Types Of Side Groups Research Articles

Influence of conformation on electron transport properties of oligophenyleneimine molecular wires

We propose molecular wires based on oligophenyleneimine (OPI) sandwiched between two gold electrodes. The electron transport properties of molecular wires attached to side groups are investigated using steady-state theoretical model and density functional theory by using GAUSSIAN 09 software. We investigate the influence of the side group and torsion angle on the electronic properties of molecular wires. We calculate the spatial distribution of the frontier orbitals, energy gap, transmission probability and the current rectifying ratio for OPI, OPI-pyridine, OPI-pyrazine, OPI-thiophene and OPI-thiazole. The transmission spectra change remarkably depending on the type of side group and torsion angle. The current rectifying ratio will increase by increasing the difference between torsion angles depending on the type of side group. That means the OPI-side group can be employed in molecular electronics.

Modulation of spatial spin polarization at organic spinterface by side groups

Abstract Spin polarization at benzene/Ni organic/ferromagnetic interface is investigated by applying different substituting side groups. Based on first-principle calculations, it is demonstrated that the spin polarization of the states may be tuned in magnitude and sign by the side groups, which depends on the type of side groups as well as their position in the aromatic ring. Especially, a spatial spin polarization modulation is realized at the surface with the utilization of electron donating group NH 2 or electron accepting group NO 2. The analysis of projected density of states onto the p z orbital of carbon atoms indicates that the side group reduces the structural symmetry of the molecule and changes the p z orbital of carbon atom at different position, which further modifies the p z - d orbital hybridization as well as the spin transfer between the molecule and the ferromagnet. This work indicates a feasible way to modulate the spatial spin polarization at organic spinterface by side groups, which deserves to be measured by spin-polarized scanning tunneling microscopy.

Tuning the role of charge-transfer states in intramolecular singlet exciton fission through side-group engineering.

Understanding the mechanism of singlet exciton fission, in which a singlet exciton separates into a pair of triplet excitons, is crucial to the development of new chromophores for efficient fission-sensitized solar cells. The challenge of controlling molecular packing and energy levels in the solid state precludes clear determination of the singlet fission pathway. Here, we circumvent this difficulty by utilizing covalent dimers of pentacene with two types of side groups. We report rapid and efficient intramolecular singlet fission in both molecules, in one case via a virtual charge-transfer state and in the other via a distinct charge-transfer intermediate. The singlet fission pathway is governed by the energy gap between singlet and charge-transfer states, which change dynamically with molecular geometry but are primarily set by the side group. These results clearly establish the role of charge-transfer states in singlet fission and highlight the importance of solubilizing groups to optimize excited-state photophysics.

Reflectance spectroscopy (350–2500 nm) of solid-state polycyclic aromatic hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds based on fused aromatic rings, and are formed in a variety of astrophysical, solar nebula and planetary processes. Polycyclic aromatic hydrocarbons are known or suspected to occur in a wide variety of planetary settings including icy satellites, Titan’s hazes, carbonaceous meteorites, comet nuclei, ring particles; and terrestrial organic-rich lithologies such as coals, asphaltites, and bituminous sands. Relatively few measurements of the visible and near-infrared spectra of PAHs exist, yet this wavelength region (350–2500nm) is widely used for remote sensing. This study presents detailed analyses of the 350–2500nm reflectance spectra of 47 fine-grained powders of different high-purity solid-state PAHs. Spectral properties of PAHs change with variations in the number and connectivity of linked aromatic rings and the presence and type of side-groups and heterocycles. PAH spectra are characterized by three strong features near ∼880nm, ∼1145nm, and ∼1687nm due to overtones of νCH fundamental stretching vibrations. Some PAHs are amenable to remote detection due to the presence of diagnostic spectral features, including: NH stretching overtones at 1490–1515nm in NH- and NH2-bearing PAHs, aliphatic or saturated bond CH overtone vibrations at ∼1180–1280nm and ∼1700–1860nm; a broad asymmetric feature between ∼1450nm and ∼1900nm due to OH stretching overtones in aromatic alcohols, CH and CO combinations near ∼2000–2010nm and ∼2060–2270nm in acetyl and carboxyl-bearing PAHs. Other substituents such as sulphonyl, thioether ether and carboxyl heterocycles, or cyano, nitrate, and aromatic side groups, do not produce well-resolved diagnostic spectral features but do cause shifts in the positions of the aromatic CH vibrational overtone features. Fluorescence is commonly suppressed by the presence of heterocycles, side-groups and in many non-alternant PAHs. The spectral characteristics of PAHs offer the potential, under suitable circumstances, for remote characterization of the classes of PAH present and in some cases, identification of particular heterocyclic or side-group substituents.

ChemInform Abstract: Generation of Structural Diversity in Polyphosphazenes

AbstractReview: 59 refs.

