This document discusses the synthesis and characterization of three-ring mesogens with a terminal dimethylamino group. Key findings include:
1. Three mesogens were synthesized with varying alkyl chain lengths. Differential scanning calorimetry and polarized optical microscopy showed the compounds exhibited nematic and smectic A phases.
2. X-ray diffraction of one compound (DdIMPDB) surprisingly found an interdigitated smectic A layer organization, which is uncommon for dimethylamino-based mesogens.
3. Density functional theory calculations and NMR spectroscopy were used to determine molecular geometry and carbon chemical shifts for structural analysis. Photophysical properties also indicated intramolecular charge transfer interactions.
4. Solid-
This document summarizes recent developments in side chain liquid crystal polymers, focusing on polysiloxane based polymers. It discusses how a series of these polymers were prepared with systematic variation in the spacer length between the mesogenic units and the polymer backbone. Electro-optic measurements found that increasing the spacer length lowered the threshold voltage for molecular reorientation. A simple model indicates this is due to changes in intrinsic curvature elasticity rather than orientational order as the constraints from the polymer backbone are reduced with longer spacers.
Study of Microstructural, Electrical and Dielectric Properties of La0.9Pb0.1M...Scientific Review SR
The present work studies the microstructural and electrical properties of La0.9Pb0.1MnO3 and La0.8Y0.1Pb0.1MnO3 ceramics synthesized by solid-state route method. Microstructure and elemental analysis of both samples were carried out by field emission scanning electron microscope (FESEM) and energy dispersive spectroscopy (EDS) method, respectively. Phase analysis by X-ray diffraction (XRD) indicated formation of single phase distorted structure. The XRD data were further analyzed by Rietveld refinement technique. Raman analysis reveals that Y atom substitutes La site into the LPMO with shifting of phonon modes. The temperature variation of resistivity of undoped and Y-doped La0.9Pb0.1MnO3 samples have been investigated. The electrical resistivity as a function of temperature showed that all samples undergo an metal-insulator (M-I) transition having a peak at transition temperature TMI. Y-doping increases the resistivity and the metal-insulator transition temperature (TMI) shifts to lower temperature. The temperature-dependent resistivity for temperatures less than metal-insulator transition is explained in terms the quadratic temperature dependence and for T > TMI, thermally activated conduction (TAC) is appropriate. Variation of frequency dispersion in permittivity and loss pattern due to La-site substitution in LPMO was observed in the dielectric response curve.
This document describes the synthesis and characterization of a novel redox-based chiroptically switching polymer. The polymer was prepared by grafting electrochromic viologen groups onto the side chains of an optically active conjugated polymer backbone containing 1,1'-binaphthyl units. The resulting polymer exhibited a much larger optical rotation and intense circular dichroism signal compared to a small molecule model compound, indicating secondary chirality in the main polymer chain. The polymer undergoes distinctive and reversible color changes from light yellow to dark blue upon electrochemical or chemical reduction/oxidation of the viologen units, accompanied by changes in its circular dichroism spectrum. This allows for redox-driven chiroptical switching behavior
The document presents a study of mixtures of spiropyran (SP) and a mesogenic diacrylate monomer (RM257). Key points:
1) A phase diagram was established for SP/RM257 mixtures using differential scanning calorimetry and polarized optical microscopy. This showed various coexistence regions involving crystals, nematic phases, and isotropic liquids.
2) A theoretical phase diagram was also calculated by combining Flory-Huggins, Maier-Saupe, and phase field free energy models. This accounted for liquid-liquid demixing, nematic ordering, and crystal solidification.
3) UV irradiation was found to lower the melting points of SP and SP/
The cholesteric liquid-crystal poly[oxycarbonyl-1,4-phenylene-oxy-1,4 terephthaloyl-oxy-1,4-phenylenecarbonyloxy(
1,2-dodecane)] [C34H36O8]n, named PTOBDME, synthesized by polycondensation reaction from
equimolar quantities of TOBC and the racemic mixture of glycol (R-S-1,2 dodecanediol), exhibits unexpected
optical activity and chiral morphology. The structure of racemic-PTOBDME, under different polymerization
kinetics conditions, is analyzed by conventional NMR techniques and compared with those of polymer
enantiomers R-PTOBDME and S-PTOBDME obtained starting R(+)1,2 and S(-)1,2-dodecanediol respectively.
Molecular models based on the NMR signals intensities are proposed. The optical activity of racemic-
PTOBDME is evaluated by measuring the ORD values during kinetics study, and compared to the chiral
polymers. Each enantiomeric polymer seems to present the same stereoregular head-tail, isotactic structure than
the racemic, which we explain by the higher reactivity of the primary hydroxyl than the secondary one in the
glycol through polycondensation. For each enantiomer, two independent sets of signals were observed by NMR,
explained as two diastereomeric helical conformers: gg and gt, related with two possible staggered
conformations, along the copolymer backbone. Chirality in racemic-PTOBDME is proposed to be due to the
kinetic resolution of a preferable helical diastereomer, such as Sgt, with respect to the possible four forms, while
the R/S ratio of asymmetric carbon atoms remained 50:50. Chiral amplification is observed in R-PTOBDME and
S-PTOBDME due to a helical screw sense excess. Optimum yield was obtained for racemic PTOBDME, after
120 minutes polycondensated and decanted in toluene for 24 hours. Two weeks later a second fraction
precipitated from the toluene mother liquor with 67.6% chiral excess. After eight months and two weeks a third
fraction precipitated with 85.2% chiral excess.
Synthesis of flower-like magnetite nanoassembly: Application in the efficient...Pawan Kumar
A facile approach for the synthesis of magnetite microspheres with flower-like morphology is reported
that proceeds via the reduction of iron(III) oxide under a hydrogen atmosphere. The ensuing magnetic
catalyst is well characterized by XRD, FE-SEM, TEM, N2 adsorption-desorption isotherm, and
Mössbauer spectroscopy and explored for a simple yet efficient transfer hydrogenation reduction of a
variety of nitroarenes to respective anilines in good to excellent yields (up to 98%) employing hydrazine
hydrate. The catalyst could be easily separated at the end of a reaction using an external magnet and
can be recycled up to 10 times without any loss in catalytic activity.
Functionalization of Diazomethyl Aromatic Compounds onto Single Wall Carbon N...drboon
One of the most fascinating and remarkable formulas existing in mathematics is the Euler Formula. It was formulated in 1740, constituting the main factor to reason why humankind can advance in science and mathematics. Accordingly, this research will continue investigating the potentiality of the Euler Formula or "the magical number e." The goal of the present study is to further assess the Euler formula and several of its applications such as the compound interest problem, complex numbers, trigonometry, signals (electrical engineering), and Ordinary Differential Equations. To accomplish this goal, the Euler Formula will be entered into the MATLAB software to obtain several plots representing the above applications. The importance of this study in mathematics and engineering will be discussed, and a case study on a polluted lake will be formulated.
This document discusses the use of positron annihilation spectroscopy to analyze the free volume nanohole distribution in polymers and its correlation to the physico-chemical properties of polymers. It provides background on positron annihilation spectroscopy and how it can be used to measure free volume in polymers. The document then describes several studies that use this technique to analyze the influence of free volume properties on the swelling of polymer hydrogels, structure-property relationships in modified epoxy resins, and free volume and interfacial interactions in epoxy clay composites.
This document summarizes recent developments in side chain liquid crystal polymers, focusing on polysiloxane based polymers. It discusses how a series of these polymers were prepared with systematic variation in the spacer length between the mesogenic units and the polymer backbone. Electro-optic measurements found that increasing the spacer length lowered the threshold voltage for molecular reorientation. A simple model indicates this is due to changes in intrinsic curvature elasticity rather than orientational order as the constraints from the polymer backbone are reduced with longer spacers.
Study of Microstructural, Electrical and Dielectric Properties of La0.9Pb0.1M...Scientific Review SR
The present work studies the microstructural and electrical properties of La0.9Pb0.1MnO3 and La0.8Y0.1Pb0.1MnO3 ceramics synthesized by solid-state route method. Microstructure and elemental analysis of both samples were carried out by field emission scanning electron microscope (FESEM) and energy dispersive spectroscopy (EDS) method, respectively. Phase analysis by X-ray diffraction (XRD) indicated formation of single phase distorted structure. The XRD data were further analyzed by Rietveld refinement technique. Raman analysis reveals that Y atom substitutes La site into the LPMO with shifting of phonon modes. The temperature variation of resistivity of undoped and Y-doped La0.9Pb0.1MnO3 samples have been investigated. The electrical resistivity as a function of temperature showed that all samples undergo an metal-insulator (M-I) transition having a peak at transition temperature TMI. Y-doping increases the resistivity and the metal-insulator transition temperature (TMI) shifts to lower temperature. The temperature-dependent resistivity for temperatures less than metal-insulator transition is explained in terms the quadratic temperature dependence and for T > TMI, thermally activated conduction (TAC) is appropriate. Variation of frequency dispersion in permittivity and loss pattern due to La-site substitution in LPMO was observed in the dielectric response curve.
This document describes the synthesis and characterization of a novel redox-based chiroptically switching polymer. The polymer was prepared by grafting electrochromic viologen groups onto the side chains of an optically active conjugated polymer backbone containing 1,1'-binaphthyl units. The resulting polymer exhibited a much larger optical rotation and intense circular dichroism signal compared to a small molecule model compound, indicating secondary chirality in the main polymer chain. The polymer undergoes distinctive and reversible color changes from light yellow to dark blue upon electrochemical or chemical reduction/oxidation of the viologen units, accompanied by changes in its circular dichroism spectrum. This allows for redox-driven chiroptical switching behavior
The document presents a study of mixtures of spiropyran (SP) and a mesogenic diacrylate monomer (RM257). Key points:
1) A phase diagram was established for SP/RM257 mixtures using differential scanning calorimetry and polarized optical microscopy. This showed various coexistence regions involving crystals, nematic phases, and isotropic liquids.
2) A theoretical phase diagram was also calculated by combining Flory-Huggins, Maier-Saupe, and phase field free energy models. This accounted for liquid-liquid demixing, nematic ordering, and crystal solidification.
3) UV irradiation was found to lower the melting points of SP and SP/
The cholesteric liquid-crystal poly[oxycarbonyl-1,4-phenylene-oxy-1,4 terephthaloyl-oxy-1,4-phenylenecarbonyloxy(
1,2-dodecane)] [C34H36O8]n, named PTOBDME, synthesized by polycondensation reaction from
equimolar quantities of TOBC and the racemic mixture of glycol (R-S-1,2 dodecanediol), exhibits unexpected
optical activity and chiral morphology. The structure of racemic-PTOBDME, under different polymerization
kinetics conditions, is analyzed by conventional NMR techniques and compared with those of polymer
enantiomers R-PTOBDME and S-PTOBDME obtained starting R(+)1,2 and S(-)1,2-dodecanediol respectively.
