This document summarizes a study on new electrically-driven chiral molecular switches based on axially dissymmetric 1,1'-binaphthyl and electrochromic viologens. The switches (R)-1 and (R)-2 were synthesized and characterized. Their optical properties, including absorption and circular dichroism spectra, changed drastically upon electrochemical redox reaction, demonstrating efficient chiroptical switching. The switches take advantage of the strong chirality of 1,1'-binaphthyl and the electrochromic behavior of viologens to achieve modulation of their chiroptical properties with an electric field.
1) Conjugated double bonds stabilize compounds through resonance and delocalization of pi electrons. This leads to increased stability and reactivity compared to isolated double bonds.
2) Allylic positions adjacent to double bonds exhibit increased reactivity due to stabilization of allylic radicals and cations by resonance. This leads to faster substitution and elimination reactions.
3) Conjugated systems undergo characteristic pericyclic reactions like the Diels-Alder reaction and electrocyclic reactions that involve concerted bonding changes across the pi system. These reactions allow for controlled synthesis of cyclic compounds.
Copper-Catalyzed Reactions with Diborons: From the Beginning to Recent ResultsHajime Ito
This document summarizes research from Hajime Ito's group at Hokkaido University on copper-catalyzed reactions with diborons. It describes early work in 2000 developing the first copper-catalyzed formal nucleophilic boration reaction using diboron reagents. This established a boryl-copper intermediate and the potential for ligand control of selectivity. Later work found that Xantphos ligand with copper gave high reactivity and selectivity in allylboron synthesis reactions. The group also developed the first asymmetric, copper-catalyzed allylboron synthesis using Xantphos ligand to achieve high enantioselectivity.
This document describes a new fluorescent sensor called DDS (dibenzimidazolo diimine sensor) that was designed and synthesized to selectively detect acetate ions. DDS exhibits a remarkable near-infrared emission through an excited state intramolecular proton transfer process. Upon addition of acetate ions, DDS solution changes color visibly from light yellow to pink under normal light. It also shows a large fluorescence enhancement in the near-infrared region, indicating selective detection of acetate ions over other competing anions. Density functional theory calculations help explain the selective binding and sensing mechanism of DDS for acetate ions.
The document discusses how changing the covalent radius of bonds in organic compounds can alter their properties. It presents that increasing the covalent radius will increase the distance between bonded atoms. This increased distance leads to lower melting points, boiling points, and tensile strength. The document constructs virtual models of organic compounds to demonstrate how compounds with the same structure but different covalent radii will have varying distances between atoms and altered properties as a result. It concludes that producing new properties in organic compounds can be achieved by modifying the covalent bond radius.
This document summarizes spectroscopic evidence from electronic absorption, magnetic circular dichroism (MCD), and resonance Raman spectroscopies that provide insight into the unique bonding interaction in oxo-molybdenum dithiolate complexes. The data suggests these complexes have low-energy sulfur to molybdenum charge transfer transitions originating from a set of four filled dithiolate orbitals that are primarily sulfur in character. Resonance Raman excitation profiles allowed assignment of an ene-dithiolate in-plane sulfur to molybdenum transition. Three totally symmetric vibrational modes were also identified. The results provide context for understanding electron transfer pathways in pyranopterin dithiolate centers
New Schiff base ligand (E)-6-(2-(4-
(dimethylamino)benzylideneamino)-2-phenylacetamido)-3,3-
dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic
acid = (HL) Figure(1) was prepared via condensation of
Ampicillin and 4(dimethylamino)benzaldehyde in methanol
.Polydentate mixed ligand complexes were obtained from 1:1:2
molar ratio reactions with metal ions and HL, 2NA on reaction
with MCl2 .nH2O salt yields complexes corresponding to the
formulas [M(L)(NA)2Cl] ,where M =
Fe(II),Co(II),Ni(II),Cu(II),and Zn(II) and NA=nicotinamide.
The 1H-NMR, FT-IR, UV-Vis and elemental analysis
were used for the characterization of the ligand. The complexes
were structurally studied through AAS, FT-IR, UV-Vis,
chloride contents, conductance, and magnetic susceptibility
measurements. All complexes are non-electrolytes in DMSO
solution. Octahedral geometries have been suggested for each
of the complexes. The Schiff base ligands function as
tridentates and the deprotonated enolic form is preferred for
coordination. In order to evaluate the effect of the bactericidal
activity, these synthesized complexes, in comparison to the un
complexed Schiff base has been screened against bacterial
species, Staphy
Schiff base is a compound formed by the condensation reaction of a carbonyl group with a primary amine. The document discusses various methods for preparing Schiff base ligands and complexes, and techniques for characterizing them including UV-visible spectroscopy, IR spectroscopy, NMR, EPR, mass spectrometry, TGA/DTA, and elemental analysis. Schiff base ligands and their complexes have applications in areas like biology, catalysis, materials science, and more.
1) Conjugated double bonds stabilize compounds through resonance and delocalization of pi electrons. This leads to increased stability and reactivity compared to isolated double bonds.
2) Allylic positions adjacent to double bonds exhibit increased reactivity due to stabilization of allylic radicals and cations by resonance. This leads to faster substitution and elimination reactions.
3) Conjugated systems undergo characteristic pericyclic reactions like the Diels-Alder reaction and electrocyclic reactions that involve concerted bonding changes across the pi system. These reactions allow for controlled synthesis of cyclic compounds.
Copper-Catalyzed Reactions with Diborons: From the Beginning to Recent ResultsHajime Ito
This document summarizes research from Hajime Ito's group at Hokkaido University on copper-catalyzed reactions with diborons. It describes early work in 2000 developing the first copper-catalyzed formal nucleophilic boration reaction using diboron reagents. This established a boryl-copper intermediate and the potential for ligand control of selectivity. Later work found that Xantphos ligand with copper gave high reactivity and selectivity in allylboron synthesis reactions. The group also developed the first asymmetric, copper-catalyzed allylboron synthesis using Xantphos ligand to achieve high enantioselectivity.
This document describes a new fluorescent sensor called DDS (dibenzimidazolo diimine sensor) that was designed and synthesized to selectively detect acetate ions. DDS exhibits a remarkable near-infrared emission through an excited state intramolecular proton transfer process. Upon addition of acetate ions, DDS solution changes color visibly from light yellow to pink under normal light. It also shows a large fluorescence enhancement in the near-infrared region, indicating selective detection of acetate ions over other competing anions. Density functional theory calculations help explain the selective binding and sensing mechanism of DDS for acetate ions.
The document discusses how changing the covalent radius of bonds in organic compounds can alter their properties. It presents that increasing the covalent radius will increase the distance between bonded atoms. This increased distance leads to lower melting points, boiling points, and tensile strength. The document constructs virtual models of organic compounds to demonstrate how compounds with the same structure but different covalent radii will have varying distances between atoms and altered properties as a result. It concludes that producing new properties in organic compounds can be achieved by modifying the covalent bond radius.
