photoisomerization
{{Short description|Chemical change induced by light}}
{{Use American English|date = April 2019}}
File:AzobenzeneIsom,no Engl.png
In chemistry, photoisomerization is a form of isomerization induced by photoexcitation.{{cite book|chapter=Photoisomerization|year=2009|doi=10.1351/goldbook.P04622|title=IUPAC Compendium of Chemical Terminology|isbn=978-0-9678550-9-7}} Both reversible and irreversible photoisomerizations are known for photoswitchable compounds. The term "photoisomerization" usually, however, refers to a reversible process.
Applications
Photoisomerization of the compound retinal in the eye allows for vision.
Photoisomerizable substrates have been put to practical use, for instance, in pigments for rewritable CDs, DVDs, and 3D optical data storage solutions. In addition, interest in photoisomerizable molecules has been aimed at molecular devices, such as molecular switches,{{Cite journal |last1=Mammana |first1=A. |year=2011 |title=A Chiroptical Photoswitchable DNA Complex |journal=Journal of Physical Chemistry B |volume=115 |issue=40 |pages=11581–11587 |doi=10.1021/jp205893y |pmid=21879715 |display-authors=etal|url=https://pure.rug.nl/ws/files/10462706/2011JPhysChemBMammanaSupp.pdf |hdl=11370/cca715c8-861f-4500-943f-028c95e8e55e |s2cid=33375716 |hdl-access=free }}{{cite journal | last1=Mokdad | first1 = A | last2 = Belof | first2 = J | last3 = Yi | first3 = S | last4 = Shuler | first4 = S | last5 = McLaughlin | first5 = M | last6 = Space | first6 = B | last7 = Larsen | first7 = R | title = Photophysical Studies of the Trans to Cis Isomerization of the Push−Pull Molecule: 1-(Pyridin-4-yl)-2-(N-methylpyrrol-2-yl)ethene (mepepy) | journal=Journal of Physical Chemistry B | volume = 112 | issue = 36 | pages = 8310–8315 | year = 2008 | doi = 10.1021/jp803268r | pmid = 18700732 | bibcode = 2008JPCA..112.8310M }} molecular motors,{{Cite journal |last1=Vachon |first1=J. |year=2014 |title=An ultrafast surface-bound photo-active molecular motor |journal=Photochemical and Photobiological Sciences |volume=13 |issue=2 |pages=241–246 |doi=10.1039/C3PP50208B |pmid=24096390 |s2cid=23165784 |display-authors=etal|url=http://dare.uva.nl/personal/pure/en/publications/an-ultrafast-surfacebound-photoactive-molecular-motor(ca92afa2-9b98-44e8-b06c-c29c41da008d).html }} and molecular electronics.
Another class of device that uses the photoisomerization process is as an additive in liquid crystals to change their linear and nonlinear properties.{{cite journal |last1=Janossy |first1=I. |last2=Szabados |first2=L. |title=Optical reorientation of nematic liquid crystals in the presence of photoisomerization |journal=Physical Review E |date=1 October 1998 |volume=58 |issue=4 |page=4598 |doi=10.1103/PhysRevE.58.4598|bibcode=1998PhRvE..58.4598J |s2cid=26508261 }} Due to the photoisomerization is possible to induce a molecular reorientation in the liquid crystal bulk, which is used in holography,{{cite journal |last1=Chen |first1=Alan G |last2=Brady |first2=David J |title=Real-time holography in azo-dye-doped liquid crystals |journal=Optics Letters |date=1992 |volume=17 |issue=6 |pages=441–3 |doi=10.1364/OL.17.000441|pmid=19784354 |bibcode=1992OptL...17..441C |s2cid=20923350 }} as spatial filter{{cite journal |last1=Kato |first1=Jun-ichi |last2=Yamaguchi |first2=Ichirou |title=Nonlinear spatial filtering with a dye-doped liquid-crystal cell |journal=Optics Letters |date=1996 |volume=21 |issue=11 |pages=767–769 |doi=10.1364/OL.21.000767|pmid=19876152 |bibcode=1996OptL...21..767K }} or optical switching.{{cite journal |last1=Maly |first1=Kenneth E |last2=Wand |first2=Michael D |title=Bistable ferroelectric liquid crystal photoswitch triggered by a dithienylethene dopant |journal=Journal of the American Chemical Society |date=2002 |volume=124 |issue=27 |pages=7898–7899 |doi=10.1364/OPEX.13.002358|pmid=19495125 |doi-access=free}}