Generation of structural diversity in polyphosphazenes

Polyphosphazenes are macromolecules with a chain of alternating phosphorus and nitrogen atoms and with two (usually) organic side groups linked to each phosphorus. Although the earliest poly(organophosphazenes) were essentially linear polymers each bearing only one type of side group along the chain, research in our program in recent years has widened the scope to include mixed‐substituent polymers with two or more different side groups, block copolymers, comb structures, stars, and dendrimers, all with a wide variety of different properties. In addition, supramolecular systems have also been synthesized including vesicles, microspheres, and a variety of composite systems. This review provides a summary of these developments together with an introduction to the widening array of developing uses. Copyright © 2013 John Wiley & Sons, Ltd.

Tris-cis-tris-trans-dodeca[organo(dimethylorganosiloxy)]cyclododecasiloxanes {RSi(O)[OSiMe2R′]}12. Self-Ordering Features

The molecular order and thermotropic transitions of tris-cis-tris-trans-dodeca- [organo(dimethylorganosiloxy)]cyclododecasiloxanes {RSi(O)[OSiMe(2)R']}(12) (R = Ph, R' = Me, CH(2)Cl, Vi; R = Me, Et, Vi, R' = Me) have been investigated using differential scanning calorimetry, thermogravimetric analysis, and X-ray scattering. The cyclododecasiloxanes with phenyl side groups (R = Ph) can form mesomorphic structures within a very wide temperature range. Compounds with R = Me and Vi are liquids and exhibit microphase separation above their glass transition temperature because of the different nature and structure of the organic R and trimethylsiloxy OSiMe(3) side groups. When the side group R = Et, a mesomorphic structure is formed in a substantially more narrow temperature region than that for cycles containing phenyl groups. Thus, the type of side group R in organocyclododecasiloxanes determines their ability for self-ordering into mesomorphic structures and the thermal stability of the mesomorphic state.

Molecular Basis of Phospholipase A 2 Activity toward Phospholipids with sn-1 Substitutions

We studied secretory phospholipase A 2 type IIA (sPLA 2) activity toward phospholipids that are derivatized in the sn-1 position of the glycerol backbone. We explored what type of side group (small versus bulky groups, hydrophobic versus polar groups) can be introduced at the sn-1 position of the glycerol backbone of glycerophospholipids and at the same time be hydrolyzed by sPLA 2. The biophysical characterization revealed that the modified phospholipids can form multilamellar vesicles, and several of the synthesized sn-1 functionalized phospholipids were hydrolyzed by sPLA 2. Molecular dynamics simulations provided detailed insight on an atomic level that can explain the observed sPLA 2 activity toward the different phospholipid analogs. The simulations revealed that, depending on the nature of the side chain located at the sn-1 position, the group may interfere with an incoming water molecule that acts as the nucleophile in the enzymatic reaction. The simulation results are in agreement with the experimentally observed sPLA 2 activity toward the different phospholipid analogs.

New mesomorphic organocyclosiloxanes II. Thermal behaviour and mesophase structure of organocyclohexasiloxanes†

Investigations of thermotropic phase transitions performed on organocyclosiloxanes [PhSi(O)OSiR]6, where R is Me3, Me2(CH2Cl) or Me2(CH≃CH2), have revealed that all these hexamers are mesomorphic compounds. The hexamers exhibit uncommon polymesomorphic behaviour forming two quite different mesomorphic structures. The molecular arrangement in the low temperature (LT) modification is characterized by two-dimensional (2D) long-range order with hexagonal packing. The X-ray diffraction pattern and peculiarities of molecular packing in the crystal lead us to suggest that the LT-mesophase is columnar, presumably of the Colhd type. The LT-mesophase is formed by dimeric moieties, which associate with each other in column-like substructures, the ring planes not orthogonal to the stack axis. The high temperature (HT) mesophase is a plastic crystal (3D-order), where molecules take up positions in a face-centred cubic lattice. This is a very uncommon example of thermal behaviour for plastic crystals that provides a unique opportunity to bridge the gap between plastic crystalline and liquid crystalline mesomorphic behaviour. The thermal and structural properties of the mesophases depend upon the type of side groups of the hexamers. The size of the ring also affects the phase behaviour and the mesomorphic structure. This conclusion is consistent with data obtained by us earlier for cyclotetrasiloxanes.

The First Linear Multiphosphazene Having Five Different Types of Side Groups and Its Use as the Core of a Dendrimeric Species.

The step-by-step synthesis of the first oligophosphazenes having more than two types of side functions is described. These multifunctionalized oligophosphazenes possess up to four phosphazene linkages and up to four types of functional side groups. These compounds may serve as models for a better understanding of electronic delocalization phenomena in linear inorganic chains, and constitute novel cores for the synthesis of new dendrimeric species possessing several types of functions as end groups, at the level of the core, and within the branches.

