Methoxy Side Groups Research Articles

Linear oligo(phenylenevinylene)-based covalent organic frameworks.

Covalent organic frameworks (COFs) incorporating oligo(phenylenevinylene) units have shown promise in enhancing photocatalytic hydrogen evolution. This study presents a series of linear oligo(phenylenevinylene)-based COFs with various ratios of β-ketoenamine to imine linkages. The COFs-950-OMe are crystalline, exhibiting higher surface area compared to amorphous COFs-950, due to the introduction of methoxy side groups.

In situ formation of fatty acid methyl esters via thermally assisted methylation by lignin during torrefaction of oil palm biomass

Torrefaction of oil palm empty fruit bunch (EFB) biomass was performed at six temperatures between 210 and 360 °C. The composition of the evolved and trapped condensates was analyzed by GC/MS and the torrefied biomass samples were characterized by pyrolysis-GC/MS (Py-GC/MS). The analyses showed that the thermal treatment of the biomass produced significant amounts of fatty acid methyl esters (FAMEs). The in situ FAME formation was explained by the reaction of the lipid and lignin contents of the biomass; i.e., the fatty acid moieties of triglycerides were methylated by the methoxy side groups of lignin during the thermal treatment. The reaction was verified by the pyrolysis of a model mixture, using Py-GC/MS and thermogravimetry/mass spectrometry, which consisted of the EFB lipid extract and an isolated beech wood lignin. Demethylation of lignin resulted changes in its thermal decomposition; smaller amounts of 4-methylguaiacol and 4-methylsyringol were evolved and the char yield was increased. The GC/MS analysis of the EFB condensates showed that FAME conversion was the highest and the sources of fatty acid moieties were depleted if the torrefaction temperature had been set at and above 330 °C. The free fatty acid content of EFB was relatively high, which evaporated at lower temperatures before the rate of FAME formation increased between 270 and 300 °C. In comparison with torrefaction, only a small portion of FAMEs formed during the flash pyrolysis of raw EFB at 450 °C indicating that the prolonged heating of the oily biomass favors the FAME formation. Pyrolysis-GC/MS measurements of the torrefied samples showed that the triglyceride residue could also be utilized if the torrefaction as pretreatment was performed at or below 300 °C. In addition, torrefaction increased the accessibility of the biomass components for FAME formation. Some other fatty acid derivatives (i.e., ketone, hydrocarbon, amide, and nitrile) were also detected in smaller amounts. The phenomenon of in situ FAME formation during pyrolysis might be a useful process to enhance pyrolytic biomass utilization by producing FAMEs as additional fuel products and increasing the char yield simultaneously.

Effect of Protonation on Optical and Electrochemical Properties of Thiophene–Phenylene-Based Schiff Bases with Alkoxy Side Groups

Three polyazomethines and their corresponding model compounds were protonated with trifluoroacetic acid, and its effect on their optical (UV–vis absorption and photoluminescence) properties and electrochemical behavior has been studied, in the context of the presence and elongation of alkoxy side groups. Moreover, the effect of environment dielectric constants (i.e., polarity of the solvent) was considered on the doping process. It has been proven that the presence of alkoxy side groups is necessary for protonation to occur, while unsubstituted compounds undergo hydrolysis to constitutive units. Acid doping of imines consisting of alkoxy side chains has resulted in a distinct bathochromic shift (>200 nm) of the low-energy absorption band. Even the length of alkyl chains has not affected the position of shifted bands; it has been observed that azomethines with smaller, methoxy side groups undergo the protonation process much faster than their octyloxy-substituted analogues, due to the absence of steric hindrance. The electrochemical studies of these alkoxy-substituted imines have indicated a better p-type behavior after protonation induced by the capability of the protonated form to easily oxidize in acetonitrile and to generate the native molecules. The environmental polarity has also had impact on the doping process, which took place only in low-polar media.

Effect of Methoxy Side Groups on the Crystal Structures of a Series of Syndiotactic Polymethoxystyrenes as Studied by the X-ray Diffraction Data Analysis

The crystal structures have been elucidated for a series of novel syndiotactic polymethoxystyrenes (OMe-SPSs) having −OCH3 groups at the ortho-, meta-, or para-positions of phenyl rings on the basi...