This document summarizes spectroscopic evidence from electronic absorption, magnetic circular dichroism (MCD), and resonance Raman spectroscopies that provide insight into the unique bonding interaction in oxo-molybdenum dithiolate complexes. The data suggests these complexes have low-energy sulfur to molybdenum charge transfer transitions originating from a set of four filled dithiolate orbitals that are primarily sulfur in character. Resonance Raman excitation profiles allowed assignment of an ene-dithiolate in-plane sulfur to molybdenum transition. Three totally symmetric vibrational modes were also identified. The results provide context for understanding electron transfer pathways in pyranopterin dithiolate centers
New Schiff base ligand (E)-6-(2-(4-
(dimethylamino)benzylideneamino)-2-phenylacetamido)-3,3-
dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic
acid = (HL) Figure(1) was prepared via condensation of
Ampicillin and 4(dimethylamino)benzaldehyde in methanol
.Polydentate mixed ligand complexes were obtained from 1:1:2
molar ratio reactions with metal ions and HL, 2NA on reaction
with MCl2 .nH2O salt yields complexes corresponding to the
formulas [M(L)(NA)2Cl] ,where M =
Fe(II),Co(II),Ni(II),Cu(II),and Zn(II) and NA=nicotinamide.
The 1H-NMR, FT-IR, UV-Vis and elemental analysis
were used for the characterization of the ligand. The complexes
were structurally studied through AAS, FT-IR, UV-Vis,
chloride contents, conductance, and magnetic susceptibility
measurements. All complexes are non-electrolytes in DMSO
solution. Octahedral geometries have been suggested for each
of the complexes. The Schiff base ligands function as
tridentates and the deprotonated enolic form is preferred for
coordination. In order to evaluate the effect of the bactericidal
activity, these synthesized complexes, in comparison to the un
complexed Schiff base has been screened against bacterial
species, Staphy
Schiff base is a compound formed by the condensation reaction of a carbonyl group with a primary amine. The document discusses various methods for preparing Schiff base ligands and complexes, and techniques for characterizing them including UV-visible spectroscopy, IR spectroscopy, NMR, EPR, mass spectrometry, TGA/DTA, and elemental analysis. Schiff base ligands and their complexes have applications in areas like biology, catalysis, materials science, and more.
The Diels-Alder reaction is a [4+2] cycloaddition between a conjugated diene and a substituted alkene (dienophile) to form a cyclohexene ring. It was discovered in 1928 by Otto Diels and Kurt Alder. The reaction proceeds in a single, concerted step through a transition state and can be accelerated by heating or using catalysts. It is useful for synthesizing 6-membered rings in a stereoselective and stereospecific manner. Lewis acids are commonly used to catalyze the reaction by activating the dienophile. Chiral dienes and dienophiles, as well as chiral Lewis acids, allow for asymmetric Diels-A
1) Photolysis of r-azoxy ketones 4a and 4b generates r-azoxy radicals 5a and 5b via R-cleavage. These radicals then undergo rearrangement reactions to form r-benzoyloxyazo compounds 8a and 8b.
2) The ESR spectrum of 5a was analyzed, showing it has an exceptionally large resonance stabilization energy.
3) Azoxy compounds were found to quench triplet excited acetophenone, with the main reaction of model azoxyalkane 7Z in benzene being deoxygenation under irradiation.
The document summarizes the synthesis and characterization of a binuclear Schiff base ligand and its metal complexes with Cu(II), Ni(II), and VO(IV). The ligand was synthesized by reacting 5-bromo-3-fluorosalicylaldehyde and benzidine. The complexes were prepared by reacting the ligand with metal salts. The ligand and complexes were characterized using elemental analysis, IR, NMR, UV-Vis, magnetic susceptibility, and thermal analysis. The ligand behaves as a tetradentate ligand, coordinating through the azomethine nitrogen and deprotonated phenolic oxygen atoms. The complexes exhibit square planar and square pyramidal geometries. Antimicrobial tests found the compounds
The document describes the synthesis of Schiff base ligands derived from citral and valine and their complexes with Cu(II), Ni(II), and Co(II). The structures of the complexes were characterized using IR, UV-vis, and magnetic susceptibility measurements. The Cu(II) and Ni(II) complexes were proposed to have distorted octahedral geometry while the Co(II) complex had square-based pyramidal geometry. Antimicrobial testing showed that the metal complexes had higher activity than the free ligand, with the Co(II) complex being most active.
The peer-reviewed International Journal of Engineering Inventions (IJEI) is started with a mission to encourage contribution to research in Science and Technology. Encourage and motivate researchers in challenging areas of Sciences and Technology.
The [2,3]-Wittig rearrangement is a special class of [2,3]-sigma tropic rearrangement which involves an α-oxy carbanions as the migrating terminus to afford various types of homoallylic alcohols.
Nitrenes slideshare Reactive intermediatesDivyarani K
The document discusses nitrenes, which are electron deficient nitrogen species that can exist in singlet or triplet states. It describes various methods for generating nitrenes, such as through the decomposition of azides or oxidation of primary amino groups. The document also outlines several reactions of nitrenes, including their ability to insert into carbon-hydrogen bonds or undergo rearrangement reactions like the Hofmann, Curtius, Lossen, and Schmidt rearrangements.
The document is the chemistry data booklet for the International Baccalaureate Diploma Programme. It contains relevant equations, physical constants, the electromagnetic spectrum, names and properties of elements, organic compound data, and structural formulas of important chemicals to be provided to chemistry students as a reference for exams.
This presentation has been moved. To view this presentation, please visit http://pubs.acs.org/iapps/liveslides/pages/index.htm?mscNo=jz300725d
Vibrational Circular Dichroism Shows Reversible Helical Handedness Switching in Peptidomimetic lValine Fibrils
Magnesium ion enhances the lanthanum-promoted monobenzoylation of monosaccharides in water. The document describes research into developing a biomimetic reagent for selective acylation in water by mimicking enzymatic aminoacylation of tRNA. Adding magnesium enhances the reaction by complexing with the phosphate byproduct, allowing for catalytic lanthanum and preventing premature reaction stoppage. The synergistic approach of magnesium and lanthanum increases selectivity and establishes a catalytic role for lanthanum in monobenzoylation of carbohydrates in water.
