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(Z)-Stilbene
(''Z'')-Stilbene is a diarylethene, that is, a hydrocarbon consisting of a cis ethene double bond substituted with a phenyl group on both carbon atoms of the double bond. The name stilbene was derived from the Greek word , which means shining. Isomers Stilbene exists as two possible isomers known as (''E'')-stilbene and (''Z'')-stilbene. (''Z'')-Stilbene is sterically hindered and less stable because the steric interactions force the aromatic rings 43° out-of-plane and prevent conjugation. (''Z'')-Stilbene has a melting point of , while (''E'')-stilbene melts around , illustrating that the two compounds are quite different. Uses * Stilbene is used in manufacture of dyes and optical brighteners, and also as a phosphor and a scintillator. * Stilbene is one of the gain mediums used in dye lasers. Properties * Stilbene will typically have the chemistry of a diarylethene, a conjugated alkene. * Stilbene can undergo photoisomerization under the influence of UV light. * Stilbene ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
(E)-Stilbene
(''E'')-Stilbene, commonly known as ''trans''-stilbene, is an organic compound represented by the Structural formula#Condensed formulas, condensed structural formula CHCH=CHCH. Classified as a diarylethene, it features a central ethylene moiety (chemistry), moiety with one phenyl group substituent on each end of the carbon–carbon double bond. It has an (E), (''E'') stereochemistry, meaning that the phenyl groups are located on opposite sides of the double bond, the opposite of its geometric isomer, cis-stilbene, ''cis''-stilbene. ''Trans''-stilbene occurs as a white crystalline solid at room temperature and is highly soluble in organic solvents. It can be converted to ''cis''-stilbene photochemistry, photochemically, and further reacted to produce phenanthrene. Stilbene was discovered in 1843 by the French chemist Auguste Laurent. The name "stilbene" is derived from the Greek language, Greek word ''στίλβω'' (''stilbo''), which means "I shine", on account of the lust ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diarylethene
Diarylethene is the general name of a class of chemical compounds that have aromatic functional groups bonded to each end of a carbon–carbon double bond. The simplest example is stilbene, which has two geometric isomers, E and Z. Under the influence of light, these compounds can generally perform two kinds of reversible isomerizations: * E to Z isomerizations, most common for stilbenes (and azobenzenes). This process goes through an excited state energy minimum where the aromatic rings lie at 90° to each other. This conformation drops to the ground state and generally relaxes to trans and cis forms in a 1:1 ratio, thus the quantum yield for E-Z isomerization is very rarely greater than 0.5. *6π electrocyclizations of the Z form, leading to an additional bond between the two aryl functionalities and a disruption of the aromatic character of these groups.J. March, ''Advanced Organic Chemistry'', 4th ed. (1992). The quantum yield of this reaction is generally less than 0.1, and in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photoisomerization
In chemistry, photoisomerization is a form of isomerization induced by photoexcitation. Both reversible and irreversible photoisomerizations are known for photoswitchable compounds. The term "photoisomerization" usually, however, refers to a reversible process. Applications Photoisomerization of the compound retinal in the eye allows for vision. Photoisomerizable substrates have been put to practical use, for instance, in pigments for rewritable CDs, DVDs, and 3D optical data storage solutions. In addition, interest in photoisomerizable molecules has been aimed at molecular devices, such as molecular switches, molecular motors, and molecular electronics. Another class of device that uses the photoisomerization process is as an additive in liquid crystals to change their linear and nonlinear properties. Due to the photoisomerization is possible to induce a molecular reorientation in the liquid crystal bulk, which is used in holography, as spatial filter or optical switching. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Laser Gain Media
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radiation. The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories, based on theoretical work by Charles H. Townes and Arthur Leonard Schawlow and the optical amplifier patented by Gordon Gould. A laser differs from other sources of light in that it emits light that is ''coherent''. Spatial coherence allows a laser to be focused to a tight spot, enabling uses such as optical communication, laser cutting, and lithography. It also allows a laser beam to stay narrow over great distances (collimation), used in laser pointers, lidar, and free-space optical communication. Lasers can also have high temporal coherence, which permits them to emit light with a very narrow frequency spectrum. Temporal coherence can also ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphors And Scintillators
A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or visible light, and cathodoluminescent substances which glow when struck by an electron beam (cathode rays) in a cathode-ray tube. When a phosphor is exposed to radiation, the orbital electrons in its molecules are excited to a higher energy level; when they return to their former level they emit the energy as light of a certain color. Phosphors can be classified into two categories: fluorescent substances which emit the energy immediately and stop glowing when the exciting radiation is turned off, and phosphorescent substances which emit the energy after a delay, so they keep glowing after the radiation is turned off, decaying in brightness over a period of milliseconds to days. Fluorescent materials are used in applications in which t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fluorescent Dyes
A fluorophore (or fluorochrome, similarly to a chromophore) is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with several π bonds. Fluorophores are sometimes used alone, as a tracer in fluids, as a dye for staining of certain structures, as a substrate of enzymes, or as a probe or indicator (when its fluorescence is affected by environmental aspects such as polarity or ions). More generally they are covalently bonded to macromolecules, serving as a markers (or dyes, or tags, or reporters) for affine or bioactive reagents (antibodies, peptides, nucleic acids). Fluorophores are notably used to stain tissues, cells, or materials in a variety of analytical methods, such as fluorescent imaging and spectroscopy. Fluorescein, via its amine-reactive isothiocyanate derivative fluorescein isothiocyanate (FITC), has been one of the most popular fluorophores. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Luminescence