Methoxy-Functionalized Glycerol-Based Aliphatic Polycarbonate: Organocatalytic Synthesis, Blood Compatibility, and Hydrolytic Property.

Polymers that are biocompatible and degradable are desired for tissue engineering approaches in the treatment of vascular diseases, especially for those involving small-diameter blood vessels. Herein, we report the compatibility of a newly developed glycerol-based aliphatic polycarbonate possessing simple methoxy side groups, named poly(5-methoxy-1,3-dioxan-2-one) (PMDO), with blood cells and plasma proteins as well as its susceptibility to hydrolysis. As a consequence of the organocatalytic ring-opening polymerization (ROP) of a methoxy-functionalized cyclic carbonate derived from glycerol, PMDO with a sufficiently high molecular weight (Mn 14 kg/mol) and a narrow distribution (D̵M 1.12) was obtained for evaluation as a bulk biomaterial. This study demonstrates for the first time the organocatalytic ROP of a glycerol-based cyclic carbonate in a controlled manner. Compared with the clinically applied aliphatic polycarbonate poly(trimethylene carbonate) (PTMC), PMDO inhibits platelet adhesion by 33% and denaturation of fibrinogen by 23%. Although the wettability of PMDO based on water contact angle was almost comparable to those of PTMC and poly(ethylene terephthalate), the reason for the inhibited platelet adhesion and protein denaturation appeared to be related to the presence of specific hydrated water formed in the hydrated polymer. The improved hydration of PMDO also enhanced the susceptibility to hydrolysis, with PMDO demonstrating a slightly higher hydrolytic property than PTMC. This simple glycerol-based aliphatic polycarbonate has the following benefits: bio-based characteristics of glycerol and improved blood compatibility and hydrolytic biodegradability stemming from moderate hydration of the methoxy side groups.

Spectroscopic and electrochemical properties of thiophene-phenylene based Shiff-bases with alkoxy side groups, towards photovoltaic applications

The influence of presence and elongation of alkoxy side chains in the π-conjugated Schiff-bases has been considered on the basis of UV–Vis absorption and photoluminescence spectra of model compounds and polymers solutions in chloroform and binary solvents of different polarity. The results of these investigations have been supported by electrochemical data. It has been demonstrated that introduction of electron donating methoxy side groups decreases the energy gap, however the elongation of alkyl chains only slightly affects the electronic structure of model compounds. In the case of polymers, such octyloxy side chains improves the solubility, enabling formation of longer polymer chains, with the enhanced effective π-conjugation length and narrower energy gap, however the intensity of emission band clearly decreased. Positive solvatochromism has been observed in both absorbance and photoluminescence spectra for all investigated compounds. As the concluding task, bulk-heterojunction (BHJ) photovoltaic (PV) structures, consisting of polyazomethines blended with the fullerene derivative, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have been prepared and tested in the context of potential application in solar cells. All investigated polymers have shown the photovoltaic effect, but the best power conversion efficiency and other PV parameters have been obtained for polyazomthine with octyloxy side chains.

Synthesis and spectral properties of Methyl-Phenyl pyrazoloquinoxaline fluorescence emitters: Experiment and DFT/TDDFT calculations

Paper reports the synthesis and spectroscopic studies of two novel 1-Methyl-3-phenyl-1H-pyrazolo[3,4-b]quinoxaline (PQX) derivatives with 6-substituted methyl (MeMPPQX) or methoxy (MeOMPPQX) side groups. The optical absorption and fluorescence emission spectra are recorded in solvents of different polarity. Steady state and time-resolved spectroscopy provide photophysical characterization of MeMPPQX and MeOMPPQX dyes as materials for potential luminescence or electroluminescence applications. Measured optical absorption and fluorescence emission spectra are compared with quantum-chemical DFT/TDDFT calculations using long-range corrected xc-functionals, LRC-BLYP and CAM-B3LYP in combination with self-consistent reaction field model based on linear response (LR), state specific (SS) or corrected linear response (CLR) solvations. Performances of relevant theoretical models and approaches are compared. The reparameterized LRC-BLYP functional (ω = 0.231 Bohr−1) in combination with CLR solvation provides most accurate prediction of both excitation and emission energies. The MeMPPQX and MeOMPPQX dyes represent efficient fluorescence emitters in blue-green region of the visible spectra.