Molecular models based on the NMR signals intensities are proposed. The optical activity of racemic-
PTOBDME is evaluated by measuring the ORD values during kinetics study, and compared to the chiral
polymers. Each enantiomeric polymer seems to present the same stereoregular head-tail, isotactic structure than
the racemic, which we explain by the higher reactivity of the primary hydroxyl than the secondary one in the
glycol through polycondensation. For each enantiomer, two independent sets of signals were observed by NMR,
explained as two diastereomeric helical conformers: gg and gt, related with two possible staggered
conformations, along the copolymer backbone. Chirality in racemic-PTOBDME is proposed to be due to the
kinetic resolution of a preferable helical diastereomer, such as Sgt, with respect to the possible four forms, while
the R/S ratio of asymmetric carbon atoms remained 50:50. Chiral amplification is observed in R-PTOBDME and
S-PTOBDME due to a helical screw sense excess. Optimum yield was obtained for racemic PTOBDME, after
120 minutes polycondensated and decanted in toluene for 24 hours. Two weeks later a second fraction
precipitated from the toluene mother liquor with 67.6% chiral excess. After eight months and two weeks a third
fraction precipitated with 85.2% chiral excess.
Synthesis of flower-like magnetite nanoassembly: Application in the efficient...Pawan Kumar
A facile approach for the synthesis of magnetite microspheres with flower-like morphology is reported
that proceeds via the reduction of iron(III) oxide under a hydrogen atmosphere. The ensuing magnetic
catalyst is well characterized by XRD, FE-SEM, TEM, N2 adsorption-desorption isotherm, and
Mössbauer spectroscopy and explored for a simple yet efficient transfer hydrogenation reduction of a
variety of nitroarenes to respective anilines in good to excellent yields (up to 98%) employing hydrazine
hydrate. The catalyst could be easily separated at the end of a reaction using an external magnet and
can be recycled up to 10 times without any loss in catalytic activity.
Functionalization of Diazomethyl Aromatic Compounds onto Single Wall Carbon N...drboon
One of the most fascinating and remarkable formulas existing in mathematics is the Euler Formula. It was formulated in 1740, constituting the main factor to reason why humankind can advance in science and mathematics. Accordingly, this research will continue investigating the potentiality of the Euler Formula or "the magical number e." The goal of the present study is to further assess the Euler formula and several of its applications such as the compound interest problem, complex numbers, trigonometry, signals (electrical engineering), and Ordinary Differential Equations. To accomplish this goal, the Euler Formula will be entered into the MATLAB software to obtain several plots representing the above applications. The importance of this study in mathematics and engineering will be discussed, and a case study on a polluted lake will be formulated.
This document discusses the use of positron annihilation spectroscopy to analyze the free volume nanohole distribution in polymers and its correlation to the physico-chemical properties of polymers. It provides background on positron annihilation spectroscopy and how it can be used to measure free volume in polymers. The document then describes several studies that use this technique to analyze the influence of free volume properties on the swelling of polymer hydrogels, structure-property relationships in modified epoxy resins, and free volume and interfacial interactions in epoxy clay composites.
This document presents a study using density functional theory calculations to examine the adsorption of titanium dioxide nanostructures on pure and functionalized single-walled carbon nanotubes. The study finds that TiO2 nanostructures preferentially adsorb to chemical adsorption sites on functionalized SWCNTs, such as epoxy, alcohol, and carboxylate sites, compared to physical adsorption sites on pure SWCNTs, such as top, bridge, and hollow sites. Partial density of states calculations and charge density maps provide insight into the electronic structure and charge transfer between TiO2 nanostructures and SWCNTs. The results provide a theoretical understanding of controlled growth mechanisms of TiO2 nanostructures on carbon nanotube substrates.
Structural and Dielectric Properties of Lanthanum Substituted Lead ZirconateT...iosrjce
IOSR Journal of Applied Physics (IOSR-JAP) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
This study uses density functional theory calculations to examine the interaction between titanium oxide nanostructures and graphene or functionalized graphene nanoribbons (GNRs). The key findings are:
1) Rutile titanium dioxide favors physisorption on pure graphene, while rutile and anatase titanium dioxide show similar chemisorption on functionalized GNRs.
2) Charge density maps show the importance of electron distribution in the chemical interaction between titanium dioxide and graphene.
3) Analysis of partial density of states reveals the strength of binding energies at specific adsorption sites on the titanium dioxide/graphene systems.
4) The results provide insight into controlled growth mechanisms that could have applications in photovolta
Facile Synthesis and Characterization of Pyrolusite, β-MnO2, Nano Crystal wit...Editor IJCATR
MnO2 nanoparticles have been synthesized by a simple combustion method using MnSO4.4H2O. The crystalline phase, morphology, optical property and magnetic property of the as prepared nanoparticle were characterized using XRD, FT-IR, FT-Raman, SEM, UV-Vis, PL and VSM respectively. Structural studies by XRD indicate that the synthesized material as tetragonal rutile crystal structure. FT-IR and FT-Raman analysis revealed the stretching vibrations of metal ions in tetrahedral co-ordination confirming the crystal structure. The PL and UV analysis having an emission band at 390 nm, showed a prominent blue peak at 453 nm as well as a green emission lines at 553 nm with band gap energy of 3.2eV. Magnetic measurements indicate that the Néel temperature of the β-MnO2 structures is 92.5K for Hc = 100 Oe which showed antiferromagnetic behaviour.
A study the effect of zr o3 on the electrical and mechanical propertiesAlexander Decker
This document summarizes a study on the effect of adding ZrO3 on the electrical and mechanical properties of PMMA-Cr2O3 polymer composites. The study found that adding ZrO3 increased the electrical conductivity and ultrasound velocity of the composites. It also increased the relaxation amplitude, relaxation time, and bulk modulus while decreasing the molar conductivity, disintegration degree, and compressibility. The changes in properties are due to interactions between the polymer matrix and ZrO3 filler on the molecular level that affect ion motion and polymer chain structure. The addition of ZrO3 thus improves both the electrical and mechanical properties of the PMMA-Cr2O3 composite for applications.
International Journal of Research in Engineering and Science is an open access peer-reviewed international forum for scientists involved in research to publish quality and refereed papers. Papers reporting original research or experimentally proved review work are welcome. Papers for publication are selected through peer review to ensure originality, relevance, and readability.
This document summarizes the calculation of translational friction and intrinsic viscosity for four globular proteins (ribonuclease A, lysozyme, myoglobin, and chymotrypsinogen A) using their detailed atomic structures. The inclusion of a 0.9 Angstrom thick hydration shell around each protein allows the calculated translational friction and intrinsic viscosity to match experimental measurements. This hydration shell thickness corresponds to a hydration level of 0.3-0.4 grams of water per gram of protein, consistent with measurements from other techniques. Using detailed protein structures thus allows hydrodynamic measurements to support a unified picture of protein hydration, in contrast to earlier models that treated proteins as ellipsoids and found widely varying hydr
Electrodeposited pt on three dimensional interconnected graphene as a free st...tshankar20134
The document summarizes research on using a three-dimensional interconnected graphene structure as an electrode support for platinum nanoparticles for fuel cell applications. Key points:
1) Graphene was grown into a 3D foam-like structure using chemical vapor deposition on a nickel foam template, creating a seamless porous structure with high surface area and conductivity.
2) Platinum nanoparticles were deposited on the 3D graphene using pulsed electrodeposition, allowing control over particle size and uniform dispersion.
3) The 3D graphene with platinum nanoparticles showed improved catalytic activity for methanol oxidation compared to carbon fibers, due to the unique 3D structure, high surface area, and high conductivity of the graphene support.
Literature Seminar on Expansion of Pd chains through Beta-Carotene & Tetrapho...Nina Saraei
The document summarizes two papers on the expansion of palladium chains using β-carotene and tetraphosphine ligands. The first paper discusses the stepwise expansion of homonuclear and heteronuclear palladium chains from binuclear Pd(I) complexes supported by tetraphosphine ligands. Characterization data showed the complexes adopt linear structures with reversible metalation/demetalation. The second paper examines a bis-β-carotene ligand's ability to bind decanuclear palladium and palladium-platinum complexes into infinite π-stacked columns. Both papers demonstrate the use of multidentate ligands to control the assembly of extended metal atom chains.
This document summarizes research on the synthesis and characterization of nanobuilding blocks based on functionalized silsesquioxane cages. The researchers synthesized a series of [o-4-RStyrPhSiO1.5] cages of different sizes and degrees of functionalization via Heck coupling reactions. They characterized the compounds using various analytical techniques and studied their photophysical properties, including absorption, emission, and two-photon absorption. Unexpected photophysical behaviors were observed that depended on the functional group, cage geometry and degree of substitution. Density functional theory modeling supported the hypothesis that asymmetric bromination during synthesis led to asymmetrically functionalized cages with unusual polarization effects, explaining the observed photophysical properties.
Abstract
A small set of amphetamines has been analyzed by gas chromatography (GC) high-resolution time-of-flight mass spectrometry (TOFMS) using a microplasma photoionization (MPPI) soft-ionization source. This plasma-based, wavelength selectable ionization source enables ionization of the test compounds and their corresponding derivatives at ~8-12 eV that is a softer alternative to electron ionization at 70 eV. Three plasma gases were used in this study: Xe plasma that emits photons at resonance lines of 9.57 eV and 8.44 eV; Kr plasma at 10.63 eV and 10.02 eV, and Ar plasma at 11.82 eV and 11.61 eV. Derivatization of the test compounds with trifluoroacetic anhydride and α-methoxy-α-(trifluoromethyl)-phenylacetyl pyrazole was evaluated because the MPPI mass spectra of the underivatized amphetamines yield primarily iminium ions, which make the identification of the test compounds by GC-TOFMS inconclusive. The MPPI mass spectra of the TFA-derivatized amphetamines yield abundant molecular ions, when using Xe as plasma gas, and enough fragment ions with the Ar plasma that can help in formula generation. The structure elucidation of two "known unknowns" designer drugs using this "tunable" soft-ionization source and a high-resolution TOF mass spectrometer is presented in this study.
A facile route for nitrogen doped hollow graphitic carbonumarkhalid532
1) A facile route is presented for synthesizing nitrogen-doped hollow graphitic carbon spheres (NHGCSs) through the direct pyrolysis of solid melamine–formaldehyde (MF) resin spheres.
