Home About us Contact
|
Home About us Contact | ||
|
|
||
Charge-transfer Complexes (charge-transfer + complex)
Selected AbstractsSupramolecular Amphiphiles Based on a Water-Soluble Charge-Transfer Complex: Fabrication of Ultralong Nanofibers with Tunable Straightness,ANGEWANDTE CHEMIE, Issue 47 2009Chao Wang Die Basenstärke entscheidet: Die Bildung eines Charge-Transfer-Komplexes wird durch eine Kombination aus Coulomb-Anziehung und Charge-Transfer-Wechselwirkungen bestimmt. Der Charge-Transfer-Komplex, der aus einem supramolekularen Amphiphil erhalten wurde (siehe Bild), ist wasserlöslich und bildet ultralange Nanofasern, deren Geradheit über den pH-Wert der Lösung eingestellt werden kann. [source] Quantum Dots Arrangement and Energy Transfer Control via Charge-Transfer Complex Achieved on Poly(Phenylene Ethynylene)/Schizophyllan NanowiresCHEMISTRY - AN ASIAN JOURNAL, Issue 9 2009Tomohiro Shiraki Abstract Assemblies of organic and inorganic compounds in the nanoscale region have contributed to the development of novel functional materials toward future applications, including sensors and opto-electronics. We succeed in fabricating hybrid nanowires composed of a conjugated polymer and semiconductor quantum dots (QDs) by a supramolecular assembly technique. The 1-D fashion of the nanowire structure is obtained by the polymer wrapping of cationic poly(phenylene ethynylene) (PPE) with helix-forming polysaccharide schizophyllan (SPG). The electrostatic interaction between cationic PPE and anionic QDs affords the nanowires decorated with QDs. Upon addition of an acceptor molecule, tetranitrofluorenone (TNF), the charge-transfer (CT) complex between PPE and TNF is formed, resulting in energy transfer from the QDs to PPE arising from the induced spectral overlap. Furthermore, the employment of the conjugated polymer allows highly sensitive quenching of the QD's emission by raising the transmission efficiency to the CT complexed electron deficient sites along the polymer backbone. [source] Charge-Transfer Complexes Between the Sulfur Molecules SO2, S2O, S3, SONH, and SOCl2 and the Amine Donors NH3 and NMe3 , A theoretical StudyCHEMINFORM, Issue 47 2007Ralf Steudel Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Organic and polymer chemistry of electrophilic tri- and tetrasubstituted ethylenesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2004H. K. Hall Jr. Abstract A survey of the spontaneous reactions of electrophilic olefins and nucleophilic olefins is presented as an area in which organic chemistry merges with polymer chemistry. The products include both small molecules and polymers, arising via tetramethylene biradical zwitterions that can cyclize or initiate polymerizations. Electrophilic tri- and tetrasubstituted olefins are particularly useful in delineating the transition from radical chemistry to ionic chemistry. A periodic table embodying these results enables predictions. Charge-transfer complexes, although observed in many of these reactions, play no significant role. Various aspects arising from these investigations include new cationic initiators, Lewis acid catalysis, quinodimethane chemistry, and photochemistry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2845,2858, 2004 [source] Nanomorphology and Charge Generation in Bulk Heterojunctions Based on Low-Bandgap Dithiophene Polymers with Different Bridging AtomsADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Mauro Morana Abstract Carbon bridged (C-PCPDTBT) and silicon-bridged (Si-PCPDTBT) dithiophene donor,acceptor copolymers belong to a promising class of low bandgap materials. Their higher field-effect mobility, as high as 10,2,cm2 V,1,s,1 in pristine films, and their more balanced charge transport in blends with fullerenes make silicon-bridged materials better candidates for use in photovoltaic devices. Striking morphological changes are observed in polymer:fullerene bulk heterojunctions upon the substitution of the bridging atom. XRD investigation indicates increased ,,, stacking in Si-PCPDTBT compared to the carbon-bridged analogue. The fluorescence of this polymer and that of its counterpart C-PCPDTBT indicates that the higher photogeneration achieved in Si-PCPDTBT:fullerene films (with either [C60]PCBM or [C70]PCBM) can be correlated to the inactivation of a charge-transfer complex and to a favorable length of the donor,acceptor phase separation. TEM studies of Si-PCPDTBT:fullerene blended films suggest the formation of an interpenetrating network whose phase distribution is comparable to the one achieved in C-PCPDTBT:fullerene using 1,8-octanedithiol as an