A structural analysis of spiropyran and spirooxazine compounds and their polymorphs

Vanessa Kristina Seiler, Nikolay Tumanov, Koen Robeyns, Johan Wouters, Benoit Champagne, Tom Leyssens

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In this work, crystal structures of commercially available photochromic compounds, i.e., spiropyrans and spirooxazines, were investigated by single-crystal X-ray diffraction. A total of five new structures were obtained via isothermal evaporation experiments under different conditions, namely 1,3,3-Trimethylindolino-benzopyrylospiran (I), 1,3,3-Trimethylindolinonaphtospirooxaxine (II), 1-(2-Hydroxyethyl)-3,3-dimethylindolino-6′-nitrobenzopyrylospiran (III), and 1,3,3-Trimethylindolino-8′-methoxybenzopyrylospiran (IVa and IVb). Since the basic structure of a spiropyran/-oxazine does not present typical hydrogen bond accepting and donating groups, this study illustrates the importance of additional functional groups connected to this kind of molecules to induce specific intermolecular interactions. Our results show that possible hydrogen bonding interactions are rather weak due to the high steric demand of these compounds. These results are supported by a search of the Cambridge structural database focused on related structures.

Original languageEnglish
Article number84
Issue number3
Publication statusPublished - 13 Mar 2017


  • Crystal engineering
  • Crystal structure
  • Photochromic compounds
  • Spirooxazine
  • Spiropyran


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