|Systematic IUPAC name
3D model (JSmol)
|Molar mass||322.35782 g/mol|
|Melting point||179-180 °C (354-356 F)|
|Boiling point||476.32 °C at 760 mmHg|
|Water Solubility at 25 deg C (mg/L): 0.0129; Wat Sol (v1.01 est) = 0.046355 mg/L|
|Main hazards||Skin, respiratory, and serious eye irritation|
|Flash point||241.87 °C|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Spiropyran is an organic compound with the chemical formula C19H18N2O3. Its systematic name is 1',3',3'-trimethyl-6-nitroindolene-2-spiro-2-benzopyran. A molecule of spiropyran consists of a molecule of bicyclic indole ring jointed at C-2 atom with a molecule of bicyclic benzopyran ring (also called chromene), forming a spiro compound. 1 and 2 methyl groups (-CH3) are attached to N-1 and C-3 atom of the indole ring respectively. Another molecule of nitro functional group is attached to C-5 atom of the benzopyran ring. The C_spiro-O bond is susceptible to external mechanical and photochemical energy. The cleavage of this bond would undergo a 6-pi electrocyclic ring opening (ERO) reaction, producing zwitterionic merocyanine.
Spiropyran is a solid that exhibits different physical properties under discrete mechanical and/or photoisomeric states. It has a melting point range of 179-180 °C (354-356 F), and its boiling point is 76.32 °C (at 760 mmHg). Spiropyran is insoluble in water.
Spiropyran is one of the oldest families of photochromes. The photochromic reactions of spiropyrans were first discovered by Fisher and Hirshberg in 1952, and Hirshberg subsequently proposed the idea of using the phenomenon for a "photochemical erasable memory"  In the course of time, spiropyrans have become on of the most extensively studied groups of photochemical compounds because of their potential applications based on reversible color and other changes in physical and chemical properties. Recent research has suggested that photochromic spiropyran could be applied in self-developing photography, actinometry, displays, filters, and lenses of variable optical density, including eye-protective glasses and other molecular devices .
Spiropyran is generally produced by condensation of methylene bases with o-hydroxy aromatic aldehydes. The general reaction step is shown in Figure 2.
Beta-elimination produces a double bond at nitrogen and C-2 carbon.
AdN: The lone pair on carbon attacks the electrophilic carbon of the carbonyl on o-hydroxy aromatic aldehydes, joining the two molecules together.
An intramolecular proton transfer.
AdN: The lone pair on oxygen attacks C-2 carbon, joining the oxygen atom and C-2 carbon. This step creates a spiro compound.
E2 elimination creates a double bond and releases a molecule of water.
 Spiropyran can undergo a reversible pericyclic reaction that produces zwitterionic merocyanine. Upon application of mechanical stress and/ or light, the bond between the spiro carbon and oxygen breaks and undergoes a 6-pi electrocyclic ring opening reaction via pi->sigma* pi type interaction. The reaction summarized in Figure 1 depicts the reaction mechanism with the application of force. Long strings of polymers are added to C-5', N-1', and C-8 of spiropyran molecule to apply forces that could weaken the C_spiro-O bond. After the cleavage of the bond, the spiro carbon achieves sp² hybridization and becomes planar, the aromatic group rotates, aligns its π-orbitals with the rest of the molecule, and a conjugated system forms with ability to absorb photons of visible light, and therefore the product, an E, E-isomer of merocyanine, appear colorful. 
Recent research has suggested that photochromic spiropyran could be applied in self-developing photography, actinometry, displays, filters, and lenses of variable optical density, including eye-protective glasses and other molecular devices.
Spiropyran is an irritant which can cause skin, respiratory, and serious eye irritation upon exposure. When combusted, spiropyran decomposes into hazardous products: carbon oxides and nitrogen oxides. For storage, spiropyran should be kept in container tightly closed in a dry and well-ventilated place.
- Fischer, E.; Hirshberg, Y. J . Ch. Soc. W2, 4522.doi:10.1039/JR9520004518
- Hirshberg, Y. J. Am. Ch. Soc. 1956, 78, 2304.
- Pang, M.; Nie, Y.; Wang, Y.; Meng, J.; Wang, J. Synthesis of New Spiropyrans With a Polyaromatic or Heteroaromatic Pendant and Their Photochromic Behaviors. Chinese Journal of Chemistry. [Online] 2010, 20, 1102-1108. http://onlinelibrary.wiley.com/doi/10.1002/cjoc.20020201032/pdf
- Lukyanov, B. S.; Lukyanova, M. B. Spiropyrans: Synthesis, Properties, and Application. (Review). CHEMISTRY OF HETEROCYCLIC COMPOUNDS. [Online] 2005, 41(3), 281-311. http://www.springerlink.com/content/g793l1j87hn73g88/
- Aldoshin, S. M. Spiropyrans: structural features and photochemical properties. Russ. Chem. Rev. [Online] 1990, 59, 663. http://iopscience.iop.org/0036-021X/59/7/R06/pdf/RCR_59_7_R06.pdf
- Davis, D. A.; Hamilton, A.; Yang, J.; Cremar, L. D.; Van Gough, D.; Potisek, S. L.; Ong, M. T.; Braun, P. V.; Martínez, T. J.; White, S. R.; Moore, J. S.; Sottos, N. R. Force-induced activation of covalent bonds in mechanoresponsive polymeric materials. Nature. [Online] 2009, 459, 68-72. http://www.ncbi.nlm.nih.gov/pubmed/19424152
- Moore, J. S. (2012, September). Other Pericyclic Reactions in Chemistry 332. University of Illinois at Urbana-Champaign.