Alkane Side Chains Research Articles

Controlling Optoelectronic Behavior in Poly(fluorene) Networks Using Thiol–Ene Photo-Click Chemistry

Thiol–ene photo-click chemistry is used to cross-link poly(fluorene) derivatives incorporating varying length alkene side-chains into conjugated thin film networks with tunable network architecture, offering a systematic handle on network architecture in cross-linked conjugated polymers. Newly reported poly(fluorene)s with 5- and 11-carbon length thiol–ene compatible side-chains are cross-linked using difunctional and tetra-functional thiol cross-linkers to afford networks of varying connectivity which are tracked by FTIR, contact profilometry, and photo calorimetry. Fluorenone “defects” are additionally incorporated into the poly(fluorene) networks and act as a uniquely effective colorimetric indicator of electronic communication within the conjugated network. This provides a novel method for the systematic investigation of the effects of network architecture on cross-linked conjugated polymer films, which opens the door for controlling the optoelectronic properties of organic semiconductor networks as demonstrated by electroluminescent devices with improved efficiency.

Polyethylene Surface Modification by Side Chain Crystalline Block Copolymer

SummaryRecently, we found that Side Chain Crystalline Block Co‐Polymer (SCCBC), which has a long alkane side chain (>C10), can be used as a good dispersant for a concentrated polyethylene fine‐particle dispersion. We also found that the viscosity of this concentrated dispersion increased at high temperature and returned to normal at low temperature. We named this fluid Thermal Rheological Fluid (TR Fluid). The mechanism of this phenomenon involves the attachment and detachment of SCCBC. With the use of this mechanism, we examined whether it could be possible to modify the properties of a polyethylene (PE) surface. A PE film was dipped in a dilute SCCBC solution, and its surface was coated by SCCBC. The water contact angle changed from around 90° before coating to around 70° after coating. Thus, the surface of PE was made more hydrophilic. The adhesion strength was examined by a tensile test. The PE film elongated before the attached region broke. These results showed that SCCBC has a very high adhesion strength and can be used as a surface modifier or primer for attachment. Additionally, SCCBC could be easily removed from the PE film by hot water, and thus, it should be very easy to recycle or re‐use the PE.

Diffusion Wavelet Decomposition for Coarse-Graining of Polymer Chains

ABSTRACTHere we present an alternative approach to coarse graining, based on the multiresolution diffusion-wavelet approach to operator compression, which does not require explicit atomistic-to-coarse-grained mappings. Our diffusion-wavelet method takes as input the topology and sparsity of the molecular bonding structure of a system, and returns as output a hierarchical set of degrees of freedom (DoFs) of system-specific coarse-grained variables. Importantly, the hierarchical compression provides a clear framework for modeling at many model scales (levels), beyond the common two-level CG representation. Our results show that the resulting hierarchy separates localized modes, such as a single C-C vibrational mode, from larger-scale motions, e.g., long-range concerted backbone vibrational modes. Our approach correctly captures small-scale chemical features, such as cellulose ring structures, and alkane side chains or CH2 units, as well as large-scale features of the backbone. In particular, the new method’s finest-scale modes describe DoFs similar to united atom models and other chemically-defined CG models. Modes at coarser levels describe increasingly large connected portions of the target polymers. For polyethylene and polystyrene, spatial coordinates and their associated forces were compressed by up to two orders of magnitude. The compression in forces is of particular interest as this allows larger timesteps as well as reducing the number of DoFs.

Exo-Methylene-BEDT-TTF and alkene-functionalised BEDT-TTF derivatives: synthesis and radical cation salts

The syntheses of novel BEDT-TTF donors with either an exo-alkene group or a terminal alkene side chain are described along with the crystal structures of their first radical cation salts which include a new semiconductor.

Succinate esters: odd-even effects in melting points.