additive. In order to achieve a balanced hole and electron transport, Si-PCPDTBT requires a lower fullerene content (between 50 to 60,wt%) than C-PCPDTBT (more than 70,wt%). The Si-PCPDTBT:[C70]PCBM OBHJ solar cells deliver power conversion efficiencies of over 5%. [source] UV-vis-Induced Vitrification of a Molecular Crystal,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2007T. Naito Abstract A charge-transfer complex of 2,5-dimethyl- N,N,-dicyanoquinonediimine (DM) with silver (crystalline Ag(DM)2, defined as ,) is irreversibly transformed by UV-vis illumination. Depending on the illumination conditions, three new types of solids (defined as ,, ,, and ,) with different structural and physical properties are obtained and examined by a variety of analytical techniques, including solid-state, high-resolution, cross-polarization magic angle spinning (CP-MAS) 13C,NMR, elemental analysis (EA), mass spectrometry (MS), X-ray absorption fine structure (XAFS), and powder X-ray diffraction (XRD). The CP-MAS, EA, MS, and XAFS results indicate that compound , is a glass state of Ag(DM)2. The transformation from crystalline (,) to amorphous (,) solid Ag(DM)2 is an irreversible exothermic glass transition (glass-transition temperature 155.2,°C; ,H,=,,126.8,kJ,mol,1), which implies that the glass form is thermodynamically more stable than the crystalline form. Compound , (Ag(DM)1.5) consists of silver nanoparticles (diameter (7,±,2),nm ) dispersed in a glassy matrix of neutral DM molecules. The N,CN,Ag coordination bonds of the , form are not maintained in the , form. Decomposition of , by intense illumination results in a white solid (,), identified as being composed of silver nanoparticles (diameter (60,±,10),nm). Physical and spectroscopic (XAFS) measurements, together with XRD analysis, indicate that the silver nanoparticles in both , and , are crystalline with lattice parameters similar to bulk silver; however, the magnetic susceptibilities differ from bulk silver. [source] Synthesis and light-emitting properties of carbazole-based copolymers bearing cyano-substituted arylenevinylene chromophoreJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2010Koji Takagi Abstract Two arylenevinylene compounds bearing the cyano group at ,-position (6) and ,-position (9) from the dialkoxylphenylene unit were synthesized, in which the molecular termini were functionalized with 3-bromocarbazole. The Suzuki coupling copolymerization of these compounds with 1,4-bis[(3,-bromocarbazole-9,-yl)methylene]-2,5-didecyloxybenzene and 9,9-dihexylfluorene-2,7-bis(boronic acid) was carried out to obtain copolymers (cp67 and cp97) containing the cyano-substituted arylenevinylene fluorophore of 7 mol %. Model compounds (6, and 9,) corresponding to the arylenevinylene fluorophore were also prepared. The UV spectra of copolymers resembled that of homopolymer hp with no arylenevinylene segment in both CHCl3 solution and thin film. The emission maxima of copolymers in CHCl3 (394 nm) agreed with that of homopolymer indicating that the emission bands originated from the carbazole-fluorene-carbazole segment. The emission maximum wavelength of copolymer cp67 in thin film (477 nm) indicated fluorescence from the cyano-substituted arylenevinylene fluorophore because of the occurrence of fluorescence resonance electron transfer. In contrast, copolymer cp97 showed fluorescence at 528 nm to suggest the formation of a new emissive species such as a charge-transfer complex (exciplex). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 91,98, 2010 [source] Cationic Dye,sensitized Degradation of Sodium Hyaluronate Through Photoinduced Electron Transfer in the Upper Excited State,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2001Masanobu Kojima ABSTRACT The formation of ground-state complexes of methylene blue (MB) and thionine (TN) with sodium hyaluronate (NaHA) was clearly observed by means of absorption spectra in aqueous solution. Irradiation of the complexes using 313 nm light caused significant degradation of NaHA under oxygen and argon. However, the use of visible light over 400 nm, which gives the lowest excited singlet state of the cationic dyes, caused no degradation. MB and TN were more efficient sensitizers for the degradation of NaHA than rose bengal (RB), although RB is a more efficient singlet oxygen (1O2) sensitizer than the cationic dyes. Under similar conditions the polysaccharides with carboxyl groups, such as alginic acid and polygalacturonic acid, also photodecomposed. However, the polysaccharides without carboxyl groups, such as pullulan and methyl cellulose, did not. The