Editing Optical brightener (section)

==Properties==
The most common classes of compounds with this property are the [[(E)-Stilbene|stilbenes]], e.g., [[4,4′-Diamino-2,2′-stilbenedisulfonic acid|4,4′-diamino-2,2′-stilbenedisulfonic acid]]. Older, non-commercial [[fluorescence|fluorescent]] compounds include [[umbelliferone]], which absorbs in the [[Ultraviolet|UV]] portion of the spectrum and re-emit it in the blue portion of the visible spectrum.  A white surface treated with an optical brightener can emit more visible light than that which shines on it, making it appear brighter. The blue light emitted by the brightener compensates for the diminishing blue of the treated material and changes the hue away from yellow or brown and toward white.<ref name=U2>{{Ullmann|first1=Eduard|last1=Smulders|first2=Eric|last2=Sung|title=Laundry Detergents, 2. Ingredients and Products|doi=10.1002/14356007.o15_013}}</ref>

[[File:Diaminostilbene disulfonic acid.svg|thumb|right|[[4,4′-Diamino-2,2′-stilbenedisulfonic acid|4,4′-diamino-2,2′-stilbenedisulfonic acid]] is a popular optical brightener.]]
[[File:2 5-bis(benzoxazol-2-yl)thiophene.svg|thumb|right|4,4'-bis(benzoxazolyl)-cis-stilbene and 2,5-bis(benzoxazol-2-yl)thiophene (shown here) are also intensely fluorescent and used as optical brighteners, e.g., in laundry detergents.<ref>M. Amine Fourati, Thierry Maris, W. G. Skene, C. Géraldine Bazuin, and Robert E. Prud’homme "Photophysical, Electrochemical and Crystallographic Investigations of the Fluorophore 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene" J. Phys. Chem. B, 2011, volume 115, 12362–12369.{{doi|10.1021/jp207136k}}</ref>]]

Approximately 400 brightener types are listed in the international [[Colour Index International|Colour Index]] database,<ref name="ColourIndex2021">{{cite web |title=Welcome to the Colour Index |url=https://colour-index.com/ |website=Colour Index |publisher=Society of Dyers and Colourists & American Association of Textile Chemists and Colourists |access-date=3 September 2021}}</ref> but fewer than 90 are produced commercially, and only a handful are commercially important. The Colour Index Generic Names and Constitution Numbers can be assigned to a specific substance. However, some are duplicated, since manufacturers apply for the index number when they produce it. The global OBA production for paper, textiles, and detergents is dominated by just a few di- and tetra-sulfonated triazole-stilbenes and a di-sulfonated stilbene-biphenyl derivatives. The stilbene derivatives are subject to fading upon prolonged exposure to UV, due to the formation of optically inactive cis-stilbenes. They are also degraded by oxygen in air, like most dye colorants. All brighteners have extended conjugation and/or aromaticity, allowing for electron movement. Some non-stilbene brighteners are used in more permanent applications such as whitening synthetic fiber.

Brighteners can be "boosted" by the addition of certain [[polyols]], such as high molecular weight [[polyethylene glycol]] or [[polyvinyl alcohol]]. These additives increase the visible blue light emissions significantly. Brighteners can also be "quenched". Excess brightener will often cause a greening effect as emissions start to show above the blue region in the visible spectrum.