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]
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.
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]
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]
^Figueira-Duarte, Teresa M.; Müllen, Klaus (2011). "Pyrene-Based Materials for Organic Electronics". Chemical Reviews. 111 (11): 7260–7314. doi:10.1021/cr100428a. PMID21740071.
^ abSenkan, Selim and Castaldi, Marco (2003) "Combustion" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim.
^Kucera, Benjamin E.; Jilek, Robert E.; Brennessel, William W.; Ellis, John E. (2014). "Bis(pyrene)metal complexes of vanadium, niobium and titanium: Isolable homoleptic pyrene complexes of transition metals". Acta Crystallographica Section C: Structural Chemistry. 70 (8): 749–753. doi:10.1107/S2053229614015290. PMID25093352.
^Van Dyke, David A.; Pryor, Brian A.; Smith, Philip G.; Topp, Michael R. (May 1998). "Nanosecond Time-Resolved Fluorescence Spectroscopy in the Physical Chemistry Laboratory: Formation of the Pyrene Excimer in Solution". Journal of Chemical Education. 75 (5): 615. Bibcode:1998JChEd..75..615V. doi:10.1021/ed075p615.
^Förster, Th.; Kasper, K. (June 1954). "Ein Konzentrationsumschlag der Fluoreszenz". Zeitschrift für Physikalische Chemie. 1 (5_6): 275–277. doi:10.1524/zpch.1954.1.5_6.275.
^Oliveira, M.; Ribeiro, A.; Hylland, K.; Guilhermino, L. (2013). "Single and combined effects of microplastics and pyrene on juveniles (0+ group) of the common goby Pomatoschistus microps (Teleostei, Gobiidae)". Ecological Indicators. 34: 641–647. doi:10.1016/j.ecolind.2013.06.019.
^Oliveira, M.; Gravato, C.; Guilhermino, L. (2012). "Acute toxic effects of pyrene on Pomatoschistus microps (Teleostei, Gobiidae): Mortality, biomarkers and swimming performance". Ecological Indicators. 19: 206–214. doi:10.1016/j.ecolind.2011.08.006.
^Oliveira, M.; Ribeiro, A.; Guilhermino, L. (2012). "Effects of exposure to microplastics and PAHs on microalgae Rhodomonas baltica and Tetraselmis chuii". Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 163: S19–S20. doi:10.1016/j.cbpa.2012.05.062.
^Oliveira, M.; Ribeiro, A.; Guilhermino, L. (2012). "Effects of short-term exposure to microplastics and pyrene on Pomatoschistus microps (Teleostei, Gobiidae)". Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 163: S20. doi:10.1016/j.cbpa.2012.05.063.
^Keimig, S. D.; Kirby, K. W.; Morgan, D. P.; Keiser, J. E.; Hubert, T. D. (1983). "Identification of 1-hydroxypyrene as a major metabolite of pyrene in pig urine". Xenobiotica. 13 (7): 415–20. doi:10.3109/00498258309052279. PMID6659544.