Carbenes- octet defying molecules, its fate, reactions, synthesis of carbenoids,spin multiplicity of carbenes triplet, singlet carbenes, Fischer and Schrock carbenes
This document summarizes a conference presentation on conducting polymer nanofibers and graphene. It discusses how polyacetylene nanofibers have intrinsic conductivity similar to metals. It also summarizes the 2010 Nobel Prize in Physics that was awarded for the discovery of graphene, a single layer of carbon atoms with unusual electronic properties. The document concludes by describing several methods for producing graphene sheets, including mechanical exfoliation of graphite and chemical vapor deposition.
The document provides information about the chemistry syllabus for 12th grade exams. It is divided into two sections, with Section I covering 7 units and Section II covering another 8 units. Each unit lists the maximum marks allotted, both for standard questions and for options. The document also outlines the paper format, with different types of questions and their marks. It provides examples of 1, 2, and 3 mark questions. Finally, it gives short summaries on specific topics from the syllabus, including d-block elements, coordination compounds, and biomolecules.
The homolytic cleavage of covalent bonds in carbonyl compound under photochemical conditions known as Norrish Type Reactions
They are divided into two types
Norrish Type I
Norrish Type II reaction
This document provides an overview of various carbon-based reaction intermediates including carbocations, carbanions, carbenes, free radicals, nitrenes, and nitrenium ions. It discusses their generation, structure, stability, reactions, and detection methods. Key points include that carbocations are positively charged carbon species that react as electrophiles, while carbanions are negatively charged carbon species that react as nucleophiles. Carbenes contain a carbon with six valence electrons in a triplet or singlet state. Free radicals contain one or more unpaired electrons. Nitrenes and nitrenium ions involve a reactive nitrogen species. Detection methods include NMR, EPR, UV-Vis spectroscopy, and trapping reactions.
Polymorphism of Acylglycerols: A Stereochemical Perspectiverjcraven
The underlying cause for polymorphism in acyglycerols has puzzled researchers for more than 150 years. For the last 50 years or so, the subcell concept has been used to describe and understand this phenomenon. In general, there is a correlation between the crystal structure of the various polymorphs and the packing of the polymethylene chains (reflected in the subcell). This occurs because, for acylglcyerols, higher-melting polymorphs form due to an increase in packing efficiency for the polymethylene chains (i.e. packing efficiency increases α < β′ < β) . These same concepts are used to understand polymorphism in waxes and alkanes, and when applied to acylglycerols, they work reasonably well (i.e. as a rule of thumb). They are, however, of limited use in understanding more complex or exceptional polymorphic behaviors. In fact, progress in answering more difficult research problems is hindered, rather than helped, by the current reliance on the subcell concept.
In this work we provide a more fundamental understanding for polymorphism in acylglycerols. Using a stereochemical approach, we are able to provide solutions and mechanisms for research questions that have challenged (and remained unanswered) by many previous workers.
This document summarizes a study that synthesized and characterized the organic compound 1-(pyrazin-2-yl) piperidin-2-ol (PPOL) using computational and experimental methods. Density functional theory calculations were performed to determine the optimized geometry, vibrational frequencies, and electronic properties of PPOL. Experimental Fourier transform infrared, Raman, nuclear magnetic resonance, and UV–visible spectroscopy data were also collected and compared to the computational results. The calculations provide information on the molecular structure, vibrational modes, thermodynamic properties, and electronic structure of PPOL.
This document discusses theoretical and experimental studies on viologen-containing 1,1'-binaphthyls as potential near-infrared chiroptically switching materials. Theoretical modeling was used to correlate chiroptical properties with molecular geometry, showing maximal properties for a twisting angle of 60° and interchromophoric distance of 3.9 nm. Two chiral molecules containing viologen groups attached to a 1,1'-binaphthyl core through short spacers were synthesized and showed strong circular dichroism bands in the visible and near-infrared regions upon electrochemical reduction, demonstrating their potential as chiroptical switches. The cyclic molecule showed stronger chiroptical properties than the open-ring analogue.
This document discusses a study that used microwave spectroscopy to analyze the pure rotational spectra of the open-shell diatomic molecules lead monoiodide (PbI) and tin monoiodide (SnI) for the first time. Spectra were collected using a chirped pulsed Fourier transform microwave spectrometer over the 7-18.5 GHz region. Transitions from multiple isotopologues and vibrational states of PbI and SnI were assigned and fitted to determine rotational, centrifugal distortion, hyperfine, and quadrupole coupling constants. Analysis of the bond lengths and hyperfine interactions indicates that the bonding in both PbI and SnI is ionic in nature.
The Diels-Alder reaction is a [4+2] cycloaddition between a conjugated diene and a substituted alkene (dienophile) to form a cyclohexene ring. It was discovered in 1928 by Otto Diels and Kurt Alder. The reaction proceeds in a single, concerted step through a transition state and can be accelerated by heating or using catalysts. It is useful for synthesizing 6-membered rings in a stereoselective and stereospecific manner. Lewis acids are commonly used to catalyze the reaction by activating the dienophile. Chiral dienes and dienophiles, as well as chiral Lewis acids, allow for asymmetric Diels-A
1) Photolysis of r-azoxy ketones 4a and 4b generates r-azoxy radicals 5a and 5b via R-cleavage. These radicals then undergo rearrangement reactions to form r-benzoyloxyazo compounds 8a and 8b.
2) The ESR spectrum of 5a was analyzed, showing it has an exceptionally large resonance stabilization energy.
3) Azoxy compounds were found to quench triplet excited acetophenone, with the main reaction of model azoxyalkane 7Z in benzene being deoxygenation under irradiation.
The document summarizes the synthesis and characterization of a binuclear Schiff base ligand and its metal complexes with Cu(II), Ni(II), and VO(IV). The ligand was synthesized by reacting 5-bromo-3-fluorosalicylaldehyde and benzidine. The complexes were prepared by reacting the ligand with metal salts. The ligand and complexes were characterized using elemental analysis, IR, NMR, UV-Vis, magnetic susceptibility, and thermal analysis. The ligand behaves as a tetradentate ligand, coordinating through the azomethine nitrogen and deprotonated phenolic oxygen atoms. The complexes exhibit square planar and square pyramidal geometries. Antimicrobial tests found the compounds
The document describes the synthesis of Schiff base ligands derived from citral and valine and their complexes with Cu(II), Ni(II), and Co(II). The structures of the complexes were characterized using IR, UV-vis, and magnetic susceptibility measurements. The Cu(II) and Ni(II) complexes were proposed to have distorted octahedral geometry while the Co(II) complex had square-based pyramidal geometry. Antimicrobial testing showed that the metal complexes had higher activity than the free ligand, with the Co(II) complex being most active.
The peer-reviewed International Journal of Engineering Inventions (IJEI) is started with a mission to encourage contribution to research in Science and Technology. Encourage and motivate researchers in challenging areas of Sciences and Technology.
The [2,3]-Wittig rearrangement is a special class of [2,3]-sigma tropic rearrangement which involves an α-oxy carbanions as the migrating terminus to afford various types of homoallylic alcohols.
