Pyrene is a

polycyclic aromatic hydrocarbon A Polycyclic aromatic hydrocarbon (PAH) is any member of a class of organic compounds that is composed of multiple fused aromatic rings. Most are produced by the incomplete combustion of organic matter— by engine exhaust fumes, tobacco, incine ...

(PAH) consisting of four fused

benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

rings, resulting in a flat

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

system. The chemical formula is . This yellow-green solid is the smallest peri-fused PAH (one where the rings are fused through more than one face). Pyrene forms during

incomplete combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...

of organic compounds.

Occurrence and properties

Pyrene was first isolated from

coal tar Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas from coal. It is a type of creosote. It has both medical and industrial uses. Medicinally it is a topical medication applied to skin to treat psoria ...

, where it occurs up to 2% by weight. As a peri-fused PAH, pyrene is much more resonance-stabilized than its five-member-ring containing isomer fluoranthene. Therefore, it is produced in a wide range of combustion conditions. For example, automobiles produce about 1 μg/km.Senkan, Selim and Castaldi, Marco (2003) "Combustion" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim.

Reactions

Oxidation with chromate affords perinaphthenone and then naphthalene-1,4,5,8-tetracarboxylic acid. Pyrene undergoes a series of

hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or Saturated ...

reactions and is susceptible to halogenation, Diels-Alder additions, and nitration, all with varying degrees of selectivity. Bromination occurs at one of the 3-positions. Reduction with sodium affords the radical anion. From this anion, a variety of pi-arene complexes can be prepared.

Photophysics

Pyrene and its derivatives are used commercially to make

dye Juan de Guillebon, better known by his stage name DyE, is a French musician. He is known for the music video of the single "Fantasy Fantasy is a genre of speculative fiction that involves supernatural or Magic (supernatural), magical ele ...

s and dye precursors, for example pyranine and naphthalene-1,4,5,8-tetracarboxylic acid. It has strong absorbance in UV-Vis in three sharp bands at 330 nm in DCM. The emission is close to the absorption, but moving at 375 nm. The morphology of the signals change with the solvent. Its derivatives are also valuable molecular probes via

fluorescence Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with colore ...

spectroscopy, having a high quantum yield and lifetime (0.65 and 410 nanoseconds, respectively, in

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

at 293 K). Pyrene was the first molecule for which excimer behavior was discovered. Such excimer appears around 450 nm. Theodor Förster reported this in 1954.

Applications

Pyrene's fluorescence

emission spectrum The emission spectrum of a chemical element or chemical compound is the Spectrum (physical sciences), spectrum of frequencies of electromagnetic radiation emitted due to electrons making a atomic electron transition, transition from a high energ ...

is very sensitive to solvent polarity, so pyrene has been used as a probe to determine solvent environments. This is due to its excited state having a different, non-planar structure than the ground state. Certain emission bands are unaffected, but others vary in intensity due to the strength of interaction with a solvent. Pyrene-numbering

Pyrenes are strong electron donor materials and can be combined with several materials in order to make electron donor-acceptor systems which can be used in energy conversion and light harvesting applications.

Safety and environmental factors

Although it is not as problematic as

benzopyrene A benzopyrene is an organic compound with the formula C20H12. Structurally speaking, the colorless isomers of benzopyrene are pentacyclic hydrocarbons and are fusion products of pyrene and a phenylene group. Two isomeric species of benzopyrene ...

animal studies Animal studies is a recently recognised field in which animals are studied in a variety of cross-disciplinary ways. Scholars who engage in animal studies may be formally trained in a number of diverse fields, including art history, anthropology ...

have shown pyrene is

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...

to the

kidneys In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and right in the retro ...

and

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

. It is now known that pyrene affects several living functions in fish and algae. Its biodegradation has been heavily examined. The process commences with dihydroxylation at each of two kinds of CH=CH linkages. Experiments in pigs show that urinary 1-hydroxypyrene is a metabolite of pyrene, when given orally.

Occurrence and properties

Reactions

Photophysics

Applications

Safety and environmental factors

See also

References

Cited sources

Further reading