Dialkyl succinates show a pattern of alternating behavior in their melting points, as the number of C atoms in the alkane side chain increases, unlike in the dialkyl oxalates [Joseph et al. (2011). Acta Cryst. B67, 525-534]. Dialkyl succinates with odd numbers of C atoms in the alkyl side chain show higher melting points than the immediately adjacent analogues with even numbers. The crystal structures and their molecular packing have been analyzed for a series of dialkyl succinates with 1-4 C atoms in the alkyl side chain. The energy difference (ΔE) between the optimized and observed molecular conformations, density, Kitaigorodskii packing index (KPI) and C-H...O interactions are considered to rationalize this behavior. In contrast to the dialkyl oxalates where a larger number of moderately strong C-H...O interactions were characteristic of oxalates with elevated melting points, here the molecular packing and the density play a major role in raising the melting point. On moving from oxalate to succinate esters the introduction of the C2 spacer adds two activated H atoms to the asymmetric unit, resulting in the formation of stronger C-H...O hydrogen bonds in all succinates. As a result the crystallinity of long-chain alkyl substituted esters improves enormously in the presence of hydrogen bonds from activated donors.

Comparisons of Halogenated β-Nitrostyrenes as Antimicrobial Agents

The influence of three types of halogen-substituted E-β-methyl-β-nitrostyrenes (such as Compounds B, D, H) to overcome bacterial activity that is currently a significant health threat was studied. The evaluations of their bio-potency was measured and related to their structure and activity relationships for the purposes of serving to inhibit and overcoming resistant microorganisms. In particular, fluorine-containing β-nitrostyrenes were found to be highly active antimicrobial agents. The addition of the β-bromo group enhanced the antibacterial activity significantly. Our work has illustrated that halogen substituents at both the 4-position in the aromatic ring and also at the β-position on the alkene side chain of nitropropenyl arenes enhanced the antimicrobial activity of these compounds.

Unraveling the interplay of backbone rigidity and electron rich side-chains on electron transfer in peptides: the realization of tunable molecular wires.

Electrochemical studies are reported on a series of peptides constrained into either a 310-helix (1–6) or β-strand (7–9) conformation, with variable numbers of electron rich alkene containing side chains. Peptides (1 and 2) and (7 and 8) are further constrained into these geometries with a suitable side chain tether introduced by ring closing metathesis (RCM). Peptides 1, 4 and 5, each containing a single alkene side chain reveal a direct link between backbone rigidity and electron transfer, in isolation from any effects due to the electronic properties of the electron rich side-chains. Further studies on the linear peptides 3–6 confirm the ability of the alkene to facilitate electron transfer through the peptide. A comparison of the electrochemical data for the unsaturated tethered peptides (1 and 7) and saturated tethered peptides (2 and 8) reveals an interplay between backbone rigidity and effects arising from the electron rich alkene side-chains on electron transfer. Theoretical calculations on β-strand models analogous to 7, 8 and 9 provide further insights into the relative roles of backbone rigidity and electron rich side-chains on intramolecular electron transfer. Furthermore, electron population analysis confirms the role of the alkene as a “stepping stone” for electron transfer. These findings provide a new approach for fine-tuning the electronic properties of peptides by controlling backbone rigidity, and through the inclusion of electron rich side-chains. This allows for manipulation of energy barriers and hence conductance in peptides, a crucial step in the design and fabrication of molecular-based electronic devices.

Minimal Tags for Rapid Dual‐Color Live‐Cell Labeling and Super‐Resolution Microscopy

The growing demands of advanced fluorescence and super-resolution microscopy benefit from the development of small and highly photostable fluorescent probes. Techniques developed to expand the genetic code permit the residue-specific encoding of unnatural amino acids (UAAs) armed with novel clickable chemical handles into proteins in living cells. Here we present the design of new UAAs bearing strained alkene side chains that have improved biocompatibility and stability for the attachment of tetrazine-functionalized organic dyes by the inverse-electron-demand Diels-Alder cycloaddition (SPIEDAC). Furthermore, we fine-tuned the SPIEDAC click reaction to obtain an orthogonal variant for rapid protein labeling which we termed selectivity enhanced (se) SPIEDAC. seSPIEDAC and SPIEDAC were combined for the rapid labeling of live mammalian cells with two different fluorescent probes. We demonstrate the strength of our method by visualizing insulin receptors (IRs) and virus-like particles (VLPs) with dual-color super-resolution microscopy.