Nitrenes slideshare Reactive intermediatesDivyarani K
The document discusses nitrenes, which are electron deficient nitrogen species that can exist in singlet or triplet states. It describes various methods for generating nitrenes, such as through the decomposition of azides or oxidation of primary amino groups. The document also outlines several reactions of nitrenes, including their ability to insert into carbon-hydrogen bonds or undergo rearrangement reactions like the Hofmann, Curtius, Lossen, and Schmidt rearrangements.
The document is the chemistry data booklet for the International Baccalaureate Diploma Programme. It contains relevant equations, physical constants, the electromagnetic spectrum, names and properties of elements, organic compound data, and structural formulas of important chemicals to be provided to chemistry students as a reference for exams.
This presentation has been moved. To view this presentation, please visit http://pubs.acs.org/iapps/liveslides/pages/index.htm?mscNo=jz300725d
Vibrational Circular Dichroism Shows Reversible Helical Handedness Switching in Peptidomimetic lValine Fibrils
Magnesium ion enhances the lanthanum-promoted monobenzoylation of monosaccharides in water. The document describes research into developing a biomimetic reagent for selective acylation in water by mimicking enzymatic aminoacylation of tRNA. Adding magnesium enhances the reaction by complexing with the phosphate byproduct, allowing for catalytic lanthanum and preventing premature reaction stoppage. The synergistic approach of magnesium and lanthanum increases selectivity and establishes a catalytic role for lanthanum in monobenzoylation of carbohydrates in water.
Carbenes- octet defying molecules, its fate, reactions, synthesis of carbenoids,spin multiplicity of carbenes triplet, singlet carbenes, Fischer and Schrock carbenes
This document summarizes a conference presentation on conducting polymer nanofibers and graphene. It discusses how polyacetylene nanofibers have intrinsic conductivity similar to metals. It also summarizes the 2010 Nobel Prize in Physics that was awarded for the discovery of graphene, a single layer of carbon atoms with unusual electronic properties. The document concludes by describing several methods for producing graphene sheets, including mechanical exfoliation of graphite and chemical vapor deposition.
The document provides information about the chemistry syllabus for 12th grade exams. It is divided into two sections, with Section I covering 7 units and Section II covering another 8 units. Each unit lists the maximum marks allotted, both for standard questions and for options. The document also outlines the paper format, with different types of questions and their marks. It provides examples of 1, 2, and 3 mark questions. Finally, it gives short summaries on specific topics from the syllabus, including d-block elements, coordination compounds, and biomolecules.
The homolytic cleavage of covalent bonds in carbonyl compound under photochemical conditions known as Norrish Type Reactions
They are divided into two types
Norrish Type I
Norrish Type II reaction
This document provides an overview of various carbon-based reaction intermediates including carbocations, carbanions, carbenes, free radicals, nitrenes, and nitrenium ions. It discusses their generation, structure, stability, reactions, and detection methods. Key points include that carbocations are positively charged carbon species that react as electrophiles, while carbanions are negatively charged carbon species that react as nucleophiles. Carbenes contain a carbon with six valence electrons in a triplet or singlet state. Free radicals contain one or more unpaired electrons. Nitrenes and nitrenium ions involve a reactive nitrogen species. Detection methods include NMR, EPR, UV-Vis spectroscopy, and trapping reactions.
Polymorphism of Acylglycerols: A Stereochemical Perspectiverjcraven
The underlying cause for polymorphism in acyglycerols has puzzled researchers for more than 150 years. For the last 50 years or so, the subcell concept has been used to describe and understand this phenomenon. In general, there is a correlation between the crystal structure of the various polymorphs and the packing of the polymethylene chains (reflected in the subcell). This occurs because, for acylglcyerols, higher-melting polymorphs form due to an increase in packing efficiency for the polymethylene chains (i.e. packing efficiency increases α < β′ < β) . These same concepts are used to understand polymorphism in waxes and alkanes, and when applied to acylglycerols, they work reasonably well (i.e. as a rule of thumb). They are, however, of limited use in understanding more complex or exceptional polymorphic behaviors. In fact, progress in answering more difficult research problems is hindered, rather than helped, by the current reliance on the subcell concept.
In this work we provide a more fundamental understanding for polymorphism in acylglycerols. Using a stereochemical approach, we are able to provide solutions and mechanisms for research questions that have challenged (and remained unanswered) by many previous workers.
This document summarizes a study that synthesized and characterized the organic compound 1-(pyrazin-2-yl) piperidin-2-ol (PPOL) using computational and experimental methods. Density functional theory calculations were performed to determine the optimized geometry, vibrational frequencies, and electronic properties of PPOL. Experimental Fourier transform infrared, Raman, nuclear magnetic resonance, and UV–visible spectroscopy data were also collected and compared to the computational results. The calculations provide information on the molecular structure, vibrational modes, thermodynamic properties, and electronic structure of PPOL.
This document discusses theoretical and experimental studies on viologen-containing 1,1'-binaphthyls as potential near-infrared chiroptically switching materials. Theoretical modeling was used to correlate chiroptical properties with molecular geometry, showing maximal properties for a twisting angle of 60° and interchromophoric distance of 3.9 nm. Two chiral molecules containing viologen groups attached to a 1,1'-binaphthyl core through short spacers were synthesized and showed strong circular dichroism bands in the visible and near-infrared regions upon electrochemical reduction, demonstrating their potential as chiroptical switches. The cyclic molecule showed stronger chiroptical properties than the open-ring analogue.
This document discusses a study that used microwave spectroscopy to analyze the pure rotational spectra of the open-shell diatomic molecules lead monoiodide (PbI) and tin monoiodide (SnI) for the first time. Spectra were collected using a chirped pulsed Fourier transform microwave spectrometer over the 7-18.5 GHz region. Transitions from multiple isotopologues and vibrational states of PbI and SnI were assigned and fitted to determine rotational, centrifugal distortion, hyperfine, and quadrupole coupling constants. Analysis of the bond lengths and hyperfine interactions indicates that the bonding in both PbI and SnI is ionic in nature.
Determination of nonlinear absorption (β) and refraction (n2)by the Z-scan me...IOSR Journals
Potassium Pentaborate nonlinear optical (NLO) material was synthesized by the solution growth method. The grown crystals were subjected to structural, optical and mechanical property studies. Crystal with excellent transparency were grown with maximum size of 9mm×8mm×5mm and the grown crystals were characterized by single crystal Single crystal XRD, FT-IR, TGA-DTA&DSC, and UV–vis-NIR studies. The crystal belongs to orthorhombic with a space group of mm2 having unit-cell dimensions a = 11.068Åb= 11.175Å c = 9.058Åand α = 90°; β = 90°; and γ =90°; Z=4, at 298(2) K. The second-order nonlinear optical property of the polycrystalline sample has been confirmed by Kurtz-Perry powder SHG analysis. Third order nonlinear optical properties were also studied by Z-scan techniques. Nonlinear absorption and nonlinear refractive index were found out and the third order bulk susceptibility of compound was also calculated.
