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Photoisomerization of azobenzene

In chemistry, photoisomerization is a molecular behavior in which structural change between isomers is caused by photoexcitation.[1] Both reversible and irreversible isomerization reactions exist. However, the word "photoisomerization" usually indicates a reversible process.


Photoisomerizable molecules are already put to practical use, for instance, in pigments for rewritable CDs, DVDs, and 3D optical data storage solutions. In fact, photoisomerization of the molecule retinal in the eye is the mechanism that allows for vision. In addition, recent interest in photoisomerizable molecules has been aimed at molecular devices, such as molecular switches,[2][3] molecular motors,[4] 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.[5] Due to the photoisomerization is possible to induce a molecular reorintation in the liquid crystal bulk, which is used in holography,[6] as spatial filter[7] or optical switching.[8]

Methyl red molecule. A common azo-dye used in liquid crystal doping.


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.[9] 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-pi-methane rearrangement.

See alsoEdit


  1. ^ "Photoisomerization". IUPAC Compendium of Chemical Terminology. 2009. doi:10.1351/goldbook.P04622. ISBN 978-0-9678550-9-7.
  2. ^ Mammana, A.; et al. (2011). "A Chiroptical Photoswitchable DNA Complex" (PDF). Journal of Physical Chemistry B. 115 (40): 11581–11587. doi:10.1021/jp205893y. PMID 21879715.
  3. ^ Mokdad, A; Belof, J; Yi, S; Shuler, S; McLaughlin, M; Space, B; Larsen, R (2008). "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 of Physical Chemistry B. 112 (36): 8310–8315. Bibcode:2008JPCA..112.8310M. doi:10.1021/jp803268r. PMID 18700732.
  4. ^ Vachon, J.; et al. (2014). "An ultrafast surface-bound photo-active molecular motor". Photochemical and Photobiological Sciences. 13 (2): 241–246. doi:10.1039/C3PP50208B. PMID 24096390.
  5. ^ Janossy, I.; Szabados, L. (1 October 1998). "Optical reorientation of nematic liquid crystals in the presence of photoisomerization". Physical Review E. 58 (4): 4598. Bibcode:1998PhRvE..58.4598J. doi:10.1103/PhysRevE.58.4598.
  6. ^ Chen, Alan G; Brady, David J (1992). "Real-time holography in azo-dye-doped liquid crystals". Optics Letters. 17 (6): 441. Bibcode:1992OptL...17..441C. doi:10.1364/OL.17.000441.
  7. ^ Kato, Jun-ichi; Yamaguchi, Ichirou (1996). "Nonlinear spatial filtering with a dye-doped liquid-crystal cell". Optics Letters. 21 (11): 767–769. Bibcode:1996OptL...21..767K. doi:10.1364/OL.21.000767.
  8. ^ Maly, Kenneth E; Wand, Michael D (2002). "Bistable ferroelectric liquid crystal photoswitch triggered by a dithienylethene dopant". Journal of the American Chemical Society. 124 (27): 7898–7899. doi:10.1364/OPEX.13.002358. PMID 19495125.
  9. ^ "Spectroscopic and computational studies of the photoisomerization". Journal of Molecular Structure. 1178: 538–543. doi:10.1016/j.molstruc.2018.10.071.