Examples
Azobenzenes,{{cite journal|doi=10.1021/cr970155y|pmid=12428986|title=Photoinduced Motions in Azo-Containing Polymers|journal=Chemical Reviews|volume=102|issue=11|pages=4139–4176|year=2002|last1=Natansohn|first1=Almeria|last2=Rochon|first2=Paul}} stilbenes,{{cite journal|doi=10.1021/cr00003a007|title=Photoisomerization dynamics of stilbenes|journal=Chemical Reviews|volume=91|issue=3|pages=415–436|year=1991|last1=Waldeck|first1=David H.}} spiropyrans,{{cite journal|doi=10.1039/C3CS60181A|pmid=23979515|title=Spiropyran-based dynamic materials|journal=Chem. Soc. Rev.|volume=43|issue=1|pages=148–184|year=2014|last1=Klajn|first1=Rafal|doi-access=free}} are prominent classes of compounds subject to photoisomerism.
:File:Synthesis of quadricyclane from norbornadiene.png
In the presence of a catalyst, norbornadiene converts to quadricyclane via ~300nm UV radiation. When converted back to norbornadiene, quadryicyclane’s ring strain energy is liberated in the form of heat (ΔH = −89 kJ/mol). This reaction has been proposed to store solar energy (photoswitchs).{{cite journal|doi=10.1070/RC2002v071n11ABEH000745|title=Norbornadiene–quadricyclane as an abiotic system for the storage of solar energy|journal=Russian Chemical Reviews|volume=71|issue=11|pages=917–927|year=2002|last1=Dubonosov|first1=Alexander D.|last2=Bren|first2=Vladimir A.|last3=Chernoivanov|first3=V. A.|bibcode=2002RuCRv..71..917D|s2cid=250890545 }}
Photoisomerization behavior can be roughly categorized into several classes. Two major classes are trans–cis (or E–Z) conversion, and open-closed ring transition. Examples of the former include stilbene and azobenzene. This type of compounds has a double bond, and rotation or inversion around the double bond affords isomerization between the two states.{{Cite journal|title=Spectroscopic and computational studies of the photoisomerization|journal=Journal of Molecular Structure|volume=1178|pages=538–543|doi=10.1016/j.molstruc.2018.10.071|bibcode=2019JMoSt1178..538K|year=2019 | last1 = Kazem-Rostami | first1 = Masoud | last2 = Akhmedov | first2 = Novruz G. | last3 = Faramarzi | first3 = Sadegh|s2cid=105312344 }} Examples of the latter include fulgide and diarylethene. This type of compounds undergoes bond cleavage and bond creation upon irradiation with particular wavelengths of light. Still another class is the di-π-methane rearrangement.
Coordination chemistry
Many complexes are often photosensitive and many of these complexes undergo photoisomerization.{{cite book|
title=Photochemistry and Photophysics of Metal Complexes|author=D. M. Roundhill|publisher=Springer|year=1994|isbn= 978-1-4899-1495-8}} One case is the conversion of the colorless cis-bis(triphenylphosphine)platinum chloride to the yellow trans isomer.
Some coordination complexes undergo change in their spin state upon illumination, i.e. these are photosensitive spin crossover complexes.{{cite journal|doi=10.1016/S0010-8545(01)00381-2|title=Photoswitchable coordination compounds|journal=Coordination Chemistry Reviews|volume=219–221|pages=839–879|year=2001|last1=Gã¼Tlich|first1=P.}}
See also
References
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