2) The MF resin spheres are prepared via a hydrothermal method without templates or catalysts, and pyrolyzed at temperatures above 400°C to form hollow carbon spheres with graphitic carbon shells.
3) The NHGCSs exhibit excellent capacitive performance as electrode materials for supercapacitors, achieving a high specific capacitance of 306 Fg-1 at 0.1 A g-1.
The document reports on research into the E. coli protein CusF. Key findings include:
1) The crystal structure of CusF bound to Ag(I) was determined to 1.0 angstrom resolution, revealing Ag(I) is coordinated by methionines M47 and M49 and histidine H36 in a beta barrel structure similar to the apo structure.
2) EXAFS was used to study CusF bound to Cu(I) since crystals could not be grown, showing Cu(I) is in a three-coordinate environment involving the same ligands.
3) Together the structures provide insight into how CusF sequesters toxic Cu(I) and Ag
This document describes a study investigating the effect of bridge length in new dinuclear constrained geometry catalysts (DCGCs) on the copolymerization behaviors of ethylene and styrene. Three new DCGCs were synthesized with bridge lengths of para-phenyl (10), para-xylyl (11), and para-diethylenephenyl (12). Copolymerization tests showed that catalyst activity, molecular weight of the copolymers, and styrene content all increased with increasing bridge length. Specifically, catalysts 11 and 12 showed activities 4-5 times greater than 10, and were able to produce higher molecular weight polymers than 10 or the commercial Dow CGC.
This document describes the synthesis of a novel thiol-functionalized poly(3-caprolactone) (PCL-HDT) using a two-step procedure. PCL-HDT is then used to prepare degradable elastomeric materials through either redox or thiol-ene cross-linking reactions. The resulting elastomers (EMSS from redox, EMTE from thiol-ene) exhibit improved mechanical properties and stability at body temperature. Furthermore, the reversibility of disulfide bond formation in EMSS confirms the potential of these materials for use as biodegradable elastomers in biomaterials applications.
Thermally Stimulated Discharge Current study of PMMA:PVP blendsinventionjournals
International Journal of Pharmaceutical Science Invention (IJPSI) is an international journal intended for professionals and researchers in all fields of Pahrmaceutical Science. IJPSI publishes research articles and reviews within the whole field Pharmacy and Pharmaceutical Science, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
This document describes research into creating a pH-sensitive poly(acrylamide-co-itaconic acid)/graphite composite hydrogel with conductive properties. The composite is prepared via free radical polymerization of acrylamide and itaconic acid monomers in the presence of settled graphite particles. SEM analysis shows uniform distribution of graphite in the polymer matrix. Conductivity increases then decreases with the amount of crosslinker and monomers used. Conductivity is also affected by the concentrations of itaconic acid and acrylamide in the reaction mixture. The composite shows promise for applications requiring electrically conductive materials.
The document summarizes research investigating the interface phenomena of poly(o-ethoxyaniline) (POEA) films using atomic force spectroscopy. The study found that POEA films consist of conducting islands surrounded by a less conductive matrix. The conducting islands were characterized by the presence of double-layer forces and visualized using transmission electron microscopy. The conducting islands were only 15 nm in diameter and could only be identified using adhesion mapping, not contact mode atomic force microscopy which showed larger aggregates. The degree of doping and pH affected the morphology and interactions observed, with fully dedoped POEA at pH 5 and partially conducting polyaniline.
This document summarizes the preparation and characterization of polymer-coated iron oxide magnetic nanoparticles. The nanoparticles were prepared via a two-step process: 1) magnetite nanoparticles were synthesized by co-precipitation of iron salts and 2) the magnetite nanoparticles were coated with polymer using emulsion polymerization. Scanning electron microscopy showed the nanoparticles were generally spherical and less than 20 nm in size. Fourier transform infrared spectroscopy confirmed the presence of the polymer coating on the nanoparticles. The polymer-coated magnetic nanoparticles have potential for uses in biomedical applications due to their superparamagnetic properties and ability to be functionalized.
O documento discute o desempenho e estratégias da operadora TIM no Brasil. Apresenta dados mostrando o crescimento consistente da receita, base de usuários e EBITDA nos últimos anos. Também destaca os planos de investimento da empresa para ampliar a cobertura 4G e impulsionar o crescimento de receitas com dados móveis.
The document discusses the challenges of mobile app development due to platform fragmentation. It notes that platform fragmentation increases costs and time-to-market due to the need to develop for multiple platforms and devices. It also introduces the Smartface platform as a solution that allows for cross-platform native mobile app development and management to address these challenges.
This document presents a study using density functional theory calculations to examine the adsorption of titanium dioxide nanostructures on pure and functionalized single-walled carbon nanotubes. The study finds that TiO2 nanostructures preferentially adsorb to chemical adsorption sites on functionalized SWCNTs, such as epoxy, alcohol, and carboxylate sites, compared to physical adsorption sites on pure SWCNTs, such as top, bridge, and hollow sites. Partial density of states calculations and charge density maps provide insight into the electronic structure and charge transfer between TiO2 nanostructures and SWCNTs. The results provide a theoretical understanding of controlled growth mechanisms of TiO2 nanostructures on carbon nanotube substrates.
Structural and Dielectric Properties of Lanthanum Substituted Lead ZirconateT...iosrjce
IOSR Journal of Applied Physics (IOSR-JAP) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
This study uses density functional theory calculations to examine the interaction between titanium oxide nanostructures and graphene or functionalized graphene nanoribbons (GNRs). The key findings are:
1) Rutile titanium dioxide favors physisorption on pure graphene, while rutile and anatase titanium dioxide show similar chemisorption on functionalized GNRs.
2) Charge density maps show the importance of electron distribution in the chemical interaction between titanium dioxide and graphene.
3) Analysis of partial density of states reveals the strength of binding energies at specific adsorption sites on the titanium dioxide/graphene systems.
4) The results provide insight into controlled growth mechanisms that could have applications in photovolta
Facile Synthesis and Characterization of Pyrolusite, β-MnO2, Nano Crystal wit...Editor IJCATR
MnO2 nanoparticles have been synthesized by a simple combustion method using MnSO4.4H2O. The crystalline phase, morphology, optical property and magnetic property of the as prepared nanoparticle were characterized using XRD, FT-IR, FT-Raman, SEM, UV-Vis, PL and VSM respectively. Structural studies by XRD indicate that the synthesized material as tetragonal rutile crystal structure. FT-IR and FT-Raman analysis revealed the stretching vibrations of metal ions in tetrahedral co-ordination confirming the crystal structure. The PL and UV analysis having an emission band at 390 nm, showed a prominent blue peak at 453 nm as well as a green emission lines at 553 nm with band gap energy of 3.2eV. Magnetic measurements indicate that the Néel temperature of the β-MnO2 structures is 92.5K for Hc = 100 Oe which showed antiferromagnetic behaviour.
A study the effect of zr o3 on the electrical and mechanical propertiesAlexander Decker
This document summarizes a study on the effect of adding ZrO3 on the electrical and mechanical properties of PMMA-Cr2O3 polymer composites. The study found that adding ZrO3 increased the electrical conductivity and ultrasound velocity of the composites. It also increased the relaxation amplitude, relaxation time, and bulk modulus while decreasing the molar conductivity, disintegration degree, and compressibility. The changes in properties are due to interactions between the polymer matrix and ZrO3 filler on the molecular level that affect ion motion and polymer chain structure. The addition of ZrO3 thus improves both the electrical and mechanical properties of the PMMA-Cr2O3 composite for applications.
International Journal of Research in Engineering and Science is an open access peer-reviewed international forum for scientists involved in research to publish quality and refereed papers. Papers reporting original research or experimentally proved review work are welcome. Papers for publication are selected through peer review to ensure originality, relevance, and readability.
This document summarizes the calculation of translational friction and intrinsic viscosity for four globular proteins (ribonuclease A, lysozyme, myoglobin, and chymotrypsinogen A) using their detailed atomic structures. The inclusion of a 0.9 Angstrom thick hydration shell around each protein allows the calculated translational friction and intrinsic viscosity to match experimental measurements. This hydration shell thickness corresponds to a hydration level of 0.3-0.4 grams of water per gram of protein, consistent with measurements from other techniques. Using detailed protein structures thus allows hydrodynamic measurements to support a unified picture of protein hydration, in contrast to earlier models that treated proteins as ellipsoids and found widely varying hydr
Electrodeposited pt on three dimensional interconnected graphene as a free st...tshankar20134
The document summarizes research on using a three-dimensional interconnected graphene structure as an electrode support for platinum nanoparticles for fuel cell applications. Key points:
1) Graphene was grown into a 3D foam-like structure using chemical vapor deposition on a nickel foam template, creating a seamless porous structure with high surface area and conductivity.
2) Platinum nanoparticles were deposited on the 3D graphene using pulsed electrodeposition, allowing control over particle size and uniform dispersion.
3) The 3D graphene with platinum nanoparticles showed improved catalytic activity for methanol oxidation compared to carbon fibers, due to the unique 3D structure, high surface area, and high conductivity of the graphene support.
Literature Seminar on Expansion of Pd chains through Beta-Carotene & Tetrapho...Nina Saraei
The document summarizes two papers on the expansion of palladium chains using β-carotene and tetraphosphine ligands. The first paper discusses the stepwise expansion of homonuclear and heteronuclear palladium chains from binuclear Pd(I) complexes supported by tetraphosphine ligands. Characterization data showed the complexes adopt linear structures with reversible metalation/demetalation. The second paper examines a bis-β-carotene ligand's ability to bind decanuclear palladium and palladium-platinum complexes into infinite π-stacked columns. Both papers demonstrate the use of multidentate ligands to control the assembly of extended metal atom chains.
This document summarizes research on the synthesis and characterization of nanobuilding blocks based on functionalized silsesquioxane cages. The researchers synthesized a series of [o-4-RStyrPhSiO1.5] cages of different sizes and degrees of functionalization via Heck coupling reactions. They characterized the compounds using various analytical techniques and studied their photophysical properties, including absorption, emission, and two-photon absorption. Unexpected photophysical behaviors were observed that depended on the functional group, cage geometry and degree of substitution. Density functional theory modeling supported the hypothesis that asymmetric bromination during synthesis led to asymmetrically functionalized cages with unusual polarization effects, explaining the observed photophysical properties.