irradiation of the polysaccharides in the presence of powdered titanium dioxide as a photocatalyst to generate the hydroxyl radical (·OH) in aerated aqueous solution caused the fragmentation of all the polymers. It was confirmed that methyl viologen, an electron-accepting sensitizer, formed a charge-transfer complex with NaHA, the irradiation of which caused the efficient degradation of NaHA. In the presence of ,- and ,-cyclodextrins the MB- and TN-sensitized photodegradation of NaHA was markedly suppressed. This was probably due to the formation of the inclusion complexes comprising the cationic dyes and the cyclodextrins. On the basis of the results obtained we propose that the cationic dye,sensitized degradation of NaHA involves a photoinduced electron-transfer process between the upper excited dyes and the ground-state NaHA and that ·OH and 1O2 do not participate in the degradation. [source] Synthetic Molecular Machine Based on Reversible End-to-Interior and End-to-End Loop Formation Triggered by Electrochemical StimuliCHEMISTRY - AN ASIAN JOURNAL, Issue 8-9 2008Jae Wook Lee Dr. Abstract We have designed and synthesized a novel [2]pseudorotaxane-based molecular machine in which the interconversion between end-to-interior and end-to-end loop structures is reversibly controlled by electrochemical stimuli. Cucurbit[8]uril (CB[8]) and the thread molecule 34+ with an electron-rich hydroxynaphthalene unit and two electron-deficient viologen units form the 1:1 complex 44+ with an end-to-interior loop structure, which is reversibly converted into an end-to-end structure upon reduction. Large changes in shape and size of the molecule accompany the reversible redox process. The key feature of the machine-like behavior is the reversible interconversion between an intramolecular charge-transfer complex and viologen cation radical dimer inside CB[8] triggered by electrochemical stimuli. [source] Spectroscopic and Electrochemical Evaluation of Salt Effects on Electron-Transfer Equilibria between Donor/Acceptor and Ion-Radical Pairs in Organic SolventsCHEMPHYSCHEM, Issue 16 2008Sergiy V. Rosokha Dr. Abstract Addition of "inert" tetrabutylammonium hexafluorophosphate (Bu4NPF6) to a solution of TMDO/DDQ in dichloromethane (where TMDO=2,2,6,6-tetramethylbenzo[1,2-d;4,5-d]bis[1,3]-dioxole, donor, and DDQ=diclorodicyano-p-benzoquinone, acceptor) is accompanied by drastic changes in the electronic spectrum, which are related to the appearance of the DDQ,. and TMDO+. ion radicals and a decrease in the concentration of the neutral molecules and the charge-transfer complex [TMDO,DDQ]. These changes point to a considerable rise (of about three orders of magnitude) in the apparent electron-transfer equilibrium constant (KET) for this donor/acceptor pair upon increasing the electrolyte concentration from 0 to 0.5,M. Accordingly, the ion-radical fractions and KET values are higher in dichloromethane, at high electrolyte concentrations, than in acetonitrile (where the effect of Bu4NPF6 is less pronounced). Similar trends of the apparent equilibrium constants are observed for the tetramethyl-p-phenylenediamine/tetracyanoethylene pair. Electron-transfer equilibrium constants for both donor/acceptor dyads obtained from spectral measurements are related to those derived from the redox potentials of the reactants. The effects of media variations on the electron-transfer equilibria are discussed within the ion-pairing and ionic-activity frameworks. [source] Detection of Explosives Using Field-Effect TransistorsELECTROANALYSIS, Issue 20 2009Etery Sharon Abstract The gate surfaces of ion-sensitive field-effect transistor (ISFET) devices were functionalized with the ,-donor units, 6-hydroxydopamine (1) or 4-aminothiophenol (2). Concentration of trinitrotoluene, TNT, on the gate via ,-donor-acceptor interactions yields charge-transfer complexes that alter the gate potential. This enables the label-free analysis of TNT with a detection limit corresponding to 1×10,7,M. [source] Synthesis and structural analysis of 1,4-bis[n -(N,N -dimethylamino)phenyl]buta-1,3-diynes and charge-transfer complexes with TCNEJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2001J. Gonzalo Rodríguez Abstract n -(N,N -Dimethylamino)phenylethynes were satisfactorily prepared by a Wittig reaction between chloromethylene(triphenyl)phosphine ylide and the appropriate n -(N,N -dimethylamino)benzaldehyde, followed by dehydrochlorination with a strong base. The conjugate dimers 1,4-bis[n -(N,N -dimethylamino)phenyl]buta-1,3-diyne were obtained by oxidative dimerization with copper(I) chloride. X-ray molecular structure