On the spectral properties of methyl and methoxy derivatives of 1,3-diphenyl-1H-pyrazolo[3,4-b]quinoxalines: Experiment and DFT/TDDFT calculations

Paper reports the synthesis and spectroscopic studies of two novel 1,3-diphenyl pyrazoloquinoxaline (PQX) derivatives with 6-substituted methyl (MePQX) or methoxy (MeOPQX) side groups. The optical absorption and fluorescence emission spectra are recorded in solvents of different polarity. Other photophysical constants, such as the fluorescence lifetime and quantum yield, radiationless and radiative rate constants, electronic transition dipole moments, give complete characterization of MePQX and MeOPQX dyes as materials for potential luminescence or electroluminescence applications. Measured optical absorption and fluorescence emission spectra are compared with the results of quantum-chemical analysis using density functional theory (DFT/TDDFT) methods based on hybrid and long range corrected (LRC) exchange-correlation (xc) functionals in combination with solvation self consistent reaction field model. Comparing to conventional hybrid xc-functionals, the DFT/TDDFT calculations using LRC xc-functionals yield considerably more accurate description of optical absorption and fluorescence emission spectra. The best description of the absorption-emission circle provides the model assuming that optical absorption takes place from preferably flat or weakly twisted molecular conformations in the ground state, as particularly is suggested by the geometrical DFT optimization, whereas the fluorescence emission would be expected from more twisted molecular conformations in the excited state.

Investigation into the ring-substituted polyanilines and their application for the detection and adsorption of sulfur dioxide

It has been demonstrated in this study that the substituents on the monomer aniline benzene ring are able to introduce the significant differences to the resulting polyaniline tm)s collective properties. We systematically evaluated the structural perturbation effects of two substituents (methyl and methoxy) of aniline monomer through the electrochemical method. Our results showed that the methoxy group induces the less structural perturbation than the methyl counterpart, because of its partial double bond restriction. The morphologies are different for the polyaniline and the ring-substituted polyanilines, in which substituted polyanilines feature the larger porosities with the addition of these side groups. The influential effects of the methoxy side group have been further illustrated and amplified by its superior sensing performance towards the environmentally-significant sulfur dioxide gas, evaluated through the construction of the quartz crystal microbalance (QCM)-based gas sensor with these polyaniline materials. The as-constructed gas sensor tm)s sensitivity, selectivity and stability in terms of its SO2 responses have been evaluated in details. The methoxy-substituted polyaniline was tested to show the unique gas sensing properties for the sulfur dioxide at the low concentrations (50•250ppm) and function as the adsorbing material at the high concentrations (500•1250ppm). Thus it can be used both as sensing material as well as a novel filter and/or storage reservoir for the removal of sulfur dioxide pollutant from the environments.

The influence of methoxy side groups and halogen nature on the mesomorphic and optical properties of symmetrical azomethines

ABSTRACTThe preparation, characterisation, thermotropic and optical properties of low-molecular azomethines with or without methoxy side group are described in this paper. The azomethine compounds were synthesised by condensation reaction of o-dianisidine/benzidine with para-halogen substituted benzaldehyde. Their properties were analysed by differential scanning calorimetry, thermogravimetry analysis, polarised optical microscopy, X-ray diffraction and optical spectroscopy. The azomethines present liquid crystalline behaviour with large mesophase range and high thermal stability. The compounds without lateral methoxy groups showed smectic A phase, while those with methoxy groups exhibited only nematic phase. The effect of methoxy group and different terminal substituents on the mesomorphic behaviour, molecular and optical properties was estimated in terms of parameters such as molecular polarisability, dipole moment, interdigitation parameter and axial ratio.

Perfluoroalkylated linear polyglycerols and their supramolecular assemblies in aqueous solution

In this study, amphiphiles composed of linear polyglycerols (LPGs) with hydroxyl, methoxy, and ethoxy side groups and end capped with one or two perfluorooctyl chains (Rf8) have been designed to form supramolecular architectures.