Abstract
A small set of amphetamines has been analyzed by gas chromatography (GC) high-resolution time-of-flight mass spectrometry (TOFMS) using a microplasma photoionization (MPPI) soft-ionization source. This plasma-based, wavelength selectable ionization source enables ionization of the test compounds and their corresponding derivatives at ~8-12 eV that is a softer alternative to electron ionization at 70 eV. Three plasma gases were used in this study: Xe plasma that emits photons at resonance lines of 9.57 eV and 8.44 eV; Kr plasma at 10.63 eV and 10.02 eV, and Ar plasma at 11.82 eV and 11.61 eV. Derivatization of the test compounds with trifluoroacetic anhydride and α-methoxy-α-(trifluoromethyl)-phenylacetyl pyrazole was evaluated because the MPPI mass spectra of the underivatized amphetamines yield primarily iminium ions, which make the identification of the test compounds by GC-TOFMS inconclusive. The MPPI mass spectra of the TFA-derivatized amphetamines yield abundant molecular ions, when using Xe as plasma gas, and enough fragment ions with the Ar plasma that can help in formula generation. The structure elucidation of two "known unknowns" designer drugs using this "tunable" soft-ionization source and a high-resolution TOF mass spectrometer is presented in this study.
A facile route for nitrogen doped hollow graphitic carbonumarkhalid532
1) A facile route is presented for synthesizing nitrogen-doped hollow graphitic carbon spheres (NHGCSs) through the direct pyrolysis of solid melamine–formaldehyde (MF) resin spheres.
2) The MF resin spheres are prepared via a hydrothermal method without templates or catalysts, and pyrolyzed at temperatures above 400°C to form hollow carbon spheres with graphitic carbon shells.
3) The NHGCSs exhibit excellent capacitive performance as electrode materials for supercapacitors, achieving a high specific capacitance of 306 Fg-1 at 0.1 A g-1.
The document reports on research into the E. coli protein CusF. Key findings include:
1) The crystal structure of CusF bound to Ag(I) was determined to 1.0 angstrom resolution, revealing Ag(I) is coordinated by methionines M47 and M49 and histidine H36 in a beta barrel structure similar to the apo structure.
2) EXAFS was used to study CusF bound to Cu(I) since crystals could not be grown, showing Cu(I) is in a three-coordinate environment involving the same ligands.
3) Together the structures provide insight into how CusF sequesters toxic Cu(I) and Ag
This document describes a study investigating the effect of bridge length in new dinuclear constrained geometry catalysts (DCGCs) on the copolymerization behaviors of ethylene and styrene. Three new DCGCs were synthesized with bridge lengths of para-phenyl (10), para-xylyl (11), and para-diethylenephenyl (12). Copolymerization tests showed that catalyst activity, molecular weight of the copolymers, and styrene content all increased with increasing bridge length. Specifically, catalysts 11 and 12 showed activities 4-5 times greater than 10, and were able to produce higher molecular weight polymers than 10 or the commercial Dow CGC.
This document describes the synthesis of a novel thiol-functionalized poly(3-caprolactone) (PCL-HDT) using a two-step procedure. PCL-HDT is then used to prepare degradable elastomeric materials through either redox or thiol-ene cross-linking reactions. The resulting elastomers (EMSS from redox, EMTE from thiol-ene) exhibit improved mechanical properties and stability at body temperature. Furthermore, the reversibility of disulfide bond formation in EMSS confirms the potential of these materials for use as biodegradable elastomers in biomaterials applications.
Thermally Stimulated Discharge Current study of PMMA:PVP blendsinventionjournals
International Journal of Pharmaceutical Science Invention (IJPSI) is an international journal intended for professionals and researchers in all fields of Pahrmaceutical Science. IJPSI publishes research articles and reviews within the whole field Pharmacy and Pharmaceutical Science, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
This document describes research into creating a pH-sensitive poly(acrylamide-co-itaconic acid)/graphite composite hydrogel with conductive properties. The composite is prepared via free radical polymerization of acrylamide and itaconic acid monomers in the presence of settled graphite particles. SEM analysis shows uniform distribution of graphite in the polymer matrix. Conductivity increases then decreases with the amount of crosslinker and monomers used. Conductivity is also affected by the concentrations of itaconic acid and acrylamide in the reaction mixture. The composite shows promise for applications requiring electrically conductive materials.
The document summarizes research investigating the interface phenomena of poly(o-ethoxyaniline) (POEA) films using atomic force spectroscopy. The study found that POEA films consist of conducting islands surrounded by a less conductive matrix. The conducting islands were characterized by the presence of double-layer forces and visualized using transmission electron microscopy. The conducting islands were only 15 nm in diameter and could only be identified using adhesion mapping, not contact mode atomic force microscopy which showed larger aggregates. The degree of doping and pH affected the morphology and interactions observed, with fully dedoped POEA at pH 5 and partially conducting polyaniline.
This document summarizes the preparation and characterization of polymer-coated iron oxide magnetic nanoparticles. The nanoparticles were prepared via a two-step process: 1) magnetite nanoparticles were synthesized by co-precipitation of iron salts and 2) the magnetite nanoparticles were coated with polymer using emulsion polymerization. Scanning electron microscopy showed the nanoparticles were generally spherical and less than 20 nm in size. Fourier transform infrared spectroscopy confirmed the presence of the polymer coating on the nanoparticles. The polymer-coated magnetic nanoparticles have potential for uses in biomedical applications due to their superparamagnetic properties and ability to be functionalized.
O documento discute o desempenho e estratégias da operadora TIM no Brasil. Apresenta dados mostrando o crescimento consistente da receita, base de usuários e EBITDA nos últimos anos. Também destaca os planos de investimento da empresa para ampliar a cobertura 4G e impulsionar o crescimento de receitas com dados móveis.
The document discusses the challenges of mobile app development due to platform fragmentation. It notes that platform fragmentation increases costs and time-to-market due to the need to develop for multiple platforms and devices. It also introduces the Smartface platform as a solution that allows for cross-platform native mobile app development and management to address these challenges.
1) O município de Guarujá comemora o Dia Nacional do Livro Infantil com diversas atividades para incentivar a leitura entre crianças, como contação de histórias e exposições sobre o tema.
2) As bibliotecas municipais organizam programações especiais com o objetivo de estimular o hábito da leitura nos estudantes e homenagear o escritor Monteiro Lobato.
3) Atividades como entrega de carteirinhas de biblioteca e exposição sobre o Dia do Livro Infantil aconte
A arte colonial brasileira surgiu com a chegada dos portugueses no século XVI e foi influenciada pelos estilos barroco e rococó europeus. A arquitetura colonial se caracterizou principalmente por igrejas e fortalezas construídas de acordo com a função religiosa ou militar, com fachadas brancas e elementos simétricos. A arquitetura civil era mais simples, com casas de taipa de pilão e telhados de palha.
This document provides an overview of Colliers International's presence and real estate market forecasts across various Asia Pacific markets. It lists Colliers offices and contacts in over 30 cities across Asia, Australia, New Zealand, and India. For each market, it forecasts prime office rental rates, vacancy rates, and new supply for 2016-2017, indicating expected directional changes with up or down arrows. Real estate markets across the region are expected to see varied performance, with most major markets forecast to see rental rate increases but vacancy rate decreases.
Is Agile Data Science just two buzzwords put together? I argue that agile is a very practical and applicable methodology, that does work well in the real world for all sorts of Analytics and Data Science workflows.
http://theinnovationenterprise.com/summits/digital-web-analytics-summit-london-2015/schedule
The document summarizes recent research on new electro-optic properties of polysiloxane liquid crystal polymers. A series of polysiloxane-based side-chain liquid crystal polymers were prepared with systematic variation in spacer length between the mesogenic units and the polymer backbone. Electro-optic measurements showed that threshold voltage decreased with increasing spacer length. This was attributed to changes in intrinsic curvature elasticity rather than orientational order. Threshold voltage also decreased with increasing temperature and orientational order parameter. The results were consistent with existing models of curvature deformation in liquid crystals and provided insight into the effects of constraints from coupling mesogenic units to the polymer backbone.
This document reports on the synthesis, molecular structure, spectroscopic characterization, and quantum chemical calculation of (2E)-1-(5-chlorothiophen-2-yl)-3-(2,3,4-trimethoxyphenyl)prop-2-en-1-one. Single crystal X-ray diffraction, FT-IR, FT-Raman, and UV–vis spectra were recorded experimentally and compared to calculations. Density functional theory was used to optimize geometry, calculate vibrational frequencies, and predict structural and spectroscopic parameters. Natural bond orbital analysis was performed to analyze stability, hyperconjugation, and charge delocalization. Time-dependent density functional theory was used to calculate electronic transitions, absorption wavelengths, and frontier
This document reports on a study of the molecular structure, vibrational spectra, and electronic properties of (E)-N0-(4-Methoxybenzylidene)pyridine-3-carbohydrazide dihydrate (MBP3CDÁ2H2O) using density functional theory calculations and experimental techniques. The authors synthesized the compound and characterized it using FTIR, FT-Raman, and UV–Vis spectroscopy. They then used DFT calculations to optimize the molecular geometry, simulate the vibrational spectra, and analyze properties like hyperpolarizability. The calculated spectra agreed well with experimental data. Analysis of molecular orbitals, reactivity, and thermodynamics provided insight into
In this paper, the analysis of optically responsive microfibers with uniaxially ordered liquid crystal (LC) molecules at their cores is discussed. LC microfibers were electrospun from a solution of poly(vinyl pyrrolidone) (PVP) and N-(4-methoxybenzylidene)-4$-butylaniline (MBBA) using absolute alcohol as a solvent. Two parallel copper (Cu) collectors were used to obtain ordered fibers. The microfibers with oriented LC molecules were well fabricated at a voltage of 5 kV. A thermal-optical analysis revealed that the fibers were responsive to temperature. The rise of temperature from nematic to isotropic phase of LC decreased the LC intensity under a polarized optical microscope (POM).
This document summarizes research on a series of siloxane-based side chain liquid crystal polymers where the length of the coupling chain between the mesogenic unit and polymer backbone was systematically varied. All polymers exhibited a smectic phase and the nematic-isotropic transition temperature increased with longer coupling chain length. Electro-optic measurements found that threshold voltage for reorientation decreased with increasing chain length due to changes in intrinsic curvature elasticity rather than orientational order. A model is presented where constraints from coupling the mesogenic units to the backbone influence the observed electric-optic properties as chain length varies.
A series of siloxane based side chain liquid crystal polymers have been prepared with asystematic variation in spacer length. Nematic liquid crystal polymers possess large optical nonlinearities owing to their large refractive index anisotropy coupled with the collective molecular reorientation. All the polymer exhibited a smectic phase, for which the Nematic -isotropic transition temperature increased as the spacer length increased. Electro-optic measurements are used to evaluate the threshold voltages for this series of polymers. It is found that with increasing spacer length (n) of polymer the threshold voltage is lowered and that the variation of the threshold voltage arises from changes to the intrinsic curvature elasticity rather than to differences in orientational order. A simple model is used to indicate the origion of the effects observed which appear to arise from the constraints offered by the coupling of the mesogenic units to the polymer backbone.
