Optical brightener
Encyclopedia
Optical brighteners, optical brightening agents (OBAs), fluorescent brightening agents (FBAs) or fluorescent whitening agents (FWAs) are dye
s that absorb light in the ultraviolet
and violet region (usually 340-370 nm) of the electromagnetic spectrum
, and re-emit light in the blue region (typically 420-470 nm). Fluorescent activity is a short term or rapid emission response, unlike phosphorescence, which is a delayed emission. These additives are often used to enhance the appearance of color of fabric and paper
, causing a "whitening" effect, making materials look less yellow by increasing the overall amount of blue light reflected.
and older, non-commercial fluorescent
chemical such as umbelliferone
, which absorb energy in the 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.
There are approximately 400 brightener types listed in the Color Index, but less than 90 are actually produced commercially and only a handful are commercially important. Generically, the C.I. FBA number can be assigned to a specific molecule, 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. These are subject to fading when exposed long term to UV, due to the formation of optically inactive stilbene cis-isomers found at the center of the molecule. Exposed to gases and especially oxygen they will fade too, like most dye colorants. All brighteners have extended conjungation and/or aromaticity, allowing for electron movement. Some non-stilbene brighteners are used in more permanent applications such as whitening synthetic fiber.
Basic class types of brighteners include:
Brighteners can be "boosted" by the addition of certain polyols like high molecular weight polyethylene glycol
or polyvinyl alcohol
. These additives increase the visible blue light emissions significantly. Brighteners can also be "quenched". Too much use of brightener will often cause a greening effect as emissions start to show above the blue region in the visible spectrum. Besides the formation of cis isomer in stilbene-containing brighteners (only the trans isomer is optically active), continued exposure to UV-containing light will actually cleave the molecule and start the process of degradation.
detergent
s to replace whitening agents removed during washing and to make the clothes appear cleaner. Optical brighteners have replaced bluing
which was formerly used to produce the same effect. Some brighteners can cause allergic reactions when in contact with skin, depending on the individual.
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 nm, well within the fluorescent activity range of brighteners. 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".
A side effect of textile optical whitening is to make the treated fabrics more visible with Night Vision Devices than non-treated ones. This may or may not be desirable for military or other applications. Optically brightened paper is often not useful in exacting photographic or art applications, since the whiteness decreases with time.
Enduses of optical brighteners include:
Dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
s that absorb light in the ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
and violet region (usually 340-370 nm) of the electromagnetic spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
, and re-emit light in the blue region (typically 420-470 nm). Fluorescent activity is a short term or rapid emission response, unlike phosphorescence, which is a delayed emission. These additives are often used to enhance the appearance of color of fabric and paper
Paper
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
, causing a "whitening" effect, making materials look less yellow by increasing the overall amount of blue light reflected.
Properties
The most common classes of chemicals with this property are the stilbenes(Z)-Stilbene
-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 stilbos, which means shining....
and older, non-commercial fluorescent
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
chemical such as umbelliferone
Umbelliferone
Umbelliferone, also known as 7-hydroxycoumarin, hydrangine, skimmetine, and beta-umbelliferone, is a widespread natural product of the coumarin family. It occurs in many familiar plants from the Apiaceae family such as carrot, coriander and garden angelica, as well plants from other families such...
, which absorb energy in the UV
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
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.
There are approximately 400 brightener types listed in the Color Index, but less than 90 are actually produced commercially and only a handful are commercially important. Generically, the C.I. FBA number can be assigned to a specific molecule, 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. These are subject to fading when exposed long term to UV, due to the formation of optically inactive stilbene cis-isomers found at the center of the molecule. Exposed to gases and especially oxygen they will fade too, like most dye colorants. All brighteners have extended conjungation and/or aromaticity, allowing for electron movement. Some non-stilbene brighteners are used in more permanent applications such as whitening synthetic fiber.
Basic class types of brighteners include:
- Triazine-stilbenes (di-, tetra- or hexa-sulfonated)
- CoumarinCoumarinCoumarin is a fragrant chemical compound in the benzopyrone chemical class, found in many plants, notably in high concentration in the tonka bean , vanilla grass , sweet woodruff , mullein , sweet grass , cassia cinnamon and sweet clover...
s - ImidazolineImidazolineImidazoline is a nitrogen-containing heterocycle with formula C3H6N2, derived from imidazole. The ring contains an imine bond, and the carbons at the 4 and 5 positions are singly bonded, rather than doubly bonded for the case of imidazole...
s - DiazoleDiazoleDiazole refers to either one of a pair of isomeric chemical compounds with molecular formula C3H4N2, having a five-membered ring consisting of three carbon atoms and two nitrogen atoms.The two isomers are:...
