Editing Optical brightener

{{short description|Chemical compounds that absorb and re-emit light}}
[[Image:LaundrydetergentGlow.jpg|thumb|right|Laundry detergent [[fluorescing]] under ultraviolet light]]
'''Optical brighteners''', '''optical brightening agents''' ('''OBAs'''), '''fluorescent brightening agents''' ('''FBAs'''), or '''fluorescent whitening agents''' ('''FWAs'''),  are chemical compounds that absorb light in the [[ultraviolet]] and violet region (usually 340-370&nbsp;nm) of the [[electromagnetic spectrum]], and re-emit light in the blue region (typically 420-470&nbsp;nm) through the phenomenon of [[fluorescence]]. These additives are often used to enhance the appearance of color of [[textile|fabric]] and [[paper]], causing a "whitening" effect; they make intrinsically yellow/orange materials look less so, by compensating the deficit in blue and purple light reflected by the material, with the blue and purple optical emission of the fluorophore.<ref name=Ullmann>{{Ullmann|first1=Eduard|last1=Smulders|first2=Wolfgang|last2=Rybinski|first3=Eric|last3=Sung|first4=Wilfried|last4= Rähse|first5=Josef|last5=Steber|first6=Frederike |last6=Wiebel|first7= Anette|last7=Nordskog|title=Laundry Detergents|year=2002|doi=10.1002/14356007.a08_315.pub2}}</ref>

==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.

==Common uses==
Brighteners are commonly added to [[laundry detergent]]s to make the clothes appear cleaner.  Normally cleaned laundry appears yellowish, which consumers do not like.<ref name=U2/>  Optical brighteners have replaced [[Bluing (fabric)|bluing]] which was formerly used to produce the same effect.

Brighteners are used in many papers, especially high brightness papers, resulting in their strongly fluorescent appearance under UV illumination.  Paper brightness is typically measured at 457&nbsp;nm, well within the fluorescent activity range of brighteners.<ref>{{cite web |author1=Printer Technical Service |title=Understanding Paper Brightness |url=https://cdn-s3.sappi.com/s3fs-public/sappietc/Understanding%20Paper%20Brightness.pdf |website=sappi/etc |access-date=5 November 2018}}</ref> Paper used for banknotes does not contain optical brighteners, so a common method for detecting [[counterfeit]] notes is to check for fluorescence.

Optical brighteners have also found use in [[cosmetics]].  One application is to formulas for washing and conditioning grey or blonde hair, where the brightener can not only increase the luminance and sparkle of the hair, but can also correct dull, yellowish discoloration without darkening the hair.  Some advanced face and eye powders contain optical brightener [[microsphere]]s that brighten shadowed or dark areas of the skin, such as "tired eyes".

End uses of optical brighteners include:
# Detergent whitener (instead of bluing agents)
# [[paper chemicals|Paper brightening]] ([[sizing|internal]] or in a [[coated paper|coating]])
# Fiber whitening (internal, added to polymer melts)
# Textile whitening (external, added to [[textile finishing|fabric finishes]])
# Color-correcting or brightening additive in advanced [[Cosmetics|cosmetic]] formulas ([[shampoo]]s, conditioners, eye makeup)

==Misuse==
From around 2002 to 2012, chemical brighteners were used by many [[Chinese people|Chinese]] farmers to enhance the appearance of their white mushrooms. This illegal use was mostly eliminated by the Chinese Ministry of Agriculture.<ref name="Hoorfar 2014 p. 401">{{cite book | last1=Hoorfar | first1=J. |last2=Xing |first2=Z. |last3=Zhao |first3=X. | title=Global Safety of Fresh Produce: A Handbook of Best Practice, Innovative Commercial Solutions and Case Studies | publisher=Elsevier Science | series=Woodhead Publishing Series in Food Science, Technology and Nutrition | year=2014 | isbn=978-1-78242-027-9 | url=https://books.google.com/books?id=IpniAgAAQBAJ&pg=PA401 | access-date=Jan 27, 2020 | page=401}}</ref>

==References==
{{Reflist}}
* {{Britannica|430363|Optical brightener (chemical compound)}}
{{Paper}}

{{DEFAULTSORT:Optical Brightener}}
[[Category:Fluorescent dyes]]
[[Category:Cleaning product components]]
[[Category:Luminescence]]
[[Category:Papermaking]]
[[Category:Process chemicals]]