Luminescence is a spontaneous emission of radiation from an electronically or vibrationally excited species not in thermal equilibrium with its environment. A luminescent object emits ''cold light'' in contrast to incandescence, where an object only emits light after heating. Generally, the emission of light is due to the movement of electrons between different energy levels within an atom after excitation by external factors. However, the exact mechanism of light emission in vibrationally excited species is unknown. The dials, hands, scales, and signs of aviation and navigational instruments and markings are often coated with luminescent materials in a process known as ''luminising''. Types * Ionoluminescence, a result of bombardment by fast ions * Radioluminescence, a result of bombardment by ionizing radiation * Electroluminescence, a result of an electric current passed through a substance ** Cathodoluminescence, a result of a luminescent material being struck by elect ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pterostilbene
Pterostilbene () (trans-3,5-dimethoxy-4-hydroxystilbene) is a stilbenoid chemically related to resveratrol. In plants, it serves a defensive phytoalexin role. Natural occurrence Pterostilbene is found in almonds, various ''Vaccinium'' berries (including Blueberry, blueberries), grape leaves and vines. It is also encountered in the xylem, particularly in the heartwood of ''Pterocarpus marsupium'' as well as in other species of the ''Pterocarpus'' family, including Malay padauk, the Narra tree (''Pterocarpus indicus''), Muninga and African padauk (''Pterocarpus erinaceus''), thus contributing to the high natural durability as a known phytoalexin. Safety and regulation Pterostilbene is considered to be a corrosive substance, is dangerous upon exposure to the eyes, and is an environmental toxin, especially to aquatic life. A preliminary study of healthy human subjects given pterostilbene for 6–8 weeks, showed pterostilbene to be safe for human use at dosages up to 250 mg p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Resveratrol
Resveratrol (3,5,4′-trihydroxy-''trans''-stilbene) is a stilbenoid, a type of natural phenol or polyphenol and a phytoalexin produced by several plants in response to injury or when the plant is under attack by pathogens, such as bacterium, bacteria or fungus, fungi. Sources of resveratrol in food include the skin of grapes, blueberries, raspberries, mulberries, and peanuts. Although commonly used as a dietary supplement and studied in laboratory models of human diseases, there is no evidence-based medicine, high-quality evidence that resveratrol improves longevity, lifespan or has a substantial effect on any human disease. Research Resveratrol has been studied for its potential therapeutic use, with little evidence of anti-disease effects or health benefits in humans. Cardiovascular disease There is no evidence of benefit from resveratrol in people who already have heart disease. A 2018 meta-analysis found no effect on systolic blood pressure, systolic or diastolic blood pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stilbenoid
Stilbenoids are hydroxylated derivatives of stilbene. They have a C6–C2–C6 structure. In biochemical terms, they belong to the family of phenylpropanoids and share most of their biosynthesis pathway with Chalconoid, chalcones. Most stilbenoids are produced by plants, and the only known exception is the antimicrobial stilbenoid drug tapinarof which is biosynthesized by the Gram-negative bacterium ''Photorhabdus luminescens.'' Chemistry Stilbenoids are hydroxylated derivatives of stilbene and have a C6–C2–C6 structure. They belong to the family of phenylpropanoids and share most of their biosynthesis pathway with Chalconoid, chalcones. Under UV irradiation, stilbene and its derivatives undergo intramolecular cyclization, called stilbene photocyclization to form dihydrophenanthrenes. Oligomeric forms are known as oligostilbenoids. Types ;Aglycones * Piceatannol in the roots of Norway spruces * Pinosylvin is a fungal toxin protecting wood from fungal infection, found in t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrocyclic Reaction
In organic chemistry, an electrocyclic reaction is a type of pericyclic reaction, pericyclic, rearrangement reaction, rearrangement reaction where the net result is one pi bond being converted into one sigma bond or vice versa. These reactions are usually categorized by the following criteria: * Reactions can be either photochemistry, photochemical or thermal. * Reactions can be either ring-opening or ring-closing (electrocyclization). * Depending on the type of reaction (Organic photochemistry, photochemical or thermal) and the number of pi electrons, the reaction can happen through either a conrotatory and disrotatory, conrotatory or disrotatory mechanism. * The type of rotation determines whether the cis–trans isomerism, cis or trans isomer of the product will be formed. Classical examples The Nazarov cyclization reaction is a named electrocyclic reaction converting divinylketones to cyclopentenones. A classic example is the thermal ring-opening reaction of 3,4-dimethylcyclo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intramolecular Reaction
In chemistry, intramolecular describes a Chemical process, process or characteristic limited within the Chemical structure, structure of a single molecule, a property or phenomenon limited to the extent of a single molecule. Relative rates In intramolecular organic reactions, two reaction sites are contained within a single molecule. This configuration elevates the effective concentration of the reacting partners resulting in high reaction rates. Many intramolecular reactions are observed where the intermolecular version does not take place. Intramolecular reactions, especially ones leading to the formation of 5- and 6-membered rings, are rapid compared to an analogous intermolecular process. This is largely a consequence of the reduced entropic cost for reaching the transition state of ring formation and the absence of significant strain associated with formation of rings of these sizes. For the formation of different ring sizes via cyclization of substrates of varying tether ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