Ozonolysis of surface-adsorbed methoxyphenols: kinetics of aromatic ring cleavage vs. alkene side-chain oxidation

Abstract. Lignin pyrolysis products, which include a variety of substituted methoxyphenols, constitute a major component of organics released by biomass combustion, and may play a central role in the formation of atmospheric brown carbon. Understanding the atmospheric fate of these compounds upon exposure to trace gases is therefore critical to predicting the chemical and physical properties of biomass burning aerosol. We used diffuse reflectance infrared spectroscopy to monitor the heterogeneous ozonolysis of 4-propylguaiacol, eugenol, and isoeugenol adsorbed on NaCl and α-Al2O3 substrates. Adsorption of gaseous methoxyphenols onto these substrates produced near-monolayer surface concentrations of 3 × 1018 molecules m−2. The subsequent dark heterogeneous ozonolysis of adsorbed 4-propylguaiacol cleaved the aromatic ring between the methoxy and phenol groups with the product conclusively identified by GC-MS and 1H-NMR. Kinetic analysis of eugenol and isoeugenol dark ozonolysis also suggested the formation of ring-cleaved products, although ozonolysis of the unsaturated substituent groups forming carboxylic acids and aldehydes was an order of magnitude faster. Average uptake coefficients for NaCl-adsorbed methoxyphenols were γ = 2.3 (± 0.8) × 10−7 and 2 (± 1) × 10−6 for ozonolysis of the aromatic ring and the unsaturated side chain, respectively, and reactions on α-Al2O3 were approximately two times slower. UV–visible radiation (λ > 300 nm) enhanced eugenol ozonolysis of the aromatic ring by a factor of 4(± 1) but had no effect on ozonolysis of the alkene side chain.

Research on the Relationship between Changes of Active Groups and Gaseous Products in Different Temperatures

This paper reveals the relationship between the changes of active functional groups in coal and gaseous products. Intelligent coal heating and oxidation trial furnace and GC-4085 series gas chromatograph are used for heating and gas analyzing, then use Fourier-transform infrared spectrophotometer instrument (FTIR) tests the reactive functional groups of coal under different temperatures. Analyzing result shows that: alkane side chains of aliphatic react in the whole process of heating and oxidation. -CH2-, -CH2-CH2- and other bridged linkages crack into free radical groups when they are heated. CO, CO2 and alkane gases are formed in the reaction. At about 110°C, ethane gas appears; stretching vibration of aromatics, carbonyl acid in the plane and unsaturated hydrocarbon key in aromatic hydrocarbon are relatively stable, which start to react after 140°C with very small amounts of ethylene and propylene gases produced. CO, CO2 and alkane gases, which are produced by the reaction that peripheral side chains of coal adsorb surface complexes and the gases break away from the coal, are important parts for CO, CO2 and alkane, etc. to generate in low temperature.

Convenient Detection of Pd(II) by a Metal–Organic Framework with Sulfur and Olefin Functions

A highly specific, distinct color change in the crystals of a metal-organic framework with pendant allyl thioether units in response to Pd species was discovered. The color change (from light yellow to orange/brick red) can be triggered by Pd species at concentrations of a few parts per million and points to the potential use of these crystals in colorimetric detection and quantification of Pd(II) ions. The swift color change is likely due to the combined effects of the multiple functions built into the porous framework: the carboxyl groups for bonding with Zn(II) ions to assemble the host network and the thioether and alkene functions for effective uptake of the Pd(II) analytes (e.g., via the alkene-Pd interaction). The resultant loading of Pd (and other noble metal) species into the porous solid also offers rich potential for catalysis applications, and the alkene side chains are amenable to wide-ranging chemical transformations (e.g., bromination and polymerization), enabling further functionalization of the porous networks.