Influence of side groups on the performance of infrared absorbing aza‐BODIPY organic solar cells

AbstractAbstractauthoren Organic solar cells are a promising technology for a large area conversion of sunlight into electricity. In particular for solar cells based on oligomers (small molecules), efficient donor materials absorbing wavelengths larger than 780 nm are still rare. Here, we investigate three aza‐BODIPY dyes absorbing in the infrared. The addition of side groups leads to a red shift of the optical gap from 802 to 818 nm. In optimized devices using these donors in a bulk heterojunction with , we observe a higher charge carrier mobility and a higher power conversion efficiency for the molecules without a methyl or methoxy side group lowering the molecular reorganization energy. Surprisingly, the donor–acceptor blend with the lowest energy loss during the electron transfer to the yields the highest short circuit current. With increasing size of the attached side chain, the devices exhibit a larger trap density, measured by impedance spectroscopy. Based on the investigation of different blend ratios, we conclude that these traps are mainly present in the donor phase.

Free-standing, roll-able, and transparent silicone polymer film prepared by using nanoparticles as cross-linking agents

A free-standing, roll-able, and transparent silicone-based polymer film with a tensile modulus of ca. 7.8MPa and strain at the break point of 0.76% was successfully prepared by reaction between a reactive silicone oligomer with methyl- and methoxy-side groups and hydrophilic SiO2 nanoparticles. First, SiO2 nanoparticles were grafted with silicone chains by a controlled wet chemical sol–gel-type reaction with the reactive oligomers. The solvent of the resulting solution was evaporated to form a viscous suspension, casted into a film, and finally heat-treated at 100°C and 150°C. A hydrolysis and condensation reaction among silicone-grafted SiO2 nanoparticles and free silicone oligomers in the final heat treatment resulted to produce free-standing, roll-able, and transparent silicone-based polymer film. The fact that the silicone film cannot be synthesized without the presence of SiO2 nanoparticles suggests that these nanoparticles act as cross-linking agents of silicone components providing the improved mechanical properties to the composite film. The rate-controlled mixing and heating of the SiO2 aqueous/alcohol suspension and the silicone oligomer/alcohol solution was found to be the key step in the synthesis of the free-standing transparent film. While rapid addition/mixing resulted in a fragile and opaque film, a transparent material was achieved when those solutions were slowly mixed. The effect of the synthesis process on the macroscopic and microscopic properties of the prepared films is discussed along with their formation mechanism.

ChemInform Abstract: Theoretical Study of Torsion Potentials in trans-Stilbene and Substituted trans-Stilbenes: Modeling Torsions in Poly(paraphenylene vinylene) and Derivatives

We present ab initio and semiempirical quantum‐chemical calculations as well as simple molecular mechanics calculations on the gas‐phase torsion potentials of 1,1’‐(trans‐1,2‐ethenediyl) bisbenzene, commonly known as trans‐stilbene, and derivatives of trans‐stilbene substituted by methyl or methoxy side groups: 1,1’‐(trans‐1,2‐ethenediyl), bis‐2,5‐dimethylbenzene, and 1,1’‐(trans‐1,2‐ethenediyl) bis‐2,5‐dimethoxybenzene. Our results are discussed in light of recent experimental data on poly(paraphenylene vinylene), poly(dimethyl paraphenylene vinylene), and poly(dimethoxy paraphenylene vinylene).

Effect of Styryl Side Groups on the Photophysical Properties and Hole Mobility of PPE−PPV Systems

