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Proton-Stabilized Photochemically Reversible E/ Z Isomerization of Spiropyrans.
L Kortekaas1, J Chen1, D Jacquemin2
1Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Mathematics and Natural Sciences , University of Groningen , Nijenborgh 4 , 9747AG Groningen , The Netherlands.
The Journal of Physical Chemistry. B
|May 31, 2018
Summary
Spiropyrans can be controllably opened to merocyanine forms using acid. This photochromic switching can be tuned for thermal stability and reversibility by careful acid selection.
Area of Science:
- Organic Chemistry
- Photochemistry
- Materials Science
Background:
- Spiropyrans are photochromic molecules known to undergo ring-opening reactions.
- Protonation and irradiation are key triggers for spiropyran transformation into merocyanine isomers.
- Understanding the conditions for controlled switching is crucial for developing advanced materials.
Purpose of the Study:
- To investigate the influence of acid concentration and strength on spiropyran ring-opening.
- To characterize the protonated Z-merocyanine isomer and its photochromic behavior.
- To explore pH-gated control over the thermal stability and reversibility of spiropyran photochromism.
Main Methods:
- Protonation of spiropyrans using acids of varying concentrations and strengths.
- Irradiation studies using UV and visible light to induce and control isomerization.
- Characterization of isomers using 1H NMR spectroscopy and UV/Vis spectroscopy.
Main Results:
- Acid concentration and strength precisely control the extent of spiropyran ring-opening.
- Strong acids induce spontaneous full ring opening to the Z-merocyanine isomer, which is characterizable.
- Reversible Z/E isomerization is achieved via light irradiation, with thermal stability observed under acidic conditions.
- A specific acid pKa range allows for thermally stable switching between spiropyran and E-merocyanine, enabling pH-gated photochromism.
Conclusions:
- The acid-induced ring-opening of spiropyrans is controllable by acid properties.
- Protonated merocyanine isomers exhibit distinct spectroscopic properties and photochromic behavior.
- Precise control over acid selection allows for tunable photochromic switching, opening avenues for advanced functional materials.
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