This document discusses near-infrared spectroscopy and its applications in food analysis. It begins with an introduction to near-infrared spectroscopy, including the physics behind molecular vibrations and overtones that produce absorption bands in the near-infrared region. It then covers instrumentation used in near-infrared spectroscopy, different methods for sample presentation including diffuse transmittance and reflectance, and considerations for calibration development and qualitative analysis. The document concludes by reviewing various food applications and limitations of near-infrared spectroscopy in food analysis.
This document discusses the optical properties of nanostructured metals. Plasmons, which are the collective oscillations of conduction electrons, lead to resonance phenomena in these structures. Plasmon modes exist in different geometries and metals, and can be excited by light, causing strong light scattering, absorption, and enhancement of the local electromagnetic field. In the late 1980s, it was proposed that a composite particle with a dielectric core and metallic shell could produce plasmon resonance modes across a wider range of wavelengths. In the 1990s, the first gold nanoshells were created with an Au2S core and gold shell, though they were limited in size. Improved synthesis allowed for silica-core gold nanoshells over 40
Vapour Sensing Properties of Bio-Inspired Synthetic NanostructuresLaurent Francis
This document discusses bio-inspired synthetic nanostructures for vapour sensing applications. It describes how the structures were inspired by photonic architectures found in Morpho butterfly scales and Papilio blumei wings. The nanostructures showed highly selective responses to different vapours and an increased colour response with changes in ambient refractive index, similar to the natural structures. The document suggests these bio-inspired designs could enable applications like anti-counterfeiting or infrared photon detection.
This document summarizes a study on the synthesis and NMR analysis of various Naproxen and Ibuprofen ester derivatives. Several diastereoisomeric Naproxyl-Naproxenate, Naproxyl-Ibuprofenate, and Ibuprofyl-Naproxenate esters were synthesized. Variable temperature NMR experiments showed differences in aromatic ring dynamics between esters, likely due to varying axial rotation speeds. Chiral shift reagent NMR experiments were also performed and provided insights into epimerization levels, assignments of proton signals, and geometries of the ester complexes.
Synthesis, Spectroscopic study & Biological Activity Of Some Organotin(Iv) De...IOSR Journals
Some di-and triorganotin(IV) derivatives of (2E)-N-methyl-(2
oxo1,2diphenylethylidne)hydrazinecarbothioamide synthesised by the reactions of the corresponding di and
triorganotin(IV) chlorides with the sodium salt of (2E)-N-methyl-(2-
oxo1,2diphenylethylidne)hydrazinecarbothioamide in different molar ratios. These derivatives have been
characterized by elemental analyses ,molecular weights, conductivity measurements and spectral(IR, 1H, 13C
and 119 Sn NMR) studies.
This document describes research into the inner-sphere and outer-sphere reduction of uranyl supported by a redox-active dipyrrin ligand. A new uranyl(VI) chloride complex (2) was synthesized and its structure determined. Complex 2 undergoes either inner-sphere reduction by [TiCp2Cl]2, forming a U(IV) complex (3), or outer-sphere reduction by CoCp2, initially reducing the ligand before further reducing U(VI) to U(V). The involvement of the redox-active ligand allows access to U(VI), U(V) and U(IV) complexes through these reduction pathways.
The document reports on a study of mutations to the arginine residue at position 257 (R257) of the D1 protein in Photosystem II in Chlamydomonas reinhardtii. Three mutations were made - R257E, R257K, and R257Q. Thermoluminescence measurements and fluorescence analysis showed that the redox potential of the QB/QB- pair was lowered by 20-40 mV in the mutants. This suggests the size and charge of the residue at position 257 modulates the redox potential of QB/QB-. The mutants also showed decreased growth rates and lowered maximum variable chlorophyll fluorescence compared to wild type.
34th Annual Mid-West Photosynthesis Conference at Turkey Run State Park, INSean Padden
The document reports on a study of mutations to the arginine residue at position 257 (R257) of the D1 protein in Photosystem II in Chlamydomonas reinhardtii. Three mutations were made - R257E, R257K, and R257Q. Thermoluminescence and fluorescence measurements showed that the redox potential of the QB/QB- pair was lowered by 20-40 mV in the mutants. This suggests the size and charge of the residue at position 257 modulates the redox potential of QB/QB-. Growth rates and oxygen evolution were negatively impacted in the mutants compared to wild type.
Electrochemical, in-vitro in-vivo study of Co (II)-ofloxacin complexIOSR Journals
Ofloxacin complex has been synthesized and screened for its physicochemical, microbial as well as pharmacological activity have been done in solid and aqueous phase. On the basis of elemental analysis, polarographic studies, amperometric titration and IR spectral studies the probable formula for the complex has been determined at 30±1OC and ionic strength of μ= 1.0[KCl]. Raper’s paper disc method was used for microbial study against various pathogenic bacteria and fungi.Invivo syudy of Swiss mice [25-30gm] were used for antibacterial activity against ofloxacin and its complex on xyline-Alcoholic activity test Kidney, liver and serum of these rats were also studied. On the basis of observed result it could be concluded that Co(II)-Ofloxacin complex were found to be non-toxic and more potent than pure Ofloxacin.(1)
This study systematically analyzed the effect of local ordering of B-cations (Zr and Ti) on the electronic, optical, and piezoelectric properties of PbZrxTi1-xO3 (PZT) using density functional theory calculations. The most stable structure found was a tetragonal phase with P4mm symmetry. Other stable phases included a polar orthorhombic phase and a non-polar triclinic phase. Analysis showed that different arrangements of B-cations led to variations in the electronic structure, polarization, and piezoelectric response of the materials. In particular, large piezoelectric coefficients e15 and e33 were associated with specific planar and axial arrangements of
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
1. Conjugated systems with multiple double bonds have increased stability due to delocalization of pi electrons over the entire system. This stabilization increases reactivity for electrophilic additions.
2. Allylic positions adjacent to double bonds have increased reactivity due to stabilization of allylic radicals, cations and transition states by resonance with the pi system. This leads to faster halogenation, SN1 and SN2 reactions at allylic sites.
3. Extended conjugation over multiple double bonds confers increased thermodynamic stability but also increased reactivity towards electrophilic additions and radical reactions compared to shorter conjugated systems.