This contribution reports on the synthesis of defect-free styryl-substituted poly(p-phenylene−ethynylene)-alt-poly(p-phenylene−vinylene)s, DO- and MEH-ST-PPE2-PPV2, consisting of a 2:2 triple bond/double bond ratio in the main chain. A detailed and systematic comparison of their photophysical properties with those of solely alkoxy-substituted polymer O-8-PPE2-PPV2, highlighting the effect of the styryl side groups, has been carried out. The bis(styryl) substituents act on the one hand as electron donor to the main chain conjugation system and, on the other hand, form a separate bis(styryl)phenylene chromophore system. The resulting two-dimensional and separate conjugation construct in ST-PPE-PPV polymers is confirmed by the fluorescence excitation anisotropy curves, which reach the value 0 around 360 nm corresponding to the absorption of the bis(styryl) system. Thin film PL and EL spectra of MEH-ST-PPE2-PPV2 are red-shifted relative to DO-ST-PPE2-PPV2, due to strong π−π interchain interactions resulting from the grafting of methoxy side groups, potentially explaining the better EL performance of MEH- than DO-ST-PPE2-PPV2 LED device (glass substrate/ITO/PEDOT:PSS/ST-PPE2-PPV2/Ca/Ag) as well as the higher intrinsic hole mobility value, μhole (measured using CELIV technique) for MEH- (2.8 × 10-6 cm2/V·s) than DO-ST-PPE2-PPV2 (1.5 × 10-6 cm2/V·s). Both values are, however, at least 2-fold lower than that of O-8-PPE2-PPV2 (5.5 × 10-6 cm2/V·s) due to the twist in their conjugated backbone caused by the styryl side groups. Nevertheless, nonoptimized bulk heterojunction solar cells of ηAM1.5 around 1% were readily designed using MEH-ST-PPE2-PPV2 as donor and PCBM as acceptor in a 1:3 weight ratio.

THEORETICAL STUDIES OF ONE- AND TWO-PHOTON ABSORPTION PROPERTIES FOR SYMMETRIC MOLECULES BASED ON BIS(STILBENE)DIETHYLENE

In order to investigate the substituting effects on the two-photon absorption (TPA) cross-section and the position of the TPA peak, the one- and two-photon absorption properties of a series of symmetric molecules with bis(stilbene)diethylene π-conjugated bridge have been studied using ZINDO-SOS method. The transition moments from the ground state to the lowest excited state (M0k) and from the lowest excited state to the TPA final state (Mkn), together with the detuning energy ΔE = E0k - Ekn/2, were calculated using the INDO1 method included in the ZINDO program. The results indicate that bis-donor and bis-acceptor substitutions mainly affect the transition dipole moments M0k and Mkn, and that donor or acceptor side groups have a strong influence on the detuning energy. Meanwhile, it was found that the molecules with the bis-donor structure possess enhanced TPA cross sections, and the molecules with cyano or methoxy side groups have a large red-shift with respect to molecules without side groups.

Well-Packed Chains and Aggregates in the Emission Mechanism of Conjugated Polymers

We synthesized dialkoxy-substituted poly[phenylene vinylene]s (dROPPV-1/1, 0.2/1, and 0/1) consisting of two repeating units with different side-chain lengths (methoxy and 3,7-dimethyloctyloxy). These polymers can serve as a model system to clarify roles of aggregates (the sites with ground-state interchain interactions) and the independent chain segments in the well-packed chains (the chain segments that are compactly packed without interaction) in the emission mechanism of conjugated polymers. Due to the packing of polymer chains, films of all of these polymers are accessible to interchain excitations, after which excitons can re-form to result in delayed luminescence. Besides, some chains form aggregates so that the delayed luminescence is no more the ordinary single-chain emission but red-shifted and less structured. Not only the re-formation of these indirect excitons but also the aggregation of chains are facilitated in the polymers with short methoxy side groups, revealing that both packing and aggregation of chain segments require a short spacing between polymer chains. However, the incorporation of other side chains such as the 3,7-dimethyloctyloxy group to dROPPVs is necessary for the formation of aggregates because these long branched side chains can reduce the intrachain order imposed by the short methoxy groups, which accounts for the absence of aggregate emission in the well-studied poly[2,5-dimethoxy-1,4-phenylene vinylene]. This study reveals that the well-packed chains do not necessarily form aggregates. We also show that the photophysical properties and the film morphology of conjugated polymers can be deliberately controlled by fine-tuning of the copolymer compositions, without altering the optical properties of single polymer chains (e.g., as in dilute solutions).

