Editing Pyrene (section)

==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 (chemistry)|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.<ref name=Ullmann>Senkan, Selim and Castaldi, Marco (2003) "Combustion" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim.</ref>

===Reactions===
Oxidation with [[Chromate ion|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.<ref name=Ullmann/>  Bromination occurs at one of the 3-positions.<ref>{{cite journal | last1 = Gumprecht | first1 = W. H. | year = 1968 | title = 3-Bromopyrene | journal = Org. Synth. | volume = 48 | page = 30 | doi = 10.15227/orgsyn.048.0030 }}</ref>

Reduction with sodium affords the radical anion. From this anion, a variety of pi-arene complexes can be prepared.<ref>{{cite journal |doi=10.1107/S2053229614015290|title=Bis(pyrene)metal complexes of vanadium, niobium and titanium: Isolable homoleptic pyrene complexes of transition metals|year=2014|last1=Kucera|first1=Benjamin E.|last2=Jilek|first2=Robert E.|last3=Brennessel|first3=William W.|last4=Ellis|first4=John E.|journal=Acta Crystallographica Section C: Structural Chemistry|volume=70|issue=8|pages=749–753|pmid=25093352}}</ref>

===Photophysics===

Pyrene and its derivatives are used commercially to make [[dye]]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&nbsp;nm in DCM. The emission is close to the absorption, but moving at 375&nbsp;nm.<ref name=":0">{{Cite journal|last1=Tagmatarchis|first1=Nikos|last2=Ewels|first2=Christopher P.|last3=Bittencourt|first3=Carla|last4=Arenal|first4=Raul|last5=Pelaez-Fernandez|first5=Mario|last6=Sayed-Ahmad-Baraza|first6=Yuman|last7=Canton-Vitoria|first7=Ruben|date=2017-06-05|title=Functionalization of MoS 2 with 1,2-dithiolanes: toward donor-acceptor nanohybrids for energy conversion|journal=npj 2D Materials and Applications|language=en|volume=1|issue=1|pages=13|doi=10.1038/s41699-017-0012-8|issn=2397-7132|doi-access=free|hdl=10261/367520|hdl-access=free}}</ref>  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&nbsp;K).  Pyrene was the first molecule for which [[excimer]] behavior was discovered.<ref>{{cite journal |last1=Van Dyke |first1=David A. |last2=Pryor |first2=Brian A. |last3=Smith |first3=Philip G. |last4=Topp |first4=Michael R. |title=Nanosecond Time-Resolved Fluorescence Spectroscopy in the Physical Chemistry Laboratory: Formation of the Pyrene Excimer in Solution |journal=Journal of Chemical Education |date=May 1998 |volume=75 |issue=5 |pages=615 |doi=10.1021/ed075p615|bibcode=1998JChEd..75..615V }}</ref> Such excimer appears around 450&nbsp;nm.  [[Theodor Förster]] reported this in 1954.<ref>{{cite journal |last1=Förster |first1=Th. |last2=Kasper |first2=K. |title=Ein Konzentrationsumschlag der Fluoreszenz. |journal=Zeitschrift für Physikalische Chemie |date=June 1954 |volume=1 |issue=5_6 |pages=275–277 |doi=10.1524/zpch.1954.1.5_6.275}}</ref>