Experimental (FT-IR, UV-visible, NMR) spectroscopy and molecular structure, g...iosrjce
IOSR Journal of Biotechnology and Biochemistry (IOSR-JBB) covers studies of the chemical processes in living organisms, structure and function of cellular components such as proteins, carbohydrates, lipids, nucleic acids and other biomolecules, chemical properties of important biological molecules, like proteins, in particular the chemistry of enzyme-catalyzed reactions, genetic code (DNA, RNA), protein synthesis, cell membrane transport, and signal transduction. IOSR-JBB is privileged to focus on a wide range of biotechnology as well as high quality articles on genetic engineering, cell and tissue culture technologies, genetics, microbiology, molecular biology, biochemistry, embryology, cell biology, chemical engineering, bioprocess engineering, information technology, biorobotics.
The document discusses Muhammad Aadil's PhD research presentation on UV-Visible spectroscopy. It introduces spectroscopy, the electromagnetic spectrum, and the principle of UV-Visible spectroscopy involving electronic transitions. It describes the instrumentation including light sources, monochromators, sample holders, and detectors. It discusses Beer-Lambert's law and its use in quantitative analysis. Key terms like chromophores and auxochromes are defined. Applications to analyze the reduction of graphene oxide and formation of metal nanoparticles are mentioned. Common questions about the technique are also listed.
This document presents a theoretical study examining the effects of central metal ions (Cd2+, Hg2+, Pt2+) and substituent groups (F, I, NO2, NH2, CH3, H) on the properties of metalloporphyrin complexes for use as semiconductor materials. Density functional theory calculations were used to analyze the electronic structure, density of states, and UV-Vis absorption spectra of the complexes. The results showed that electron-donating substituents and central ions from Hg to Cd to Pt decreased the bandgap and shifted absorption peaks to longer wavelengths, indicating better semiconductor performance for light absorption. NH2 substituents gave the best results with the smallest bandgap and longest absorption peak.
Similar to Organic Letters 2007,9(26),5393 5396 (20)
The document discusses drugs for type 2 diabetes that are inhibitors of DPP-4, including sitagliptin, vildagliptin, saxagliptin, alogliptin, and linagliptin. It lists the generic and brand names of the drugs, along with their companies and FDA approval dates in the United States and European Union.
Jian Deng is a synthetic chemist with experience in organic synthesis, polymer chemistry, and computational modeling. He has a PhD in polymer chemistry from Peking University and worked as a postdoc at the University of Wisconsin-Milwaukee. He is proficient in organic synthesis techniques and characterization methods. His research focuses on designing and synthesizing chiral small molecules and functional polymers for applications such as organic electronics and solar cells.
The document summarizes the synthesis of several compounds. Key reactions include:
1) Synthesis of (R)-BE from (R)-BINOL involving esterification.
2) Synthesis of (R)-BEBP and (R)-CBEBPB involving substitution, bromination and addition of PF6 groups.
3) Synthesis of PPB and (R)-BBEBPP involving substitution and addition of PF6 groups.
4) Synthesis of monomer (R)-DBB involving bromination and esterification.
5) Polymerization of (R)-DBB to form P1, P2 and P3 polymers.
This document describes a new method for producing stable carbon nanotube (CNT) aerogels with high electrical conductivity and porosity. The method involves:
1) Forming a chemically cross-linked gel of CNTs in solution using a chemical cross-linker.
2) Drying the gel using supercritical CO2 to produce an aerogel without shrinkage.
3) Thermally annealing the aerogel in air, which improves electrical conductivity, mechanical stability, surface area, and porosity by reopening pores.
The resulting annealed CNT aerogels are highly porous (>99%), electrically conductive (1-2 S/cm), and have a large specific surface area (590
This document describes the synthesis and characterization of a new type of optically active polymer. The polymer was created by grafting electrochromic viologen groups to the side chains of a helical polyacetylene backbone. This produced a polymer with a single-handed helical structure and viologens positioned asymmetrically along the chains. The polymer exhibited large optical rotation and new circular dichroism bands in the visible/near-infrared range upon reduction of the viologens. It also demonstrated redox-switchable chiroptical properties, making it a potential material for applications like chirowaveguides.
This document summarizes research on the photophysical behavior of fluorescein bonded to polyamidoamine dendrimers based on silica nanoparticles of different generations. Excimer fluorescent emission was observed for the lowest generation (G0F) dendrimer, while fluorescein-fluorescein complex fluorescent emissions were observed for the first (G1F) and second (G2F) generation dendrimers. The different photophysical behaviors in various suspensions indicated that hydrogen bonding interactions play a crucial role in forming either excimers or fluorescein-fluorescein complexes. These results could help in the design and development of fluorescent sensors using this core-shell nanosilica system.
This document discusses simulating UV-vis spectra of methyl viologen and its radical cation using time-dependent density functional theory (TD-DFT). It optimizes the geometries of methyl viologen and its radical cation using DFT and discusses using TD-DFT with a 6-311G** basis set to simulate the UV-vis spectra. It also plans to simulate the UV-vis spectra using a multi-reference method called CASPT2.
The document summarizes research on designing and synthesizing near-infrared chiroptically switching materials. It establishes a structural model correlating geometry with the magnitude of chiroptical properties. This aids the design of two novel molecular switches that exhibit very large near-infrared chiroptical switching properties for the first time. A novel optically active polymer with electrochromic viologens on side chains and a minor-groove cisoid main chain was also prepared, showing pronounced redox-based spectral changes and good chiroptical switching properties.
This document discusses qualitative analysis of circular dichroism spectra using exciton theory. It outlines the concepts of energy splitting, dipole moments, and exciton coupling theory. It then applies these concepts to analyze the circular dichroism spectra of specific chiral molecules, (R)-BEBPB and (R)-CBEBPB, through geometric optimization calculations and determining the origin of observed peaks. The conclusions find that specific peaks are mainly due to dipole interactions between different chromophores in the molecules.
Construction Of Near Infrared Chiroptical Switches Based On Electrochromic Vi...niba50
The document discusses the development of near-infrared chiroptical polymers based on electrochromic viologens. It outlines the background, hypothesis, experimental approach, and results. Key compounds were synthesized and showed electrically switchable circular dichroism in the near-infrared region. Future work includes optimizing properties through structural modifications and theoretical calculations to better understand structure-property relationships.
2. the readiness in operation and the well-documented photo- obtained as light-yellow powders. No melting point was
isomerizable systems such as azobenzenes, diarylethenes, spi- detected for them below 250 °C. The chemical structures of
ropyrenes, fulgides, and overcrowded alkenes.1,5 In contrast, (R)-1 and (R)-2 were confirmed by 1H NMR, 13C NMR, and
electrically driven chiroptical switches based on the electro- mass spectroscopy (see Supporting Information).
chromism of chiral systems are relatively less known,4 Figure 1 shows the UV-vis absorption spectra of (R)-
although the drastic changes in absorption for electrochromic BEB, (R)-1, and (R)-2 in acetonitrile. For comparison, the
systems6 may be utilized to achieve efficient chiroptical
switches.