analysis of the dimer 1,4-bis[2 -(N,N -dimethylamino)phenyl]buta-1,3-diyne corroborated the resonance contribution of the o -dimethylamino substituent, which was confirmed in the solid state by the molecular crystalline packing. Both o - and p -(N,N -dimethylamino) conjugate dimers develop 1:1 charge-transfer complexes with TCNE and their structure was identified by NMR, IR and UV,visible spectroscopic data. Differential scanning calorimetric analyses of the 1,3-diynes showed an irreversible transformation to a thermopolymer as a unimolecular reaction. Copyright © 2001 John Wiley & Sons, Ltd. [source] "Charge transfer" polymerization,and the absence thereof!JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2001H. K. Hall Abstract Mechanisms for "charge-transfer" spontaneous polymerizations and cycloadditions between electron-rich olefins and electron-poor olefins were reviewed. As for propagation, literature proposals involving charge-transfer complexes were rejected. Instead, alternating copolymerization is ascribed to polar effects in free-radical reactions. As for spontaneous initiation, literature proposals involving charge-transfer complexes, with or without proton transfer, were rejected. Instead, the initiating species is postulated to be a tetramethylene zwitterion biradical, which may initiate either ionic homopolymerization or free-radical copolymerization. A new hypothesis proposes that any interaction that brings vinyl monomers close together may facilitate tetramethylene formation and spontaneous polymerization. These interactions include Coulombic, acid,base, hydrophobic,hydrophilic and templating,tethering interactions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2069,2077, 2001 [source] New scope for synthesis of divinyl ether and maleic anhydride copolymer with narrow molecular mass distribution,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10-12 2002I. F. Volkova Abstract The alternating copolymer of divinyl ether and maleic anhydride (DIVEMA) possesses diverse biological activity and uses for production of drug delivery systems. DIVEMA's biological effects are determined by molecular mass, therefore it is necessary to have information about copolymer molecular mass and its distribution. A direct method for gel permeation chromatography analysis of DIVEMA molecular mass characteristics in aqua solution without any preliminary modification was developed. The effect of a number of factors (the concentration of monomers and their ratios, the concentration of initiator, the nature of the solvents) on DIVEMA's solution properties and molecular mass distribution was studied by gel permeation chromatography and viscometry. The approach to synthesis of DIVEMA with narrow molecular mass distribution was designed. The substantial influence of water on DIVEMA molecular mass characteristics was determined. The proposal was made that water may play a part in the formation of charge-transfer complexes playing a significant role in copolymerization. Copyright © 2003 John Wiley & Sons, Ltd. [source] Characterization of tetrathiofulvalene compounds using matrix-assisted laser desorption/ionization time-of-flight mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2001Shaoxiang Xiong Tetrathiofulvalene compounds are important components of charge-transfer complexes, which may be applied in various fields of scientific research and practical applications. Some of these compounds cannot be characterized by mass spectrometry. Here, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was used for the characterization of tetrathiofulvalenes. The samples could be easily desorbed and ionized to form singly charged ions, and mass spectra with isotopic resolution readily obtained. The mass spectrometric results for 26 compounds have shown that MALDI-TOF is more effective and convenient than other mass spectrometry methods, and resolves the problem of mass spectrometric characterization of tetrathiofulvalene compounds. Copyright © 2001 John Wiley & Sons, Ltd. [source] Electroluminescent Diodes from Complementary Discotic BenzoperylenesCHEMPHYSCHEM, Issue 9 2003Sonia Alibert-Fouet Dr. Unequal brothers: Benzoperylene carboxylic acid derivatives with flexible chains not only form charge-transporting columnar liquid crystals (see graphic), their charge-transport properties can also be tuned to be either of n - or of p -type: relatively minor changes in the substitution pattern yield different materials that are complementary enough to form red-fluorescent charge-transfer complexes and p,n junction electronic devices. [source] | |||||||||||||