This document discusses a study on the effect of coupling chain length on the electro-optic properties of siloxane-based side chain liquid crystal polymers.
A series of polymers were prepared with systematic variation in the length of the spacer (coupling chain) between the mesogenic unit and polymer backbone. All polymers exhibited a smectic phase, with the nematic-isotropic transition temperature increasing with spacer length.
Electro-optic measurements were used to evaluate threshold voltages. It was found that threshold voltage decreased with increasing spacer length. This suggests the variation in threshold voltage arises from changes to the intrinsic curvature elasticity rather than orientational order.
A simple model indicates the effects observed may arise from constraints of
This document summarizes research on a series of siloxane-based side chain liquid crystal polymers where the length of the coupling chain between the mesogenic unit and polymer backbone was systematically varied. All polymers exhibited a smectic phase and the nematic-isotropic transition temperature increased with longer coupling chain length. Electro-optic measurements found that threshold voltage for reorientation decreased with increasing chain length due to changes in intrinsic curvature elasticity rather than orientational order. A model is presented where constraints from coupling the mesogenic units to the backbone influence the observed effects, which appear to depend on coupling chain length.
The document discusses perovskite solar cells. It begins by defining perovskites and their crystal structure. It then discusses several important studies on perovskite solar cells that improved their efficiency over time, including studies published in 2012, 2013, 2014 and 2015 that achieved efficiencies up to 19.3%. It also reviews factors that affect the performance and stability of perovskite solar cells, such as humidity, UV light, annealing temperature, and the choice of electron transport material. In conclusion, it summarizes that perovskite solar cells have advantages over traditional silicon solar cells like easier processing, higher efficiency potential, flexibility and lower cost.
CH3NH3PbCl3 Single Crystals Inverse Temperature Crystallizati.docxcravennichole326
CH3NH3PbCl3 Single Crystals: Inverse Temperature Crystallization
and Visible-Blind UV-Photodetector
Giacomo Maculan,†,∥ Arif D. Sheikh,‡,∥ Ahmed L. Abdelhady,†,§ Makhsud I. Saidaminov,†
Md Azimul Haque,‡ Banavoth Murali,† Erkki Alarousu,† Omar F. Mohammed,† Tom Wu,*,‡
and Osman M. Bakr*,†
†Division of Physical Sciences and Engineering, Solar and Photovoltaics Engineering Research Center, King Abdullah University of
Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia
‡Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom
of Saudi Arabia
§Department of Chemistry, Faculty of Science, Mansoura University, Mansoura, 35516, Egypt
*S Supporting Information
ABSTRACT: Single crystals of hybrid perovskites have shown remarkably improved
physical properties compared to their polycrystalline film counterparts, underscoring their
importance in the further development of advanced semiconductor devices. Here we
present a new method of growing sizable CH3NH3PbCl3 single crystals based on the
retrograde solubility behavior of hybrid perovskites. We show, for the first time, the energy
band structure, charge recombination, and transport properties of CH3NH3PbCl3 single
crystals. These crystals exhibit trap-state density, charge carrier concentration, mobility,
and diffusion length comparable with the best quality crystals of methylammonium lead
iodide or bromide perovskites reported so far. The high quality of the crystal along with its
suitable optical band gap enabled us to build an efficient visible-blind UV-photodetector,
demonstrating its potential in optoelectronic applications.
In the past few years, organo-lead halide perovskites MAPbX3(MA = CH3NH3+, X = Cl−, Br−, or I−) have drawn the
attention of many scientists due to their attractive optical and
electrical properties, together with their moderate cost and low-
temperature solution-processability.1−7 These merits make
them one of the most promising candidates for the industrial
development of next-generation optoelectronic devices. In
particular, MAPbI3 and MAPbBr3 showed strong optical
absorption coefficients across the visible spectra,8 combined
with balanced and long-range electron−hole diffusion lengths9
and low trap-state densities,10,11 resulting in broad employment
of these materials in high efficiency solar cells,12−17 light
emitting diodes,18,19 lasers20,21 and photodetectors.22−24
Optical and electrical studies conducted on single crystals of
organo-lead bromide and iodide perovskites11,25 revealed that
the properties are considerably enhanced in single crystals,
compared to their polycrystalline thin film counterparts. This
property enhancement is reflected by the absence of an
absorption peak near the band gap of the crystals, which
indicates more order and long-range structure.11 Moreover,
charge carrier lifetimes in single crystals are longer due to a
lower trap-induced recombination rate ...
2015 New trans-stilbene derivatives with large TPA valuesvarun Kundi
This document discusses a theoretical study of the linear and non-linear optical properties of 13 new trans-stilbene derivatives designed to have large two-photon absorption cross-sections. The study uses density functional theory and time-dependent density functional theory calculations with the CAM-B3LYP functional to evaluate properties like hyperpolarizability and one- and two-photon absorption. It finds that derivatives TSBD-10, TSBD-11, TSBD-12, and TSBD-13 have particularly large non-linear optical susceptibilities and two-photon absorption cross-sections, with the largest being 5560 GM for TSBD-13.
This document characterizes cellulose nanocrystals grafted with organic acid chlorides of different sizes. The nanocrystals were obtained from ramie fibers through acid hydrolysis and then chemically modified through grafting with hexanoyl chloride, lauroyl chloride, and stearoyl chloride. Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy were used to characterize the morphology, crystallinity, and occurrence of chemical modification. The objective of the surface chemical treatment was to enhance the nonpolar nature and improve dispersibility of the nanocrystals in nonpolar polymeric matrices.
Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Co...Pawan Kumar
We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low-band-gap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J–V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core–shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.
This document summarizes the fabrication of surface-confined heterometallic molecular triads (SURHMTs) on solid substrates. SURHMTs were fabricated using terpyridyl complexes of Fe, Os, and Ru as metalloligands and Cu2+ ions as linkers. Optical and electrochemical studies showed efficient electronic communication within the triads. The triads exhibited a combination of optical bands from the individual complexes and multiple redox peaks. One triad was investigated for use in molecular logic gates based on its interaction with a redox-active molecule.
Equivalent Dielectric property of hydrogenated carbon nitride film in CH4/N2 ...inventionjournals
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
This study investigated the effects of UV light intensity on the dielectric properties of a cholesteric liquid crystal (CLC) composite containing a nematic liquid crystal and a chiral additive, with and without the addition of 2% methyl red (MR) azo dye. Dielectric measurements were performed on the samples under various UV light intensities (0-90 mW/cm2) and voltages (0 V and 40 V). The results showed that the dielectric constant increased with UV light intensity at low frequencies. The relaxation frequency also increased with UV light exposure. The CLC sample exhibited a transition in dielectric anisotropy but this disappeared for the dye-doped composite at higher UV intensities. Conductivity properties increased with the addition of MR and
The document summarizes a study that investigated how the photoluminescence quantum yield of lead selenide quantum dots is affected by increasing excitation energy. Three samples of PbSe quantum dots were synthesized with different diameters and characterized. It was found that the quantum yield decreased as the excitation energy increased, likely due to the formation of multi-exciton states within single quantum dots that lead to non-radiative Auger processes. The quantum yield was measured using an integrating sphere method and by analyzing absorption and emission spectra of the samples excited at different wavelengths. The results supported the expectation that higher excitation energies reduce quantum yield.
Role of αc–relaxation in high-temperature polymer deformation.
Proceedings of the American Society for Composites 2009-Twenty-Fourth Technical ConferenceWith the Canadian Association for Composite Structures and Materials (Joint Canadian-American International Conference), September 15-17, Newark, DE
Provides up to date information on DSC, recent developments and applicability. Recommended for those seeking up-to-date information on thermal analysis instruments.
A facile method to prepare CdO-Mn3O4 nanocompositeIOSR Journals
CdO-Mn3O4 nanocomposite has been prepared by a simple solvothermal method using a domestic microwave oven. Cadmium acetate, manganese acetate and urea were used as the precursors and ethylene glycol as the solvent. The as-prepared sample was annealed for 1 hour in each case at different temperatures, viz. 100, 200 and 300°C. The as-prepared and annealed samples were characterized by X-ray diffraction and scanning electron microscopic analyses. Results indicate that annealing at 300°C is required to get the sample with high phase purity and homogeneity. The present study indicates that the method adopted can be considered as an economical and scalable one to prepare the proposed nanocomposite with reduced size, phase purity and homogeneity.
2. functional materials demand combination of these unusual
features.24,25
Hence, in this work, three-ring-based thermo-
tropic mesogens with terminal N,N-dimethylamino moiety and
alkoxy chain are synthesized and a comprehensive character-
ization is attempted using hot-stage optical polarizing
microscopy (HOPM), differential scanning calorimetry
(DSC), and single-crystal as well as powder X-ray diffraction
(XRD) to realize the liquid crystalline properties and the
molecular packing. Quite interestingly for a dodecyloxy
mesogen, the XRD result suggests an interdigitated smectic
layer organization which is a rare feature in N,N-dimethylami-
no-based mesogens. Furthermore, density functional theory
(DFT) calculations are used to determing the geometry-
optimized structure, highest occupied molecular orbital−lowest
unoccupied molecular orbital (HOMO−LUMO) properties as
well as 13
C NMR isotropic chemical shifts. Additionally, the
photophysical properties of the C12 homologue is explored by
performing steady-state as well as time-resolved fluorescence
measurements.26,27
In recent years, the solid-state 13
C NMR
experiments, specifically, the two-dimensional (2D) separated
local field (SLF) measurements in liquid crystalline phase have
become popular in view of the wealth of information viz. the
molecular order, molecular topology, and molecular dynamics
offered by the technique.28−32
Hence, the 2D SAMPI-4
experiments are also accomplished for determining the
orientational order for a representative C12 mesogen in SmAd
and nematic phases.
■ EXPERIMENTAL SECTION
The compounds, namely, 4-(((4-(hexyloxy)phenyl)imino)-
methyl)phenyl benzoate (HIMPDB), 4-(((4-dodecyloxy-
phenyl)imino)methyl)phenyl4-(dimethylamino)benzoate
(DdIMPDB), and 4-(((4-(dodecyloxy)phenyl)imino)methyl)-
phenyl benzoate (DdPPB) were synthesized by multistep
synthetic routes. The experimental protocols and the spectral
data are provided in Supporting Information.
