|
Charge-transfer Complex
In chemistry, charge-transfer (CT) complex, or electron donor-acceptor complex, describes a type of supramolecular assembly of two or more molecules or ions. The assembly consists of two molecules that self-attract through electrostatic forces, i.e., one has at least partial negative charge and the partner has partial positive charge, referred to respectively as the electron acceptor and electron donor. In some cases, the degree of charge transfer is "complete", such that the CT complex can be classified as a salt. In other cases, the charge-transfer association is weak, and the interaction can be disrupted easily by polar solvents. Examples Electron donor-acceptor complexes A number of organic compounds form charge-transfer complex, which are often described as electron-donor-acceptor complexes (EDA complexes). Typical acceptors are nitrobenzenes or tetracyanoethylene (TCNE). The strength of their interaction with electron donors correlates with the ionization potential ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ECW Model
In chemistry, the ECW model is a semi-quantitative model that describes and predicts the strength of Lewis acid–Lewis base interactions. Many chemical reactions can be described as acid–base reactions, so models for such interactions are of potentially broad interest. The model initially assigned E and C parameters to each and every acid and base. The model was later expanded to ''the ECW model'' to cover reactions that have a constant energy term, ''W'', which describes processes that precede the acid–base reaction. This quantitative model is often discussed with the qualitative HSAB theory, which also seeks to rationalize the behavior of diverse acids and bases. History of the problem As early as 1938, G. N. Lewis pointed out that the relative strength of an acid or base depended upon the base or acid against which it was measured. No single rank order of acid or base strength can predict the energetics of the cross reaction. Consider the following pair of acid–base re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Conductor (material)
In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. The flow of negatively charged electrons generates electric current, positively charged holes, and positive or negative ions in some cases. In order for current to flow within a closed electrical circuit, one charged particle does not need to travel from the component producing the current (the current source) to those consuming it (the loads). Instead, the charged particle simply needs to nudge its neighbor a finite amount, who will nudge ''its'' neighbor, and on and on until a particle is nudged into the consumer, thus powering it. Essentially what is occurring is a long chain of momentum transfer between mobile charge carriers; the Drude model of conduction describes this process more rigorously. This momentum transfer model makes metal an ideal choice fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solid State Communications
Solid State Communications is a peer-reviewed scientific journal of solid-state physics. The journal specializes in short papers on significant developments in the condensed matter science. The journal was established 1963, when the ''Journal of Physics and Chemistry of Solids'' split its letters section to create this journal. Elias Burstein served as founding chief editor until 1992, and was succeeded by Manuel Cardona until 2004, when Aron Pinczuk assumed the role. Pinczuk stepped down in 2020. The journal is published bimonthly by Elsevier and its current editor-in-chief is François Peeters (University of Antwerp). Abstracting and Indexing The journal is abstracted and indexing in the following databases: *Cambridge Scientific Abstracts *Chemical Abstracts *Current Contents/Physics, Chemical, & Earth Sciences *Current Contents/ SciSearch Database *Current Contents/Social & Behavioral Sciences *MSCI *Engineering Index *INSPEC * PASCAL/CNRS *Research Alert * SSSA/ CISA/ EC ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetrathiafulvalene
Tetrathiafulvalene (TTF) is an organosulfur compound with the formula . It is the parent of many tetrathiafulvenes. Studies on these heterocyclic compound contributed to the development of molecular electronics, although no practical applications of TTF emerged. TTF is related to the hydrocarbon fulvalene () by replacement of four CH groups with sulfur atoms. Over 10,000 scientific publications discuss TTF and its derivatives. Preparation The high level of interest in TTFs spawned many syntheses of TTF and its analogues. Most preparations entail the coupling of cyclic building blocks such as 1,3-dithiole-2-thion or the related 1,3-dithiole-2-ones. For TTF itself, the synthesis begins with the cyclic trithiocarbonate ( 1,3-dithiole-2-thione), which is ''S''-methylated and then reduced to give (1,3-dithiole-2-yl methyl thioether), which is treated as follows: Protonolysis of a thioether: : Followed by deprotonation of the dithiolium cation with triethylamine: : Redox prop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TCNQ
