Abstract
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.
Highlights
Spiropyran and spirooxazine are photochromically active compounds
We identified five novel crystal structures
A closer look at the structural features shows a high similarity between the different compounds
Summary
Spiropyran and spirooxazine are photochromically active compounds. Their photochromic character stems from a ring-opening isomerization by breaking the Cspiro -O bond upon UV-light absorption [1]. The limited solid-state response of the compounds is expected to be due to the large structural changes accompanying the ring opening mechanism In principle, this issue can be tackled using the so-called chemical modification method, in which the spiro compound is given functional groups large enough to open up the crystal structure, allowing the compound to become photochromically active at the solid state. This issue can be tackled using the so-called chemical modification method, in which the spiro compound is given functional groups large enough to open up the crystal structure, allowing the compound to become photochromically active at the solid state This approach, turned out to be challenging [2].
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