Instrumentation Details. Fourier transform infrared (FT-
IR) spectra of the compounds were recorded on an ABB
BOMEM MB3000 spectrometer using KBr pellets. 1
H and 13
C
solution NMR spectra of the mesogens in CDCl3 were acquired
on a Bruker 400 MHz Avance III HD NanoBay NMR
spectrometer. Typically, 0.5 mg of the sample was dissolved in
0.7 mL CDCl3 at room temperature, and tetramethylsilane
(TMS) was used as the internal standard. The resonance
frequencies of 1
H and 13
C were 400.23 and 100.64 MHz,
respectively. The nature of the mesophase and the temperature
of occurrence were determined with an Olympus BX50 hot-
stage optical polarizing microscope equipped with Linkam
THMS 600 stage and TMS 94 temperature controller. The
photographs were taken using an Olympus C7070 digital
camera. Differential scanning calorimetry traces were recorded
using a DSC Q200 instrument with a heating rate of 10 °C/min
in nitrogen atmosphere. The data obtained from the second
heating is considered for discussion. The single-crystal X-ray
structure of HIMPDB was determined using a Bruker Kappa
APEXII single-crystal X-ray diffractometer at SAIF, IIT-Madras,
Chennai. UV−visible absorption spectra were measured using a
Shimadzu UV-1800 spectrophotometer. The steady-state
fluorescence measurements were carried out by a Varian Cary
Eclipse fluorescence spectrophotometer, whereas the fluores-
cence lifetime decay profiles were measured by the time-
correlated single photon counting method (IBH). The samples
were excited at 375 nm laser (Tsunami, Spectra Physics), and
the decay curves were monitored at respective emission
maximum wavelength. The decay profiles were analyzed using
DAS6 software and are fitted satisfactorily with a single
exponential function.
Computational Details. The ground (S0) geometries of
DdIMPDB and DdPPB were optimized using a density
functional theory-based method with Becke’s three-parameter
functional and the Lee−Yang−Parr functional (B3LYP)33,34
with 6-31G* basis set. On the basis of the gas-phase optimized
geometry of DdIMPDB and DdPPB, spectral properties in
chloroform were calculated by time-dependent density func-
tional theory (TD-DFT) method with the polarizable
continuum model (PCM) at the B3LYP/6-31G* level of
theory. All the calculations were carried out using the Gaussian
09 program package.35
Powder X-ray Measurements. Powder X-ray diffraction
studies of the unoriented samples (Lindemann capillary;
diameter of 1 mm; Hampton Research, Aliso Viejo, CA)
were carried out using a PANalytical instrument (DY 1042-
Empyrean) operating with a line focused Ni-filtered Cu Kα (λ
= 1.54 Å) beam and a linear detector (PIXcel 3D). The sample
temperature was controlled with a precision of 0.1 °C using a
heater and a temperature controller (Linkam).36,37
Solid-State NMR Measurements. The solid-state NMR
experiments were carried out on a Bruker Avance III HD 400
WB NMR spectrometer (9.4 T). 1
H and 13
C resonance
frequencies were 400.07 and 100.61 MHz, respectively. The
spectra in the liquid crystalline phases of the sample were
recorded using a double-resonance 4 mm MAS WVT probe
under static conditions. Because the liquid crystalline phase is
observed at higher temperature for DdIMPDB, the sample is a
fine powder at room temperature. Typically, 100 mg of the
powder sample was taken in a 4 mm Zirconia rotor with Teflon
spacer. The sample alignment was achieved by first heating to
the isotropic phase and then slowly cooling to the respective
mesophases. The 1D 13
C NMR spectra in SmAd and nematic
phases were obtained by cross-polarization (CP) scheme with a
contact time of 3 ms; number of scans, 256; recycle delay, 8 s;
and 62.5 kHz radio frequency (RF) field strength on both the
1
H and 13
C channels. High-resolution 2D SLF spectra were
obtained under static conditions using the SAMPI-4 pulse
sequence38
(Figure S6 of Supporting Information) that
correlates the 13
C chemical shift with the associated 13
C−1
H
dipolar coupling. Experimental conditions for SAMPI-4 pulse
scheme for liquid crystalline samples were described in our
earlier work.12,28,29,39
The CP contact time (τ) was 3 ms; the
number of t1 increments was 100, and the signal was acquired
with 28 transients for each t1 increment. To minimize RF
heating effects, a recycle delay of 15s was used. The data were
zero filled in both the t2 and t1 dimensions, yielding a 4096 ×
256 real matrix. A shifted sine bell window function was applied
to the time domain data, and the spectrum was processed in the
phase sensitive mode. In all the experiments, SPINAL-6440
with
30 kHz RF field strength was used to provide heteronuclear
decoupling during the carbon signal acquisition. The sample
temperature was regulated by a Bruker BVTB-3500 variable
temperature unit and assessed from 207
Pb NMR chemical shift
of Pb (NO3)2.41
The 13
C chemical shift was externally
referenced relative to the methine carbon of adamantane at
29.5 ppm.
The Journal of Physical Chemistry C Article
DOI: 10.1021/acs.jpcc.5b00630
J. Phys. Chem. C 2015, 119, 9477−9487
9478
3. ■ RESULTS AND DISCUSSION
Scheme 1 shows the synthetic strategy adopted for preparing
N,N-dimethylamino-based three-ring mesogens covered in this
work. Accordingly, the target mesogens are achieved by
condensing 4-N,N-dimethylaminobenzoyloxy benzaldehyde
and 4-alkoxyanilines in ethanol under microwave conditions.
The intermediate two-ring aldehyde is prepared by reacting 4-
N,N-dimethylamino benzoic acid with 4-hydroxy benzaldehyde
using DCC/DMAP in THF−DCM mixture at 0 °C.
Consequently, the phenyl rings of the core are connected
through ester and imine linking units while N,N-dimethylamino
and alkoxy chains are positioned at terminal locations. When
the length of the terminal alkoxy chain is varied from C2 to C12
(even number carbons only), six mesogens are prepared. Figure
1 shows the DdIMPDB planar structure along with carbon
numbers and the geometry-optimized structure from DFT. In
addition, the direction and magnitude of the dipole moment
(4.77 D) is shown for the geometry-optimized structure.
Additionally, DFT is employed for determining the 13
C
chemical shifts as well as examining the HOMO−LUMO
levels to understand the photophysical properties of
DdIMPDB. The 13
C NMR chemical shift values computed
from DFT are compared with solution 13
C NMR values to
complete the assignment of all the core unit carbons.
Furthermore, the overall length of the molecule (L) is found
to be 35.96 Å from the geometry-optimized structure. In
addition, the structural identity of all the synthesized mesogens
is established by FT-IR and 1
H and 13
C NMR spectral
techniques (Figure S1−S3 of Supporting Information).
Mesophase Transitions and Molecular Organization.
The liquid crystalline properties of the synthesized mesogens
were carried out by HOPM and DSC methods, which revealed
the occurrence of enantiotropic nematic phase for all the
mesogens and an additional SmAd phase for DdIMPDB. For
instance, in HOPM, upon cooling the samples from isotropic
phase, either schlieren texture or marble texture is seen for the
nematic phase whereasa fan texture is clearly noticed for the
SmAd mesophase (Figure 2).42
These observations are further
established by DSC in which typical transitions associated with
TC−N and TN−I are noticed for all the homologues (Figure S4 of
Supporting Information) (Table 1). For DdIMPDB, an
enantiotropic SmAd mesophase is additionally observed in
DSC scan (Figure 3). An examination of crystal-to-mesophase
transition temperatures (Table 1) reveal that with increase in
terminal chain length, a decrease in transition values is noticed,
although the trend is not uniform across the homologues. The
TN−I values, on the other hand, showed a regular decrease with
increase in terminal chain length.43
Accordingly, the mesophase
range for all the mesogens showed variation in the span of 60−
90 °C. The good mesophase range suggests that the anisotropic
molecular polarizability is high because of the presence of N,N-
dimethylamino group, which is in conjugation with phenyl rings
of the core unit.43,44
To ascertain the molecular packing and
geometry, the single-crystal structure of HIMPDB is
determined. The XRD data indicates triclinic, P1 space group
of the crystal structure with antiparallel packing (Figure 4b).
The important features of the single-crystal data are listed in
Table 2.
The powder X-ray diffraction of DdIMPDB in the temper-
ature range of 120−190 °C is accomplished because it exhibits
enantiotropic SmAd phase in addition to nematic phase. Table
3 lists the d values measured from powder X-ray diffraction at
Scheme 1
Figure 1. Molecular structure and energy-optimized space-filled model
showing magnitude and direction of dipole moment of DdIMPDB.
Figure 2. HOPM photographs of (a) nematic phase of BIMPDB at
250.1 °C, (b) nematic phase of HIMPDB at 228.8 °C, (c) nematic
phase of OIMPDB at 225.5 °C, and (d) SmAd phase of DdIMPDB at
170.8 °C.
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4. various temperatures in the smectic mesophase. The diffracto-
gram at 150 °C (Figure 5) shows a sharp reflection in the small-
angle region and a broad hump in the wide-angle region. The
presence of sharp reflection in the small-angle region is
characteristic of layer ordering of smectic phase while the broad
hump in the wide-angle region indicates the absence of in-plane
order and liquidlike nature of molecules in the layer (Figure
5).45−47
Accordingly, the layer spacing, d, is found to be 53.44
Å at 150 °C. Table 3 lists the d/L ratio, where L is the length of
the geometry-optimized DdIMPDB mesogen and d is the layer
spacing measured from the diffractogram at various temper-
atures. It is clear from Table 3 that the d/ L ratio in the
temperature range (120−190 °C) is found to be ∼1.46−1.51.
These values distinctly suggest that the smectic phase is
interdigitated bilayer smectic A type (SmAd).45−49
It is
remarkable to note that N,N-dimethylamino-based mesogens
usually show nematic phase.5,50
The presence of SmAd in
DdIMPDB is an interesting observation because such an
organization is normally encountered with mesogens possessing
terminal polar groups like CN, NO2, etc.20−23,45−49
In contrast,
Table 1. Transition Temperatures and Enthalpy Values of Synthesized Mesogens (4a−f)
code temperature TC−N/C−SmAd ΔH (K·cal/mol) temperature TSmAd−N ΔH (K·cal/mol) ΔT TSmAd−N temperature TN−I ΔH (K·cal/mol) ΔT TN−I
4a 182.7 7.28 − − − 255.6 0.33 66.7
4b 169.6 6.81 − − − 251.8 0.38 76.2
4c 148.7 6.84 − − − 236.7 0.31 88.0
4d 126.9 8.43 − − − 222.9 0.29 96.0
4e 133.2 9.06 − − − 211.9 0.22 78.7
4f 122.8 8.35 178.1 0.0096 53.3 209.5 0.18 31.4
Figure 3. DSC second heating and cooling scans of DdIMPDB.
