A mechanophysical phase transition provides a dramatic example of colour polymorphism: the tribochromism of a substituted trimethylenetetrahydrofuran-2-oneReport as inadecuate

A mechanophysical phase transition provides a dramatic example of colour polymorphism: the tribochromism of a substituted trimethylenetetrahydrofuran-2-one - Download this document for free, or read online. Document in PDF available to download.

Chemistry Central Journal

, 8:70

Current Topics in Chemical CrystallographyAnalytical Chemistry


BackgroundDerivatives of fulgides have been shown to have interesting photochromic properties. We have synthesised a number of such derivatives and have found, in some cases, that crystals can be made to change colour on crushing, a phenomenon we have termed -tribochromism-. We have studied a number of derivatives by X-ray crystallography, to see if the colour is linked to molecular structure or crystal packing, or both, and our structural results have been supported by calculation of molecular and lattice energies.

ResultsA number of 5-dicyanomethylene-4-diphenylmethylene-3-disubstitutedmethylene-tetrahydrofuran-2-one compounds have been prepared and structurally characterised. The compounds are obtained as yellow or dark red crystals, or, in one case, both. In two cases where yellow crystals were obtained, we found that crushing the crystals gave a deep red powder. Structure determinations, including those of the one compound which gave both coloured forms, depending on crystallisation conditions, showed that the yellow crystals contained molecules in which the structure comprised a folded conformation at the diphenylmethylene site, whilst the red crystals contained molecules in a twisted conformation at this site. Lattice energy and molecular conformation energies were calculated for all molecules, and showed that the conformational energy of the molecule in structure IIIa yellow is marginally higher, and the conformation thus less stable, than that of the molecule in structure IIIb red. However, the van der Waals energy for crystal structure IIIa , is slightly stronger than that of structure IIIb – which may be viewed as a hint of a metastable packing preference for IIIa , overcome by the contribution of a more stabilising Coulomb energy to the overall more favourable lattice energy of structure IIIb .

ConclusionsOur studies have shown that the crystal colour is correlated with one of two molecular conformations which are different in energy, but that the less stable conformation can be stabilised by its host crystal lattice.

Open image in new windowGraphical abstractGraphical representation of the structural and colour change in the tribochromic compound III.

KeywordsPhotochromism Tribochromism Crystal structure analysis Molecular and lattice energy calculations Colour polymorphism Electronic supplementary materialThe online version of this article doi:10.1186-s13065-014-0070-3 contains supplementary material, which is available to authorized users.

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