Herein, we present a novel type of electrically driven,
chiroptical switching molecules (R)-1 and (R)-2 based on
the axially dissymmetric 1,1′-binaphthyl and the electro-
chromic 4,4′-bipyridinium (or viologen). Such chiral mol-
ecules are designed to take advantage of the strong chiral
force of 1,1′-binaphthyl-2,2′-diyls7 and the well-studied
electrochromic behavior of viologens.6,8,9 (R)-1 and (R)-2
differ from each other in terms of the open-ring and the cyclic
configuration. Given that chiroptical properties depend on
both absorption properties and dissymmetric spatial arrange-
ment (e.g., distance and orientation) of interacting chro-
mophores,10,11 different chiroptical switching properties are
expected for (R)-1 and (R)-2.
The synthesis of (R)-1 and (R)-2 was accomplished by
reacting benzyl bromide and 1,3-dibromomethyl benzene,
respectively, with (R)-BEBP that was in turn prepared by
the reaction between (R)-2,2′-dibromoethyloxy-1,1′-binaph- Figure 1. UV-vis absorption spectra of (R)-1, (R)-2, (R)-BEB,
thyl [(R)-BEB]12 and 4,4′-bipyridine (Scheme 1, see Sup- and BPP in acetonitrile. The solution concentrations were in the
range of 1-3 × 10-4 M. The intensities were adjusted for a better
comparison. (Inset) UV-vis absorption spectra of (R)-1 and (R)-2
in DMF after electrochemical reduction to the violene states.
Scheme 1. Synthesis of Chiral Molecules (R)-1 and (R)-2
absorption spectrum of 1,1′-dipropyl-4,4′-bipyridinium salt
of hexafluorophosphate (BPP) in acetonitrile is also dis-
played. From the figure it can be clearly seen that the UV-
vis absorptions of (R)-1 and (R)-2 are mainly composed of
the absorptions of constituting components, i.e., (R)-BEB at
229 nm and BPP at 267 nm. A weak absorption at 400 nm
was observed for BPP, (R)-1, and (R)-2 and may be attributed
to the presence of a slight amount of radical cations (or
violenes, the semireduced state of viologen) resulting from
the photoinduced electron transfer of samples during the
UV-vis measurements or sample storage. A diffused
absorption band in the range of 360-530 nm was discernible
for (R)-1 and (R)-2 but absent in the spectra of (R)-BEB
and BPP. An intramolecular charge transfer from the
binaphthyl to the viologens may account for such an
absorption behavior.13
porting Information). The counter anions of (R)-1 and (R)-2 (7) Pu, L. Chem. ReV. 1998, 98, 2405.
(8) Anelli, P. L.; Ashton, P. R.; Ballardini, R.; Balzani, V.; Delgado,
were exchanged from bromide to hexafluorophosphate to M.; Gandolfi, M. T.; Goodnow, T. T.; Kaifer, A. E.; Philp, D.; Pietraszk-
achieve a good organosolubility such as in acetonitrile and iewicz, M.; Prodi, L.; Reddington, M. V.; Slawin, A. M. Z.; Spencer, N.;
Stoddart, J. F.; Vicent, C.; Williams, D. J. J. Am. Chem. Soc. 1992, 114,
N,N′-dimethylformamide (DMF). Both (R)-1 and (R)-2 were 193.
(9) Geuder, V.; Hunig, S.; Suchy, A. Tetrahedron 1986, 42, 1665.
(5) (a) Irie, M. Chem. ReV. 2000, 100, 1685. (b) Yokoyama, Y. Chem. (10) (a) Elliot, C., Ed. The Molecular Basis of Optical ActiVity: Optical
ReV. 2000, 100, 1717. (c) Berkovic, G.; Krongauz, V.; Weiss, V. Chem. Rotatory Dispersion and Circular Dichroism; John Wiley: New York, 1979.
ReV. 2000, 100, 1741. (b) Harada, N., Nakanishi, K., Eds. Circular Dichroic Spectroscopy-Exciton
(6) (a) Mortimer, R. J. Chem. Soc. ReV. 1997, 26, 147. (b) Mortimer, R. Coupling in Organic Stereochemistry; University Science Books: Mill
J. Electrochim. Acta 1999, 44, 2971. (c) Wang, Z. Y.; Zhang, J.; Wu, X.; Valley, CA, 1983.
Birau, M.; Yu, G.; Yu, H.; Qi, Y.; Desjardins, P.; Meng, X.; Gao, J. P.; (11) Eyring, H.; Liu, H.-C.; Caldwell, D. Chem. ReV. 1968, 68, 525.
Todd, E.; Song, N.; Bai, Y.; Beaudin, A. M. R.; LeClair, G. Pure Appl. (12) Prepared according to the reference method: Stock, T. H.; Kellogg,
Chem. 2004, 76, 1435. R. M. J. Org. Chem. 1996, 61, 3093.
5394 Org. Lett., Vol. 9, No. 26, 2007
3. The redox properties of (R)-1 and (R)-2 were investigated as zinc powders or tin particles. Since chiroptical properties
in DMF solution by cyclic voltammetry. Since both (R)-1 of a chiral molecule (e.g., optical rotation dispersion and
and (R)-2 contain two viologen units and each viologen units circular dichroism) depend greatly on the absorption proper-
can undergo a two-step reduction, a total of four steps in ties,10,11 such a drastic change in absorption is expected to
reduction, each involving a one-electron process, may be lead to a significant change in chiroptical properties once
expected. Figure 2 shows the cyclic voltammograms of (R)-1 the viologens are placed dissymetrically in proximity, such
as in the case of (R)-1 and (R)-2. Hunig et al.9 studied in
¨
detail the pimerization of violenes in different systems and
ascribed pimerized violenes to an absorption at 537 nm. In
our study, no obvious pimerization of violenes in cyclic (R)-2
was observed. In contrast, intermolecular pimerization of
violenes occurred for (R)-1 at a high concentration of radical
cations, as evidenced by a blue shift of the maximum
absorption from 610 to 548 nm that took place for the low-
energy band as the electrochemical reduction of (R)-1 (c )
0.28 mM) lengthened to over 3 min (see Supporting
Information).