Ring‐Rearrangement Metathesis of Nitroso Diels–Alder Cycloadducts

Strained nitroso Diels-Alder bicyclo[2.2.1] or [2.2.2] adducts functionalized with alkene side chains of diverse length undergo a ring-rearrangement metathesis process with external alkenes and Grubbs II or Hoveyda-Grubbs II ruthenium catalysts, under microwave irradiation or classical heating, to deliver cis-fused bicycles of various ring sizes, which contain a N-O bond. These scaffolds are of synthetic relevance for the generation of molecular diversity and to the total synthesis of alkaloids. The observation of unexpected reactions, such as epimerization or one-carbon homologation of the alkene side chain, is also reported.

Polydiacetylene Incorporated with Peptide Receptors for the Detection of Trinitrotoluene Explosives

Because of their unique optical and stimuli-response properties, polydiacetylene-based platforms have been explored as an alternative to complex mechanical and electrical sensing systems. We linked chromic responsive polydiacetylene (PDA) onto a peptide-based molecular recognition element for trinitrotoluene (TNT) molecules in order to provide a system capable of responding to the presence of a TNT target. We first identified the trimer peptide receptor that could induce chromic changes on a PDA backbone. We then investigated the multivalent interactions between TNT and our peptide-based receptor by nuclear magnetic resonance (NMR) spectroscopy. We further characterized various parameters that affected the conjugated PDA system and hence the chromic response, including the size of end-group motifs, the surface density of receptors, and the length of alkane side chains. Taking these necessary design parameters into account, we demonstrated a modular system capable of transducing small-molecule TNT binding into a detectable signal. Our conjugated PDA-based sensor coupled with molecular recognition elements has already proven useful recently in the development of another sensitive and selective electronic sensor, though we expect that our results will also be valuable in the design of colorimetric sensors for small-molecule detection.

Polymer solar cells based on diphenylmethanofullerenes with reduced sidechain length

Diphenylmethanofullerenes (DPMs) show interesting properties as acceptors in polymer bulk heterojunction solar cells due to the high open circuit voltages they generate compared to their energy levels. Here we investigate the effect of reducing the alkane sidechain length of the DPMs from C12 to C6 in the properties of the solar cell. This change leads to an increase in the electron mobility, thus allowing for a lower fullerene content, which in turn results in an increase in the short circuit current and, finally, in an increase in the efficiency of the device (from 2.3 to 2.6%) due to the higher concentration of the more absorbing polymer in the film. Atomic force microscopy images and external quantum efficiencies suggest the absence of crystallization of the fullerene to be at the origin of the slightly reduced performance of DPMs versus the standard fullerene [6,6]-phenyl-C61-butyric acid methyl ester, implying that higher efficiencies could be possible with this class of fullerenes.

ChemInform Abstract: Photochemistry of Alkenyl- and Acetal-Substituted Pyridines.

Ethyl 3-(2-pyridyl)propionate formation results from irradiation of 3-(2-pyridyl)propanal diethylacetal in acetonitrile. This photoreaction is unique to the heteroaromatic pyridine and only occurs in acetonitrile. A minor product, 1-aza-2-methyl-3-(2-ethanal diethylacetal)-4-ethoxycycloocta-1,3,5,7-tetraene, is also obtained. The irradiation of 2-methyl-6-(2-pyridyl)-2-pentene in the presence of various sensitizers results in addition to the alkene side-chain to produce oxetanes.

ChemInform Abstract: Tandem Photocyclization-Intramolecular Addition Reactions of Aryl Vinyl Sulfides. Observation of a Novel (2 + 2)Cycloaddition-Allylic Sulfide Rearrangement.

