Editing Photoisomerization (section)

==Examples==
Azobenzenes,<ref name=azo>{{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}}</ref> [[stilbene]]s,<ref>{{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.}}</ref> [[spiropyran]]s,<ref>{{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}}</ref> are prominent classes of compounds subject to photoisomerism.

:[[File:Synthesis of quadricyclane from norbornadiene.png|400px|center|thumb|Photoisomerization of norbornadiene to quadricyclane.]]
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]] ([[photoswitch]]s).<ref>{{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 }}</ref>

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 [[chemical bond|bond]], and rotation or inversion around the double bond affords isomerization between the two states.<ref>{{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 }}</ref> 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]].