The first linear multiphosphazene having five different types of side groups and its use as the core of a dendrimeric species.

The step-by-step synthesis of the first oligophosphazenes having more than two types of side functions is described. These multifunctionalized oligophosphazenes possess up to four phosphazene linkages and up to four types of functional side groups. These compounds may serve as models for a better understanding of electronic delocalization phenomena in linear inorganic chains, and constitute novel cores for the synthesis of new dendrimeric species possessing several types of functions as end groups, at the level of the core, and within the branches.

Comparison of mixed trialkyl phosphine oxides (TRPO) extractants from different sources

Mixed trialkyl phosphine oxides (TRPO) are promising extractants. They may be used to recover radionuclides from highly radioactive liquid wastes. However, since TRPOs contain alkyl chains ranging from C4 to C8, different TRPO may have different characteristics. In this paper, four TRPOs from different sources are compared. The extraction and back-extraction characteristics for UO 2 2+, Pu 4+, Am 3+, and TcO 4 − were investigated, and the loading capacities for both of UO 2 2+ and HNO 3 were compared. Infrared spectroscopy and pyrolysis gas chromatography were used to analyze the type and composition of the side-group in these TRPOs. The experimental results demonstrate that different TRPOs possess similar extraction and back-extraction characteristics because they have the same type of side-group. However, different TRPOs show different loading capacity for UO 2 2+ and HNO 3 due to differences in the alkyl composition of the side-group.

Inhibition of Type 304 Stainless Steel Corrosion in 2 M Sulfuric Acid by Some Benzoazoles—Time and Temperature Effects

Abstract 2-methyl benzoazole and 2-mercapto benzoazole derivatives were investigated as corrosion inhibitors for Type 304 (UNS S30400) stainless steel in 2 M sulfuric acid (H2SO4) solution using weight loss, gasometry, and alternating current (AC) impedance techniques. Effect of immersion time and temperature were studied. The observed inhibition efficiency was found to depend on the heteroatom and type of side group. The efficiency of 2-methyl benzoselenazole (MBS), 2-mercapto benzoimidazole (CBI), and 2-mercapto benzothiazole (CBT) were independent of immersion time. However, MBS presented an efficiency of ∼ 90% at 45°C and caused a decrease in the activation energy of the corrosion process. Similarly, CBI and CBT had high efficiencies that remained almost unchanged at temperatures between 25°C and 55°C, but their activation energies increased slightly compared to that in their absence. Chemisorption of inhibitor molecules was used to explain the results of this study.

Molecular Structure and Electrical Insulating Properties of Grafted and Cyanoethylated Cellulose

Cyanoethylation of cellulose and Grafting of cellulose (bleached viscose wood pulp (VWP)} & cyanoethyl cellulose are carried out. The nitrogen content of these cellulose derivatives is determined. Grafted cyanoethyl cellulose has the highest nitrogen content (12.5%). FT/IR spectra of these derivatives showed a new band at 2225cm−1 in the spectra of cyanoethyl and grafted cellulose which is the characteristic band for -C ═ N stretching vibration. Also, a new band appeared at 1720cm−1 in case of grafted cyanoethyl cellulose, which is the characteristic band for C ═ O stretching vibration. The crystallinity index (A 1435/A 900 cm−1) of cyanoethyl cellulose is lower than that in case of cellulose and grafted cellulose. The thermal study shows three endothermic peaks for grafted cyanoethyl cellulose while as cellulose, grafted and cyanoethyl cellulose has one endothermic peaks. The dielectric properties depend on the nitrogen content. These observations are closely correlated with the structure of the products such as types of side groups and the interaction between them.

Computer simulation of polyolefin interfaces

Interfaces, thin films and amorphous cells of several hydrocarbon polymers are studied with atomistic computer simulation. Solubility parameters, surface tensions and interfacial tensions are evaluated from the computed structures. These structures are constructed using Molecular Dynamics and Molecular Mechanics techniques. The various components of the energetic interactions (torsional, vdW, etc.) are examined in detail in order to gain an insight into the nature of the regular and anomalous interactions between these films.The polymers studied in this article are all are atactic linear hydrocarbons and have approximately 200 carbons in the backbone chain. These include polypropylene (PP), head to head polypropylene (hhPP), a polymer which is termed P78 (a random copolymer composed of 22% of a linear (–CH2CH2CH2CH2–) monomer and 78% of a branched (–CH2CH(C2H5)–) monomer), polyethylenepropylene (PEP), and PE2P2 (an alternating copolymer consisting of two ethylene (E) and two propylene (P) monomers in the repeating pattern (–(EEPP)n–)). The primary difference between the different polymers studied is the type of side group (ethyl or methyl) and the location, frequency and spacing of that group.Interfaces formed with the same polymer type (PP–PP, PEP–PEP, P78–P78) yield a surface tension close to zero as expected. Attractive interactions between some of the pairs of films is found in the simulation. The distribution among the energetic terms seems to indicate that this attractive interaction is brought about by favorable local intramolecular energetic terms rather than simply by van der Waals interactions alone.