Carotenoid-Induced Cooperative Formation of Bacterial Photosynthetic LH1 Complex

A simple reconstitution technique has been developed and then applied to prepare a series of light-harvesting antenna 1 (LH1) complexes with a programmed carotenoid composition, not available from native photosynthetic membranes. The complexes were reconstituted with different C(40) carotenoids, having two structural parameters variable: the functional side groups and the number of conjugated C-C double bonds, systematically increasing from 9 to 13. The complexes, differing only in the type of carotenoid, bound to an otherwise identical bacteriochlorophyll-polypeptide matrix, can serve as a unique model system in which the relationship between the carotenoid character and the functioning of pigment-protein complexes can be investigated. The reconstituted LH1 complexes resemble the native antenna, isolated from wild-type Rhodospirillum rubrum, but their coloration is entirely determined by carotenoid. Along with the increase in its conjugation size, the carotenoid absorption transitions gradually shift to the red. Thus, the extension of the conjugation size of the antenna carotenoids provides a mechanism for the spectral tuning of light harvesting in the visible part of the spectrum. The carotenoids in the reconstitution system promote the LH1 formation and seem to bind and transfer the excitation energy specifically only to a species with characteristically red-shifted absorption and emission maxima, apparently, due to a cooperative effect. Monitoring the LH1 formation by steady-state absorption and fluorescence spectroscopies reveals that in the presence of carotenoids it proceeds without spectrally resolved intermediates, leading directly to B880. The effect of the carotenoid is enhanced when the pigment contains the hydroxy or methoxy side groups, implying that, in parallel to hydrophobic interactions and pi-pi stacking, other interactions are also involved in the formation and stabilization of LH1.

IR Spectroscopic Study on the Hydration and the Phase Transition of Poly(vinyl methyl ether) in Water

The phase transitions of poly(vinyl methyl ether) (PVME) in H2O and D2O have been investigated by Fourier transform infrared (FTIR) spectroscopy. IR spectra of PVME solution are measured as a function of temperature, and changes in the spectra induced by the phase transition are observed. The IR bands attributable to the vibration modes of backbone and methoxy side group exhibit critical changes at a lower critical solution temperature (LCST). Heating of the solution above the LCST leads shifts of C−H stretching bands toward lower wavenumber during a high-wavenumber shift of C−O stretching band (ν(C−O)). Among the C−H stretching bands, symmetric and antisymmetric C−H stretching bands due to the methyl group (νs(CH3) and νas(CH3)) shift to the largest extent (20 cm-1). The νs(CH3) band is composed of two components centered at 2839 and 2820 cm-1, which are assignable to hydrated and dehydrated methyl species, respectively. The molar fraction of the hydrated methyl species is close to 1 below 36 °C and is nearly 0 above 40 °C, insisting that most of the methyl groups are dehydrated above the LCST, whereas the peak position of the ν(C−O) band indicates only partial dehydration of the ether group above the LCST. Though PVME concentration dependence of the peak positions of the νs(CH3) and the ν(C−O) bands measured below the LCST shows that dehydration of the methyl group and the ether oxygen initiates at different water/monomer ratios (methyl, 5.5; ether, 2.8), the dehydration of these groups simultaneously proceeds in the course of the phase transition.

Poly(ester amide)s Derived from l-Tartaric Acid and Amino Alcohols. 1. Regic Polymers

Stereoregular poly(ester amide)s (PEATn) containing equal amounts of ester and amide groups have been obtained by polycondensation in solution from di-O-methyl-l-tartaric acid and aliphatic amino alcohols H2N(CH2)n-1CH2OH. Suitable synthetic routes were designed to prepare either syndioregic (s-PEATn, n = 5,6) or isoregic (i-PEATn, n = 5, 6, 11) polymers. All the newly synthesized poly(tartarester amide)s were characterized by elemental analysis, size exclusion chromatography, and IR and NMR spectroscopies. They all display optical activity in solution and, except for s-PEAT5, are highly crystalline with Tm's within the range 100−150 °C and Tg's oscillating between 10 and 30 °C. Thermal decomposition of PEATn onsets above 200 °C with Td values depending upon both the regicity of the chain and the length of the polymethylene segment. For comparative purposes, two poly(esteramide)s, one syndioregic (s-PEAS6) and another isoregic (i-PEAS6), were prepared from succinic acid and 6-amino-1-hexanol, and their properties were evaluated in parallel. Major differences between PEAS6's and PEAT6's concerned solubility and hygroscopicity whereas crystallinity and thermal transitions were found to be scarcely affected by the presence of the methoxy side groups.