Figure 4. (a) ORTEP diagram of HIMPDB; (b) antiparallel packing of HIMPDB in crystal.
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5. in DdIMPDB, finding SmAd phase with an electron-releasing
N,N-dimethylamino group at the terminal position is a
significant observation. Furthermore, it is generally noticed
that in SmAd, the molecules are preferred to be in antiparallel
packing to compensate the net polarity.20−23
It is important to
note that the single-crystal structure of HIMPDB, a C6
homologue, also shows antiparallel packing. Thus, it is quite
likely that when DdIMPDB melts into smectic mesophase the
antiparallel organization is preserved, as experimentally
confirmed by XRD measurements.
Photophysical Properties in Solution. It has been
established based on the photophysical studies that N,N-
dimethylamino benzoates exhibit twisted intramolecular charge-
transfer (TICT) interactions.26,27,51,52
Because the mesogens
under investigation are constructed from 4-dimethylamino
benzoic acid, the photophysical properties of DdIMPDB in
different solvents are investigated using steady-state and time-
resolved fluorescence techniques.53,54
Quite interestingly, the
UV−visible absorption spectra of DdIMPDB (Figure 6)
remains insensitive to the solvent polarity, whereas the
fluorescence maxima are found to be fairly sensitive to the
solvent polarity (Figure 7). Indeed, the fluorescence maximum
of DdIMPDB is found to be 480, 498, 475, 408, and 447 nm in
chloroform, dichloromethane, tetrahydrofuran, acetonitrile and
N,N-dimethyl sulfoxide solvents, respectively. This phenomen-
on is quite intriguing as the fluorescence maxima becomes blue-
shifted with increase in solvent polarity which, is in sharp
contrast to the behavior generally observed for N,N-
dimethylaminobenzoates.55
The negative solvatochromism in
fluorescence witnessed for DdIMPDB is a rare observation, and
most of the probes known to date exhibit negative
solvatochromism in absorption rather than fluorescence. The
Table 2. Single-Crystal Data of HIMPDB
empirical formula C28H32N2O3
formula weight 444.56
crystal system triclinic
crystal size (mm) 0.35 × 0.35 × 0.30
space group P1
a (Å) 9.6360(3)
b (Å) 10.8458(3)
c (Å) 12.5627(4)
α (Å) 100.934(2)
β (Å) 97.887(2)
γ (Å) 109.429(2)
V (Å3
) 1186.90(6)
Z 2
ρcalcd (g cm−3
) 1.244
F(000) 476
temperature (K) 293(2)
radiation MoKα λ (Å) 0.71073
goodness-of-fit on F2
1.020
reflections collected/unique 20470/4188
data/restraints/parameters 4188/0/299
R (int) 0.0310
CCDC entry, 1044591
Table 3. Powder X-ray Diffraction Data of DdIMPDB
temperature (°C) d1 (Å) d2 (Å) d/L
190 52.61 4.65 1.46
170 52.60 4.63 1.46
160 53.44 4.62 1.48
150 53.44 4.60 1.48
140 53.44 4.59 1.48
130 54.30 4.56 1.51
120 54.30 4.53 1.51
Figure 5. Powder X-ray diffraction profile for DdIMPDB at 150 °C.
Figure 6. Solution absorption spectra of DdIMPDB in different
solvents.
Figure 7. Solution fluorescence spectra of DdIMPDB in different
solvents.
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6. Stokes shift value calculated from the lowest-energy absorption
and fluorescence maxima is 9750, 9690, 9900, 6460, and 7840
cm−1
in chloroform, dichloromethane, tetrahydrofuran, aceto-
nitrile, and N,N-dimethyl sulfoxide solvents, respectively. The
larger Stokes shift can be due to the significant structural
changes that occur between the ground and excited state and to
the intramolecular charge-transfer interactions. Nonetheless,
the fluorescence lifetime remains almost constant ca. 1.14 ± 0.2
ns irrespective of the solvent used. In view of these interesting
electronic properties of DdIMPDB, the nature of the electronic
transition and frontier molecular orbital (FMO) distributions
are investigated using density functional theory (DFT) at the
B3LYP/6-31G* level of theory. The calculated FMO
distributions of DdIMPDB are presented in Figure 8. It is
evident from Figure 8 that for DdIMPDB, both HOMO and
LUMO are localized on the benzylidene-phenyl unit. A close
examination of these orbitals reveals that the HOMO is
predominantly localized on the benzylidene-phenyl unit while
the LUMO is mostly concentrated on the phenyl benzoate
unit; N,N-dimethylaminobenzoate does not have any significant
influence on the HOMO and LUMO. Thus, it can be
concluded that the electronic properties of DdIMPDB could
have originated from the benzylidene-phenyl rather than the
N,N-dimethylaminobenzoate moiety. TD-DFT calculations
presented in Table 4 have close agreement with experimental
results. For the DdIMPDB, the maximum peak is predicted to
be at 320.6 nm (f = 1.2034) which arises from the HOMO →
LUMO+1 (47%) and HOMO−1 → LUMO (32%) transitions.
To get clear insights on the role of N,N-dimethylamino group
on electronic properties, the frontier molecular orbitals are also
calculated for a hypothetical molecule DdPPB in which the
terminal N,N-dimethylamino moiety is absent, wherein the
LUMO is localized on the phenyl benzoate unit (Figure 8). A
clear distinct feature in the LUMO for DdIMPDB and DdPPB
suggests that pronounced charge transfer can be seen for the
latter. The decrease in the magnitude of charge transfer in the
presence of N,N-dimethylamino group could be attributed to
its strong electron-donating behavior upon photoexcitation of
DdIMPDB, which can also be responsible for the negative
solvatochromism in fluorescence. The electron-transfer process
from the N,N-dimethylamino group to benzylidene-phenyl is
highly more favorable in polar solvents than the nonpolar
solvents. The facile electron-transfer process in the polar
environment probably destabilizes the excited state and leads to
the negative solvatochromism in fluorescence. To confirm this
hypothesis, the fluorescence spectra of DdPPB, which is a
structural analogue of DdIMPDB, without the terminal N,N-
dimethylamino group, is measured, which shows positive
solvatochromism in fluorescence (Figure S5 of Supporting
Information). On the basis of these facts, it can be concluded
that the electronic properties of the DdIMPDB molecule
originate from the benzylidene-phenyl moiety and the negative
solvatochromism is due to the photoinduced electron transfer
from dimethylamino group to benzylidene-phenyl of the core
unit.
Solid-State 13
C NMR Spectroscopy. One of the
synthesized mesogens, DdIMPDB, the C12 homologue, is
investigated by high-resolution solid-state 13
C NMR in SmAd
and nematic mesophases. The static 1D and 2D 13
C NMR
experiments are carried out in both phases with the purpose of
finding the orientational order. The core unit carbons in the
solution spectrum were assigned using 13
C chemical shifts
calculated by the DFT method. This is a useful starting point
for confirming the molecular structure and the assignment of
the carbon peaks in the liquid crystalline phase. Figure 9a shows
the proton decoupled 13
C NMR of DdIMPDB in CDCl3
measured at room temperature. For the three-ring core unit
carbons, 14 signals as listed in Table 5 are seen. For the
terminal units, the methyl of N,N-dimethylamino carbon is
noticed at 40 ppm and the methoxy carbon of dodecyloxy chain
is observed at 68.3 ppm. The other methylene carbons of the
terminal chain are seen in the range of 22−32 ppm, whereas
methyl carbon showed a distinct signal at 14.2 ppm. It is also
observed from the solution spectrum that the quaternary
carbons showed low intensity in contrast to phenyl ring
methine as well as imine methine carbons. The chemical shift
assigned to core unit carbons of the mesogen are listed in Table
5. Among all the core unit carbons, the imine carbon is
noticeable at 157 ppm. Thus, the solution 13
C NMR spectral
Figure 8. FMO distribution of DdIMPDB and DdPPB (isosurface value, 0.03 au) in CHCl3 at PCM-B 3LYP/6-31G* level of theory.
Table 4. Summary of the Excited-State Electronic Transitions Obtained from the TD-DFT Calculations at B3LYP/6-31G* Level
of Theory
compound solvent state absorption (nm) energy (eV) oscillator strength (f) dominant contribution (%)a
exptl. (nm)
DdIMPDB CHCl3 S1 320.6 3.87 1.2034 H → L+1 (47%), H-1 → L (32%) 328
S2 281.0 4.41 0.9054 H → L+1 (34%), H-1 → L (16%)
S3 205.2 6.04 0.2622 H → L+2 (32%), H-5 → L (32%)
DdPPB CHCl3 S1 320.5 3.87 0.9480 H → L (67%), H → L+1 (18%) 340
S2 266.3 4.66 0.6233 H-1 → L (38%),H-6 → L (28%)
a
H denotes HOMO and L denotes LUMO.
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7. features of DdIMPDB are very much consistent with the
molecular structure.
Panels b and c in Figure 9 show the static 13
C NMR spectra
of DdIMPDB in SmAd and nematic phases, respectively. The
high resolution of the spectrum as well as the 13
C chemical
shifts suggest the alignment of molecules in the magnetic field.
The chemical shift assignment of the spectral lines in the
mesophase is attempted by comparing the structurally similar
segments of known liquid crystals and also making use of the
2D SAMPI-4 spectrum (Figure 10). For instance, 4-alkoxy
benzylidene-based mesogens can provide the information about
the chemical shift values of ring II carbons.56
The assigned core
unit carbons along with alignment-induced chemical shifts
(AIS) are listed in Table 5. A clear increase in chemical shift
values of core unit carbons in contrast to solution spectrum is
noticed. For the terminal chain, a marginal decrease in chemical
shifts is noted in liquid crystalline phase as against the solution.
However, interestingly, for the N,N-dimethylamino carbons, an
increase in chemical shift value is noticed in contrast to solution
spectrum.57
This is in stark difference to dodecyloxy chain,
where decrease in chemical shifts of all the carbons is found in
mesophase in contrast to the solution spectrum. The increase
in chemical shift values of N,N-dimethylamino in the liquid
crystalline phase could be due to different orientation of methyl
group as against the terminal dodecyloxy chain. Because the
Figure 9. 13
C NMR spectra of DdIMPDB in (a) solution, (b) SmAd
phase at 145 °C, and (c) nematic phase at 195 °C.
