing Pd⁰‐catalyzed Sonogashira and Cadiot? Chodkiewicz‐type cross‐couplings as the key steps in the construction of the acetylenic scaffolds. For our investigations, Merrifield resin functionalized with a 1‐(4‐iodoaryl)triazene linker was chosen as the polymeric support ( R2 ; Figure and Scheme 3). The linker selection was made based on the results of several model studies in the liquid phase (Schemes 1 and 2). For the solid‐support synthesis of the oligo(phenylene triacetylene)s 7b – 7d , a set of only three reactions was required: i) Pd⁰‐catalyzed Sonogashira cross‐coupling, ii) Me₃Si? alkyne deprotection by protodesilylation, and iii) cleavage of the linker with liberation of the generated oligomers (Scheme 5). The longest‐wavelength absorption maxima of the oligo(phenylene triacetylene)s 7a – 7d shift bathochromically with increasing oligomeric length, from λ_max 337 nm (monomer 7a ) to 384 nm (tetramer 7d ; Table 2). Based on the electronic absorption data, the effective conjugation length (ECL) of the oligo(phenylene triacetylene)s is estimated to involve at least four monomer units and 40 C‐atoms. π‐Electron conjugation in these oligomers is less efficient than in the known oligo(triacetylene)s 14a – 14d (Table 2) due to poor transmittance of π‐electron delocalization by the phenyl rings inserted into the oligomeric backbone. Similar conclusions were drawn from the electrochemical properties of the two oligomeric series as determined by cyclic (CV) and rotating‐disk voltammetry (RDV; Table 3). In sharp contrast to 14b – 14d , the oligo(phenylene triacetylene)s 7b – 7d are strongly fluorescent, with the highest quantum yield Φ_F=0.69 measured for trimer 7c (Table 2). Whereas the Sonogashira cross‐coupling on solid support proceeded smoothly, optimal conditions for alkyne? alkyne cross‐coupling reactions employing Pd⁰‐catalyzed Cadiot? Chodkiewicz conditions still remain to be developed, despite extensive experimentation (Scheme 7 and Table 1).