4.6 Article

Unexpected Acid-Triggered Formation of Reversibly Photoswitchable Stenhouse Salts from Donor-Acceptor Stenhouse Adducts

Journal

CHEMISTRY-A EUROPEAN JOURNAL
Volume 28, Issue 28, Pages -

Publisher

WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.202200497

Keywords

donor-acceptor Stenhouse adducts; photochromism; reversibly photoswitchable dyes; Stenhouse salts

Funding

  1. European Union Horizon 2020 research and innovation program MSCA-IF grant (SmartSAST grant) [890479]
  2. Marie Curie Actions (MSCA) [890479] Funding Source: Marie Curie Actions (MSCA)

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Water-soluble DASAs based on indoline as donor and methyl or trifluoromethyl pyrazolone-based acceptors were developed, and the reversible photoswitching mechanism was confirmed through photophysical analysis and photochemical studies. The formation of StS was observed under acidic conditions.
Donor-acceptor Stenhouse adducts (DASAs) are reversibly photoswitchable dyes, which are able to interconvert between a red/NIR absorbing triene-like state and a colorless cyclic state. Although optically attractive for multiple applications, their low solubility and lack of photoswitching in water impede their use in aqueous environments. We developed water-soluble DASAs based on indoline as donor and methyl, or trifluoromethyl, pyrazolone-based acceptors. In acetonitrile, photophysical analysis and photochemical studies, accounted with a three-state kinetic model, confirmed the reversible photoswitching mechanism previously proposed. In water, the colorless cyclic state is a thermodynamic sink at neutral pH values. In contrast, in acidic conditions, we observed a fast scrambling of DASAs' end-group resulting in the in situ formation of Stenhouse salts (StS), which are in turn capable of reversible photoswitching. We believe that this unexpected result is of interest not only for the future design of DASAs with improved stability, but also for further development and applications of StS as photoswitchable probes.

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