Table 5. 13
C NMR Data of DdIMPDB in Solution and Liquid Crystalline States
145 °C 195 °C
C
no.
solution
(ppm)
DFT
(ppm)
SmAd phase
(ppm)
AIS
(ppm)
13
C−1
H dipolar oscillation
frequencies (kHz)
nematic phase
(ppm)
AIS
(ppm)
13
C−1
H dipolar oscillation
frequencies (kHz)
1 153.8 149.8 222.1 68.3 1.64 215.1 61.3 1.34
2 110.8 108.2 133.5 22.7 3.28 131.6 20.8 2.78
3 132.1 133.1 164.3 32.2 2.84 160.9 28.8 2.42
4 115.6 117.0 179.0 63.4 1.55 172.5 56.9 1.21
5 165.2 161.0 207.1 41.9 0.79 203.0 37.8 0.71
6 153.6 154.4 222.1 68.5 1.64 215.1 61.5 1.34
7 122.4 120.8 152.8 30.4 2.75 149.3 26.9 2.39
8 129.7 130.6 161.0 31.3 2.90 157.7 28.0 2.50
9 133.8 132.7 205.6 71.8 2.20 197.9 64.1 1.91
10 157.3 152.6 198.6 41.3 5.00 194.0 36.7 4.33
11 144.7 145.3 205.6 60.9 1.50 197.9 53.2 1.25
12 122.2 127.9 147.2 25.0 2.99 144.3 22.1 2.62
13 115.0 116.9 142.8 27.8 2.98 140.2 25.2 2.59
14 157.9 157.6 230.3 72.4 1.61 221.8 63.9 1.33
Figure 10. 2D SAMPI-4 spectra of DdIMPDB in (a) SmAd phase at
145 °C and (b) nematic phase at 195 °C.
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8. methyl groups of N,N-dimethylamino group are away from the
molecular axis, the orientation of the CSA tensors of methyl
carbon is different from that of the dodecyloxy methyl carbon.
Furthermore, in addition to 1D experiments, the 2D SLF
experiments are also carried out for DdIMPDB in SmAd and
nematic phases. The 2D spectrum measured at 145 °C in SmAd
phase (Figure 10a) shows as many as 12 contours with varying
intensities arising from protonated as well as nonprotonated
carbons. The 13
C−1
H dipolar couplings of the core unit are
listed in Table 5. The imine methine carbon showed a contour
at 194 ppm in nematic phase (Figure 10b) with a 13
C−1
H
dipolar coupling of 4.33 kHz. For the phenyl ring methine
carbons, the 13
C−1
H dipolar couplings are in the range of
∼2.39−3.78 kHz, whereas for the quaternary carbons, the
values are found to be ∼1.36−1.50 kHz. The 2D data also
provides support for the assignment of core unit as well as
terminal chain carbons because the separation of contours is
guided by the orientation of individual C−H vectors. For
instance, the identification of imine carbon is significantly easier
from the 2D spectrum than from the 1D data alone. Similarly,
the ester carbonyl assignment is straightforward because the
13
C−1
H dipolar coupling value would be less because it is away
from neighboring protonated carbons. Also, the assignment of
several methylene carbons of the dodecyloxy terminal chain in
2D is relatively easier than in the 1D spectrum (Figure 10). In
SmAd phase, the 13
C−1
H dipolar couplings as well as chemical
shifts showed an increase in contrast to nematic phase due to
increase in orientational order as SmAd is more ordered than
the nematic phase. The 13
C−1
H dipolar couplings (Table 5)
determined from 2D experiments in both phases are utilized for
finding the orientational order parameter.
The 2D SAMPI-4 provides dipolar oscillation frequencies
from which the dipolar couplings can be extracted by adopting
the established method.12,28,29,58,59
These 13
C−1
H dipolar
couplings are employed for finding the local orientational
order parameter of the phenyl rings by the following
equation.59−61
θ θ θ= − ′ + −
′ − ′
{
}
D K S
S S
1
2
(3cos 1)
1
2
(cos cos )
( )
z zz x y
xx yy
CH
2 2 2
(1)
where K = −hγHγC/4π2
rCH
3
; γH and γC are the gyromagnetic
ratios of protons and carbons, respectively; rCH is the
internuclear distance between the carbon and proton nuclei;
and θx, θy, and θz are angles that internuclear vector rCH forms
with the respective coordinate axes. The coordinate axes are the
local axes defined on the molecular fragment under
consideration; in this case, the phenyl ring is considered. The
z axis is the para axis of the phenyl ring and the x axis is
perpendicular and is in the plane of the ring. The standard
bond distances employed for the calculations are rCH = 1.1 Å
for the C−H bond and rCC = 1.4 Å for the C−C bond. During
the fitting procedure, the two C−C−H bond angles have been
slightly varied around 120° (assumed for an ideal hexagonal
geometry) in view of the uncertainty involved in the position of
the H atom as determined by X-rays.58
Thus, the calculated Szz′
and (Sxx′ − Syy′ ) for each phenyl ring of the core in SmAd and
nematic phase, respectively, are listed in Table 6. Accordingly,
Szz′ values of ring II in SmAd and nematic phases are 0.70 and
0.59, respectively. These values are comparable with those of
the calamitic mesogens that exhibit smectic A and nematic
phases which are reported in the literature.60−65
Based on the
order parameter values of three phenyl rings in both nematic
and SmAd phases, the location of the long axis passing through
the core can be identified. As explained in earlier work,46
the
ratios of order parameters of phenyl rings provide information
about the angles between phenyl rings of the core unit. It is
clear from Table 6 that in both phases, the order parameter of
ring II is higher than that of ring I as well as that of ring III.
This suggests that the long axis is more collinear to ring II than
the other two rings. In a recent study, Domenici et al.30
performed a 13
C NMR investigation of three-ring-based
mesogen with a chiral center that exhibits SA Devries phase
and SmC* phase and calculated the order parameters
employing 13
C chemical shifts as well as 13
C−1
H dipolar
couplings (PDLF). Using 13
C−1
H dipolar couplings in three
aromatic rings in SmA and in SmC* phases, the relative
orientation of rings have been determined. Interestingly, in
SmC* phase, the aromatic ring closer to the chiral lateral chain
is found to be much more tilted than the other two rings,
indicating the occurrence of a conformational change at the
SmA−SmC* phase transition. This observation is supported by
the order parameters which showed a decreasing trend in
Table 6. Planar Structure with Orienting Axis and Orientational Order Parameter Values of DdIMPDB
angles calculated dipolar oscillation frequencies (kHz)
T (°C) ring θb θc Szz′ Sxx′ − Syy′ b c a da
RMSD (kHz)
145 I 118.8 120.2 0.68 0.070 3.28 2.84 1.54 1.57 0.05
II 120.7 120.2 0.70 0.072 2.76 2.92 1.64 2.20 0.01
III 119.5 119.6 0.68 0.066 3.03 3.00 1.55 1.55 0.04
195 I 118.7 119.9 0.57 0.056 2.76 2.44 1.28 1.31 0.06
II 120.5 120.1 0.59 0.060 2.38 2.49 1.37 1.85 0.04
III 119.2 119.4 0.57 0.054 2.61 2.56 1.29 1.29 0.03
a
For carbon d in ring II, the contribution of the azomethine proton has also been taken into account.
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9. SmC*. However, in the present investigation, though the
mesogen exhibits SmAd, no evidence for conformational change
or anomaly in the order parameter values is noticed across the
transition from nematic to SmC* phase. Furthermore, a plot of
temperature and carbon chemical shifts (Figure S7 of
Supporting Information) of all the core unit carbons support
no abrupt change across the nematic-to-SmAd phase transition.
This suggests that the phase transition from nematic to SmAd is
not a first-order transition.66,67
This observation is very well
supported by the DSC data in which transition enthalpy
associated with nematic-to-SmAd phase is found to be low.
■ CONCLUSIONS
Thermotropic liquid crystals consisting of a three phenyl ring
core with dimethylamino moiety and alkoxy chain as terminal
units were synthesized from 4-N,N′-dimethylamino benzoic
acid. The HOPM and DSC measurements confirmed the
enantiotropic nematic mesophase for all the mesogens while
SmAd is additionally noticed for the C12 homologue. The XRD
studies revealed interdigitation of molecules in the layers of
SmA phase for the C12 homologue, wherein the d/L values
were found to be in the range of ∼1.46−1.51. Furthermore, the
photophysical properties of the C12 homologue in different
solvents revealed negative solvatochromism in fluorescence
emission. The DFT-based HOMO−LUMO calculations as well
as steady-state and time-resolved fluorescence studies indicated
intramolecular charge-transfer interactions. Additionally,
HOMO−LUMO calculations revealed that the electronic
properties of DdIMPDB originated from the benzylidene-
phenyl moiety and the negative solvatochromism was due to
the photoinduced electron transfer from dimethylamino group
to benzylidene-phenyl of the core unit. The temperature versus
13
C chemical shifts plot suggested that the phase transition
from nematic to SmAd is of a second-order nature, which was
well-supported by the ΔH values from the DSC measurements.
The 2D SLF NMR experiments enabled the determination of
the orientational order parameters in SmAd and nematic phases.
Based on the order parameter values of three phenyl rings in
both nematic and SmAd phases, the location of the long axis
passing through the core was identified. Furthermore, the
comprehensive characterization attempted in this investigation
indicates that the mesogens under investigation are eligible
candidates for organic light-emitting diode function. Thus, the
present investigation clearly revealed many interesting findings
such as appearance of SmAd mesophase, antiparallel packing of
molecules in crystal as well as smectic phase, negative
solvatochromism in solution, and the second-order nature of
the nematic-to-SmAd phase transition. Therefore, it appears
that the terminal dimethyamino group greatly influences many
properties in this class of mesogens, as supported by the
experimental data generated from a wide range of techniques.
■ ASSOCIATED CONTENT
*S Supporting Information
Synthesis details; FT-IR, 1
H NMR, and 13
C NMR spectral data
of intermediates and final mesogens; figure of SAMPI-4 pulse
sequence; DSC plot; fluorescence spectra; and plot of chemical
shifts versus temperature. This material is available free of
charge via the Internet at http://pubs.acs.org.
■ AUTHOR INFORMATION
Corresponding Author
*E-mail: tnswamy99@hotmail.com.
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
The authors thank Prof. K. V. Ramanathan, NMR Research
Centre, Indian Institute of Science, Bangalore, India for his
support and keen interest in this work. The authors are thankful
to Dr. V. Subramanian, CLRI, for the quantum chemical
calculations. M.G.R. and T.N. are grateful to Prof. V. A.
Raghunathan and Ms. K. N. Vasudha, Raman Research
Institute, Bangalore, India for the powder X-ray measurements.
We acknowledge the partial financial support from NWP-55,
and M.G.R. thanks Council of Scientific and Industrial Research
(CSIR), New Delhi for the financial support in the form of a
Senior Research Fellow.
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