The chiroptical properties of (R)-1 and (R)-2 were
examined using a polarimeter and a CD spectrometer. (R)-1
has an optical rotation of [R]D ) -39.5° (0.4, MeCN),
whereas (R)-2 has an opposite sign of the optical rotation of
[R]D ) +55.0° (0.4, MeCN). An effort to measure the optical
rotation of the violenes of (R)-1 and (R)-2 failed due to the
strong absorption at the measurement wavelengths (i.e., 365-
Figure 2. Cyclic voltammograms of (R)-1 and (R)-2 measured in 598 nm). As shown in the CD spectrum (Figure 3), (R)-1
0.1 M Bu4NClO4/DMF. Working electrode: glassy carbon; counter
electrode: Pt wire; reference electrode: AgCl/Ag.
and (R)-2. Only two redox processes at E1/2 ) -0.40 and
-0.85 V were found for the open-ring tetracation (R)-1,
comparable to the redox pattern of BPP, suggesting that the
two viologens behave individually and do not interact with
each other to a great extent. In contrast, the cyclic tetracation
(R)-2 exhibited three redox processes at E1/2 ) -0.37, -0.74,
and -0.86 V, with the first reduction that corresponds to
the reduction to the double radical cation state occurring more
easily by 30 mV than that for (R)-1. The second and the
third reductions, corresponding to the reductions to the radical
cation-neutral and neutral-neutral state, respectively, differ
from each other by about 120 mV. Given the similar
chemical constitutions of (R)-1 and (R)-2, such a different
redox pattern can be attributed to the intramolecular interac-
tions between the two viologens in (R)-2, which contribute
Figure 3. CD spectra of (R)-1 and (R)-2 in acetonitrile. (Inset)
to the stabilization of radical cations and the radical cation- Enlarged CD spectrum of (R)-1.
neutral state. Hunig et al.9 and Stoddart et al.8 observed
¨
similar redox patterns for their cyclophanes containing two
viologen units. exhibited a strong exciton couplet centered at 227 nm ([θ]
The electrochromic properties of (R)-1 and (R)-2 were ) 5.0 × 105 deg‚cm2/dmol), corresponding to the binaphthyl
examined by UV-vis spectroscopy in DMF solutions (Figure unit, and a relatively weak exciton couplet at 268 nm ([θ]
1, inset). Upon electrochemical reduction to the radical ) 4.2 × 104 deg‚cm2/dmol, inset of Figure 3), corresponding
cations, drastic changes in absorption took place with the to the absorption of viologens. (R)-2 exhibited a similar
appearance of two strong absorption bands at around 402 ( pattern of the CD spectrum, but with very different intensi-
) 41800) and 610 nm ( ) 13900).14 The same change in ties. The CD intensities of (R)-2 at the binaphthyl and the
absorption can also be readily achieved by bubbling nitrogen viologen absorption regions are about 12 and 20 times,
slowly into the solution or by adding reducing agents such respectively, higher than those for (R)-1. From the Kirk-
wood’s coupled oscillator model,11 it is known that the
(13) Park, J. W.; Lee, B. A.; Lee, S. Y. J. Phys. Chem. B 1998, 102,
8209. intensity of CD signals depends greatly on the dissymmetric
(14) Watanabe, T.; Honda, K. J. Phys. Chem. 1982, 86, 2617. spatial arrangement of interacting chromophores, in particular
Org. Lett., Vol. 9, No. 26, 2007 5395
4. on the distance and the relative twisting angles between
chromophores. Thus, the differences in the CD spectrum
between (R)-1 and (R)-2 could be attributed to a more
appropriate positioning of viologen moieties in (R)-2 due to
the rigid cyclic structure.
Upon electrochemical reduction of (R)-1 and (R)-2 at a
potential of -0.5 V to the violenes, two new CD bands
appeared at the positions similar to the absorption bands at
400 and 600 nm, respectively (Figure 4). As the reduction
Figure 5. Demonstration of electrochemical switching of CD
signals of (R)-2 in 0.1 M Bu4NClO4/DMF. (a) First reduction at
-0.5 V for 5 s; (b) tetracation recovered by shaking the cell in the
air; (c) second reduction at -0.7 V for 1 min.
tion of the negative voltage (-0.7 V, 1 min) to the cell
regenerated the blue color as well as the CD signals at the
low-energy bands. These results indicate that it is pos-
sible to modulate the chiroptical properties of the resulting
new chiral systems by applying a bias voltage and monitoring
the CD signals in the visible region, e.g., at 400 and 660
nm.
In summary, novel types of chiroptical switching mol-
ecules based on axially dissymmetric 1,1′-binaphthyl and
electrochromic viologens were prepared and characterized.
Figure 4. CD and UV-vis absorption spectra of radical cations
of (R)-1 and (R)-2 obtained by electrochemical reduction in 0.1 M These compounds exhibited reversible, drastic changes in
Bu4NClO4/DMF. The concentrations of sample solutions were their absorption and CD spectra when electrochemically
around 2.8 mM. Working electrode: Pt grid; counter electrode: reduced to the violene state. The readiness in reading out
Pt wire (0.5 mm diameter); reference electrode: AgCl/Ag. the chiroptical changes between the two redox states in the
visible region (e.g., from [θ] ≈ 0 deg‚cm2/dmol for the
tetracation state to [θ] ≈ -1.6 × 105 deg‚cm2/dmol15 for
time extended, the intensity of these CD signals increased the double radical cation state at 660 nm) demonstrates a
due to the increase of violene concentration. In comparison high potential for electrically driven chiroptical switches.
between (R)-1 and (R)-2, the latter exhibited much stronger
CD signals than the former at the same reduction time, Acknowledgment. We thank the National Natural Sci-
presumably due to a more favorable dissymmetric arrange- ence Foundation of China (Grant No. 20774002) and the
ment of violenes. Considering that the magnitude of signal SRF for ROCS, SEM for financial support.
change is one of the important factors for switching applica- Supporting Information Available: Synthetic procedures
tions, the cyclic tetracation (R)-2 appears to be superior than and characterization data for (R)-1 and (R)-2; time depen-
the open-ring (R)-1 for use as chiroptical switches. dence of UV-vis spectroelectrochemistry of (R)-1. This
The electrically driven chiroptical switching property of material is available free of charge via the Internet at
(R)-2 was demonstrated in DMF solution. As shown in http://pubs.acs.org.
Figure 5, the reduction of (R)-2 to the violene by applying
OL701822U
a voltage of -0.5 V for 5 s led to a deep blue color
accompanied by the appearance of two new CD bands at (15) Molar ellipticity caculated for (R)-2 that was reduced in 0.1 M Bu4-
around 400 and 660 nm. When the resulting blue solution NClO4/DMF solution for 57 s at a potential of -0.5 V. The concentration
of the double radical cation in the solution was estimated from the UV-
was disturbed by shaking in the air, the original light-yellow vis absorptions of the sample at 402 nm and 610 nm and by using the
color recovered, and the CD signals disappeared. Reapplica- extincition coefficients reported in reference 14.
5396 Org. Lett., Vol. 9, No. 26, 2007