Leuco dye

A leuco dye is a dye whose molecules can acquire two forms, one of which is colorless.

For example, the spiro form of an oxazine is a colorless leuco dye; the conjugated system of the oxazine and another aromatic part of the molecule is separated by an sp3-hybridized "spiro" carbon. After protonating a part of the molecule, irradiation with UV light (see Photochromism), or introducing other kind of such change, the bond between the spiro carbon and the oxazine interrupts, the ring opens, the spiro carbon achieves sp2 hybridization and becomes planar, the aromatic group rotates, aligns its π-orbitals with the rest of the molecule, and a conjugated system forms, with ability to absorb photons of visible light, and therefore appear colorful.

Another example of a leuco dye is the crystal violet lactone, which in its lactone form is colorless or slightly yellowish, but in low pH, when it is protonated, it becomes intensely violet. Other examples are phenolphthalein and thymolphthalein, colorless in acidic to neutral pH, but becoming pink and blue in alkaline environment. Other example are many redox indicators, which undergo reversible color change between colored and colorless form at a specific electrode potential.

Leuco dyes are a key component of some thermochromic dyes and thermal printer papers, photochromic materials, and of the Flexplay DVD discs with limited play time, where e.g. leuco form of methylene blue is used.

Corporations that use Leuco Dyes

*Del Sol
*Flexplay
*hypercolor
*Phallacy Clothing
*Transitions lenses


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  • leuco dye — leukodažiklis statusas T sritis chemija apibrėžtis Bespalvė tirpi leukobazė, kuri oksiduojama ant dažomos medžiagos virsta spalvotu junginiu. atitikmenys: angl. leuco dye; vat dye rus. лейкокраситель …   Chemijos terminų aiškinamasis žodynas

  • leuco base — noun Etymology: International Scientific Vocabulary leuco + base : a colorless or weakly colored amine that is formed by reduction of a dye (as a triphenylmethane dye) or its carbinol derivative and that on oxidation and treatment with acids… …   Useful english dictionary

  • Dye — For other uses, see Dye (disambiguation). Yarn drying after being dyed in the early American tradition, at Conner Prairie living history museum. A dye is a colored substance that has an affinity to the substrate to which it …   Wikipedia

  • leuco ester — noun : a water soluble sodium salt of the sulfuric acid ester of the leuco compound of a vat dye that is applied to textiles and then oxidized in acid solution to the corresponding vat dye compare dye table I …   Useful english dictionary

  • leuco base — /looh koh/, Chem. a noncolored or slightly colored compound that is produced by reducing a dye and is readily oxidized to regenerate the dye. [1885 90; independent use of LEUCO ] * * * …   Universalium

  • leuco form — noun The colorless form of a dye created as a result of its insoluble form interacting with an alkaline liquor. Color returns to the dye upon oxidation …   Wiktionary

  • leuco base — /lukoʊ ˈbeɪs/ (say loohkoh bays) noun a colourless or slightly coloured compound made by reducing a dye and which is readily oxidised to regenerate the dye …   Australian English dictionary

  • dye base — noun : an organic base that is itself a dye or that with acids forms salts which are dyes called also color base; compare leuco base …   Useful english dictionary

  • leuco-base — leuˈco base or leuˈco compound noun A colourless reduction product of a dye that can be converted back to the dye by oxidation • • • Main Entry: ↑leuc …   Useful english dictionary

  • leuco-compound — leuˈco base or leuˈco compound noun A colourless reduction product of a dye that can be converted back to the dye by oxidation • • • Main Entry: ↑leuc …   Useful english dictionary


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