s - TriazoleTriazoleTriazole refers to either one of a pair of isomeric chemical compounds with molecular formula C2H3N3, having a five-membered ring of two carbon atoms and three nitrogen atoms.The two isomers are:*1,2,3-Triazole 100px*1,2,4-Triazole 100px...
s - Benzoxazolines
- Biphenyl-stilbenes
Brighteners can be "boosted" by the addition of certain polyols like high molecular weight polyethylene glycol
Polyethylene glycol
Polyethylene glycol is a polyether compound with many applications from industrial manufacturing to medicine. It has also been known as polyethylene oxide or polyoxyethylene , depending on its molecular weight, and under the tradename Carbowax.-Available forms:PEG, PEO, or POE refers to an...
or polyvinyl alcohol
Polyvinyl alcohol
Polyvinyl alcohol is a water-soluble synthetic polymer .-Properties:...
. These additives increase the visible blue light emissions significantly. Brighteners can also be "quenched". Too much use of brightener will often cause a greening effect as emissions start to show above the blue region in the visible spectrum. Besides the formation of cis isomer in stilbene-containing brighteners (only the trans isomer is optically active), continued exposure to UV-containing light will actually cleave the molecule and start the process of degradation.
Common uses
Brighteners are commonly added to laundryLaundry
Laundry is a noun that refers to the act of washing clothing and linens, the place where that washing is done, and/or that which needs to be, is being, or has been laundered...
detergent
Detergent
A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...
s to replace whitening agents removed during washing and to make the clothes appear cleaner. Optical brighteners have replaced bluing
Bluing (fabric)
Bluing, laundry blue, or washing blue is a household product used to improve the appearance of textiles, especially white fabrics. Used during laundering, it adds a trace of blue dye to the fabric.- Uses :White fabrics acquire a slight color cast after use , because they can never be cleaned...
which was formerly used to produce the same effect. Some brighteners can cause allergic reactions when in contact with skin, depending on the individual.
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 nm, well within the fluorescent activity range of brighteners. Paper used for banknotes does not contain optical brighteners, so a common method for detecting counterfeit
Counterfeit
To counterfeit means to illegally imitate something. Counterfeit products are often produced with the intent to take advantage of the superior value of the imitated product...
notes is to check for fluorescence.
Optical brighteners have also found use in cosmetics
Cosmetics
Cosmetics are substances used to enhance the appearance or odor of the human body. Cosmetics include skin-care creams, lotions, powders, perfumes, lipsticks, fingernail and toe nail polish, eye and facial makeup, towelettes, permanent waves, colored contact lenses, hair colors, hair sprays and...
. 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
Microsphere
Microsphere are small spherical particles, with diameters in the micrometer range . Microspheres are sometimes referred to as microparticles....
s that brighten shadowed or dark areas of the skin, such as "tired eyes".
A side effect of textile optical whitening is to make the treated fabrics more visible with Night Vision Devices than non-treated ones. This may or may not be desirable for military or other applications. Optically brightened paper is often not useful in exacting photographic or art applications, since the whiteness decreases with time.
Enduses of optical brighteners include:
- Detergent whitener (instead of bluing agents)
- Paper brighteningPaper chemicals-Optical brightening agent:Optical brightener is used to make paper appear more white. Optical brightening agents use fluorescence to absorb invisible radiation from the ultraviolet part of the light spectrum and re-emit the radiation as light in the visible blue range. The optical brightening...
(internalSizingSizing or size is any one of numerous specific substances that is applied to or incorporated in other material, especially papers and textiles, to act as a protecting filler or glaze....
or in a coatingCoated paperCoated paper is paper which has been coated by a compound to impart certain qualities to the paper, including weight, surface gloss, smoothness or reduced ink absorbency. Kaolinite or calcium carbonate are used to coat paper for high quality printing used in packaging industry and in magazines...
) - Fiber whitening (internal, added to polymer melts)
- Textile whitening (external, added to fabric finishes)
- Color-correcting or brightening additive in advanced cosmeticCosmeticsCosmetics are substances used to enhance the appearance or odor of the human body. Cosmetics include skin-care creams, lotions, powders, perfumes, lipsticks, fingernail and toe nail polish, eye and facial makeup, towelettes, permanent waves, colored contact lenses, hair colors, hair sprays and...
formulas (shampooShampooShampoo is a hair care product used for the removal of oils, dirt, skin particles, dandruff, environmental pollutants and other contaminant particles that gradually build up in hair...
s, conditioners, eye makeup)