Tetracyanoquinodimethane (TCNQ) is an organic compound with the chemical formula . It is an orange crystalline solid. This cyanocarbon, a relative of para-quinone, is an electron acceptor that is used to prepare charge transfer salts, which are of interest in molecular electronics. Preparation and structure TCNQ is prepared by the condensation of 1,4-cyclohexanedione with malononitrile, followed by dehydrogenation of the resulting diene with bromine: : : The molecule is planar, with D2h symmetry. Reactions Like tetracyanoethylene (TCNE), TCNQ is easily reduced to give a blue-coloured radical anion. The reduction potential is about −0.3 V relative to the ferrocene/ ferrocenium couple. This property is exploited in the development of charge-transfer salts. TCNQ also forms complexes with electron-rich metal complexes. Charge transfer salts TCNQ achieved great attention because it forms charge-transfer salts with high electrical conductivity. These discoveries were influe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bromine
Bromine is a chemical element; it has chemical symbol, symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between those of chlorine and iodine. Isolated independently by two chemists, Carl Jacob Löwig (in 1825) and Antoine Jérôme Balard (in 1826), its name was derived , referring to its sharp and pungent smell. Elemental bromine is very reactive and thus does not occur as a free element in nature. Instead, it can be isolated from colourless soluble crystalline mineral halide Ionic salt, salts analogous to table salt, a property it shares with the other halogens. While it is rather rare in the Earth's crust, the high solubility of the bromide ion (Br) has caused its Bromine cycle, accumulation in the oceans. Commercially the element is easily extracted from brine evaporation ponds, mostly in the United States and Israel. The mass of bromine in the oce ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perylene
Perylene or perilene is a polycyclic aromatic hydrocarbon with the chemical formula C20H12, occurring as a brown solid. It or its derivatives may be carcinogenic, and it is considered to be a hazardous pollutant. In cell membrane cytochemistry, perylene is used as a fluorescent lipid probe. It is the parent compound of a class of rylene dyes. Reactions Like other polycyclic aromatic compounds, perylene is reduced by alkali metals to give a deeply colored radical anion and a dianion. The diglyme solvates of these salts have been characterized by X-ray crystallography. Emission Perylene displays blue fluorescence. It is used as a blue-emitting dopant material in OLEDs, either pure or substituted. Perylene can also be used as an organic photoconductor. It has an absorption maximum at 434 nm, and as with all polycyclic aromatic compounds, low water solubility (1.2 x 10−5 mmol/L). Perylene has a molar absorptivity of 38,500 M−1cm−1 at 435.7 nm. Image:Peryle ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sizing
Sizing or size is a substance that is applied to, or incorporated into, other materials—especially papers and textiles—to act as a protective filler or glaze. Sizing is used in papermaking and textile manufacturing to change the absorption and wear characteristics of those materials. Sizing is used for oil-based surface preparation for gilding (sometimes called ''mordant'' in this context). It is used by painters and artists to prepare paper and textile surfaces for some art techniques. Sizing is used in photography to increase the sharpness of a print, to change the glossiness of a print, or for other purposes depending on the type of paper and printing technique. Fibers used in composite materials are treated with various sizing agents to promote adhesion with the matrix material. Sizing is used during paper manufacture to reduce the paper's tendency when dry to absorb liquid, with the goal of allowing inks and paints to remain on the surface of the paper and to dry t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Charge-transfer Band
image:Tris(bipyridine)ruthenium(II)-chloride-powder.jpg, 193px, The intense color of tris(bipyridine)ruthenium(II) arises from a metal-to-ligand charge-transfer band. Charge-transfer bands are a characteristic feature of the optical spectra of many compounds. These bands are typically more intense than d–d transitions. They typically exhibit solvatochromism, consistent with shifts of electron density that would be sensitive to solvation. CT absorptions bands are intense and often lie in the ultraviolet or visible portion of the spectrum. For coordination complexes, charge-transfer bands often exhibit molar absorptivities, ε, of about 50000 L mol−1 cm−1. By contrast ε values for d–d transitions are in the range of 20–200 L mol−1 cm−1. CT transitions are spin-allowed and Laporte rule, Laporte-allowed. The weaker d–d transitions are potentially spin-allowed but always Laporte-forbidden. Charge-transfer bands of transition metal complexes result from shift of cha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