Competition of Alignment and Aggregation? Phenomena in Constrained Films of LC Poly (Olefin Ulfone)s and Maleic Anhydride Co- and Terpolymers

Anisotropic films of functionalised polymers such as the liquid crystalline poly (olefin sulfone)s (POS) and maleic anhydride co- and terpolymers (MAC, containing azobenzene side-groups too) are studied. Starting from isotropic spin-coated films annealing results in homeotropically aligned films by spontaneous self-assembling. X-ray specular scattering (XRS) and X-ray grazing incidence diffraction (GIXD) indicate a layered structure across the film parallel to the interface and significant in-plane order in thin films. Polarised UV-VIS spectroscopy investigations show that the homeotropic orientation of the side groups causes the formation of “card packed” or H-aggregates. For azobenzene containing MAC terpolymer an initial UV-irradiation followed by a polarised VIS-irradiation causes a light-induced co-operative reorientation of both types of side-groups and results in a lamellar stacking which is tilted. Orientation and aggregation are therefore driven by the liquid crystallinity and the segregation tendency of POS and MAC in constrained films. This seems to be an important factor for such spontaneous ordering processes.

Synthesis and characterization of soluble aromatic polyesters derived from substituted terphenyl and quinquephenyl diols

Rigid aromatic polyesters containing alkoxy or phenyl-substituted oligophenyls were prepared. Soluble polymers were obtained also in cases where phenyl-substituted quinquephenyl diols were combined with asymmetric phenyl-substituted terephthalic acid. The synthesized polyesters were characterized by viscosimetry, gel permeation chromatography, thermal analysis, and dynamic mechanical analysis. The temperature dependence of the intrinsic viscosity was sensitive to the type of side groups. Thermogravimetry has shown that polyesters with aromatic substituents were stable up to 380–400°C. The glass transition temperatures of the polyesters with aromatic side groups were in the 220–260°C range as determined by DSC. Polyesters with hexyloxy side chains show crystallinity. Dynamic mechanical analysis showed that in the cases where aromatic substituents were used to increase solubility, the obtained polymers have very useful mechanical properties at high temperatures. The polymer having the quinquephenyl unit in the main chain has an almost constant modulus up to 340°C. © 1996 John Wiley & Sons, Inc.

Mark−Houwink−Kuhn−Sakurada Exponent at the ϑ Condition. Its Invariancy with Respect to the Cross-Sectional Dimensions of Polymer Chains

The question raised by Fujita has been examined, namely why the intrinsic viscosity of many polymers at the Θ condition [η] 0 is proportional to M 1/2 over a broad range of molecular weights. An explanation is proposed, based on a combination of the theory of the wormlike cylinder model with reported data on cross-sectional dimensions of 30 polymers with the carbon backbone differing in both the size and type of side groups (vinyl polymers, polyacrylates, polymethacrylates). The behaviors of poly(dimethylsiloxane) and poly(ethylene oxide), which are not in line with this explanation, are briefly discussed.

Room Temperature Ferroelectric Terpolymers with Large Spontaneous Polarization

It is well-known that the mesomorphic range as well as the physical properties of low molecular weight mesogens can be tuned by mixing different types of monomers. We show here that a similar tuning can be achieved for side-chain liquid crystalline polymers by incorporating two different types of side groups in the backbone in different ratios. The transition temperatures of these terpolymers show a linear dependence on the ratio of the two mesogenic side groups, while their spontaneous polarization shows nonmonotonic dependence. Also, the spontaneous polarization of the terpolymers shows an unusual (linear) temperature dependence throughout the smectic C* phase.

Electronic properties of polydiheteroarylenemethines: Electrical conductivity

AbstractPolydiheteroarylenemethines show a relatively high electrical conductivity. Two‐coplanar‐electrode measurements give a high surface conductivity of 10−9 S/□ and a high mobility up to 1 cm2 V−1. Depending on the type of side group, doping with iodine served to raise the conductivity by five orders of magnitude. Optical absorption analysed with DC and AC conductivity data revealed two components in the transport process: A VHR (variable range hopping) process shifting to a band tail polaronic process as the degree of polymerisation increases, corresponding to a very characteristic transition in the AC conductivity. The hopping process corresponds to an AC conductivity frequency power law dependence of ω0.66, whereas the polaronic process corresponds to a power law dependence of ω0.1.