Photocyclization of aryl vinyl sulfides reportedly proceeds via thiocarbonyl ylide intermediates. The photochemical behavior of several aryl vinyl sulfides, which incorporate a pendant alkene side chain, was explored. In general, naphthyl and phenyl vinyl thioethers provided product which are consistent with photocyclization to a thiocarbonyl ylide intermediate followed by either intramolecular hydrogen shift or subsequent intramolecular ylide-alkene addition. Product distribution is influenced by solvent and temperature effect

Vibrational Spectroscopic Studies of Cocrystals and Salts. 3. Cocrystal Products Formed by Benzenecarboxylic Acids and Their Sodium Salts

X-ray powder diffraction, differential scanning calorimetry, infrared absorption spectroscopy, and Raman spectroscopy have been used to study the phenomenon of salt formation in four benzenecarboxylic acids (benzoic acid, phenylacetic acid, hydrocinnamic acid, and 4-phenylbutanoic acid), and in the 1:1 stoichiometric products formed by the cocrystallization of a free acid and a sodium salt. Assignments were derived for the observed peaks in both infrared absorption and Raman spectra of the reactants and their products. In all instances, it was observed that the energy of the antisymmetric stretching mode of the carbonyl group of the free benzenecarboxylic acid invariably shifted to higher energies when that acid formed a cocrystal with a sodium salt of another benzenecarboxylic acid. In addition, the symmetric stretching mode of the benzenecarboxylic acid carbonyl group disappeared in the Raman spectrum of its sodium salt and was also absent in the Raman spectrum of the cocrystal product. It was also found that the antisymmetric carboxylate anion stretching mode, the symmetric carboxylate anion stretching mode, the out-of-plane carboxylate deformation mode, and the vibrational modes associated with the phenyl ring and alkane side chains were not useful spectroscopic tools to differentiate cocrystal and sodium salt, as the observed differences of these vibrational modes did not exhibit significantly consistent differences between the various forms.

Copolymer-Derived Nanotubes

The synthesis of organic nanotube structures with well-defined dimensions is described. Multicomponent bottlebrush copolymers 5 are synthesized, which adopt a cylindrical shape. The alkene side chains are cross-linked via cross-metathesis, and the internal polylactide core is degraded to generate hollow nanotubes. Water-soluble nanotubes can also be generated by varying the nature of the polymeric precursors.

Importance of Side Chains and Backbone Length in Defect Modeling of Poly(3-alkylthiophenes)

Geometric defects in conjugated polymers play a critical role in determining electronic structure and properties such as charge carrier mobility and band gap. Because the relative roles of individual defects are experimentally difficult to discern, computational approaches provide valuable insight if appropriate molecular models are used. Poly(3-alkylthiophenes) are often modeled with very short backbones and without their side chains. We demonstrate the shortcomings of this approach for modeling torsional disorder in poly(3-hexylthiophene) (P3HT). Using a hybrid density functional model, we identify a minimal acceptable model to comprise approximately 10 monomers with explicitly treated alkane side chains. Potential applications of this work extend to polymer electronics and optoelectronics.

Thin Film Microstructure of a Solution Processable Pyrene-Based Organic Semiconductor

Semiconducting 6,7,15,16-tetrakis(dodecylthio)quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]phenazine (TQPP-12) has been synthesized as a candidate solution-processable semiconductor for organic electronics applications. We characterize the microstructure of TQPP-12 in films using a combination of polarized photon absorption spectroscopies (X-ray, vis, and infrared), X-ray diffraction, and scanning probe techniques. This characterization strategy allowed for the determination of molecular orientation and packing style within thin films of this complex molecule. The TQPP-12 molecules are arranged within layers, and the aromatic cores are separated from the alkane side chains. Both the core long axes and side chains are highly tilted with respect to surface normal, and the conjugated planes of the core are cofacially packed.