Pyrene

For other uses, see Pyrene (disambiguation).

Pyrene is a polycyclic aromatic hydrocarbon (PAH) consisting of four fused benzene rings, resulting in a flat aromatic system. The chemical formula is C₁₆H₁₀. 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 of organic compounds.^[10]

Pyrene

Names
Preferred IUPAC name Pyrene[1]
Other names Benzo[def]phenanthrene
Identifiers
CAS Number	129-00-0 Y
3D model (JSmol)	Interactive image
Beilstein Reference	1307225
ChEBI	CHEBI:39106 Y
ChEMBL	ChEMBL279564 Y
ChemSpider	29153 Y
ECHA InfoCard	100.004.481
Gmelin Reference	84203
KEGG	C14335 Y
PubChem CID	31423
RTECS number	UR2450000
UNII	9E0T7WFW93 Y
CompTox Dashboard (EPA)	DTXSID3024289
InChI InChI=1S/C16H10/c1-3-11-7-9-13-5-2-6-14-10-8-12(4-1)15(11)16(13)14/h1-10H Y Key: BBEAQIROQSPTKN-UHFFFAOYSA-N Y InChI=1/C16H10/c1-3-11-7-9-13-5-2-6-14-10-8-12(4-1)15(11)16(13)14/h1-10H Key: BBEAQIROQSPTKN-UHFFFAOYAB
SMILES c1cc2cccc3c2c4c1cccc4cc3
Properties
Chemical formula	C16H10
Molar mass	202.256 g·mol−1
Appearance	colorless solid (yellow impurities are often found at trace levels in many samples).
Density	1.271 g/cm3[2]
Melting point	150.62 °C (303.12 °F; 423.77 K)[2]
Boiling point	394 °C (741 °F; 667 K)[2]
Solubility in water	0.049 mg/L (0 °C) 0.139 mg/L (25 °C) 2.31 mg/L (75 °C)[3]
log P	5.08[4]
Band gap	2.02 eV[5]
Magnetic susceptibility (χ)	−147·10−6 cm3/mol[6]
Structure[7]
Crystal structure	Monoclinic
Space group	P21/a
Lattice constant	a = 13.64 Å, b = 9.25 Å, c = 8.47 Å α = 90°, β = 100.28°, γ = 90°
Formula units (Z)	4
Thermochemistry[8]
Heat capacity (C)	229.7 J/(K·mol)
Std molar entropy (S⦵298)	224.9 J·mol−1·K−1
Std enthalpy of formation (ΔfH⦵298)	125.5 kJ·mol−1
Enthalpy of fusion (ΔfH⦵fus)	17.36 kJ·mol−1
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	irritant
GHS labelling:[9]
Pictograms
Signal word	Warning
Hazard statements	H315, H319, H335, H410
Precautionary statements	P261, P264, P271, P273, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)	2 1 0
Flash point	non-flammable
Related compounds
Related PAHs	benzopyrene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Occurrence and properties

Pyrene was first isolated from coal tar, 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.^[11]

Reactions

Oxidation with chromate affords perinaphthenone and then naphthalene-1,4,5,8-tetracarboxylic acid. Pyrene undergoes a series of hydrogenation reactions and is susceptible to halogenation, Diels-Alder additions, and nitration, all with varying degrees of selectivity.^[11] Bromination occurs at one of the 3-positions.^[12]

Reduction with sodium affords the radical anion. From this anion, a variety of pi-arene complexes can be prepared.^[13]

Photophysics

Pyrene and its derivatives are used commercially to make dyes 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.^[14] The morphology of the signals change with the solvent. Its derivatives are also valuable molecular probes via fluorescence spectroscopy, having a high quantum yield and lifetime (0.65 and 410 nanoseconds, respectively, in ethanol at 293 K). Pyrene was the first molecule for which excimer behavior was discovered.^[15] Such excimer appears around 450 nm. Theodor Förster reported this in 1954.^[16]

Applications

STM image of self-assembled Br₄Py molecules on Au(111) surface (top) and its model (bottom; pink spheres are Br atoms).^[17]

Pyrene's fluorescence emission spectrum 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.

Diagram showing the numbering and ring fusion locations of pyrene according to IUPAC nomenclature of organic chemistry.

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.^[14]

Safety and environmental factors

Although it is not as problematic as benzopyrene, animal studies have shown pyrene is toxic to the kidneys and liver. It is now known that pyrene affects several living functions in fish and algae.^{[18][19][20][21]}

Its biodegradation has been heavily examined. The process commences with dihydroxylation at each of two kinds of CH=CH linkages.^[22] Experiments in pigs show that urinary 1-hydroxypyrene is a metabolite of pyrene, when given orally.^[23]

See also

• List of interstellar and circumstellar molecules
• Perhydropyrene