Issue 38, 2021

Direct evidence for distinct colour origins in ROY polymorphs

Abstract

ROY is one of the most well-studied families of crystal structures owing to it being the most polymorphic organic material on record. The various red, orange, and yellow colours of its crystal structures are widely-believed to originate from molecular conformation, though the orange needle (ON) polymorph is thought to be an exception. We report high-pressure, single-crystal X-ray measurements which provide direct experimental evidence that the colour origin in ON is intermolecular, revealing that the molecule undergoes minimal deformation but still exhibits a pronounced, reversible, pale orange → dark red colour change between ambient pressure and 4.18 GPa. Our experimental data are rationalised with band structures, calculated using an accurate hybrid DFT approach, where we are able to account for the variation in colour for five polymorphs of ROY. We highlight the outlier behaviour of ON which shows marked π⋯π stacking interactions that are directly modified through application of pressure. Band structure calculations confirm these intermolecular interactions as the origin of the colour change.

Graphical abstract: Direct evidence for distinct colour origins in ROY polymorphs

Supplementary files

Article information

Article type
Edge Article
Submitted
23 Jul 2021
Accepted
27 Aug 2021
First published
01 Sep 2021
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2021,12, 12711-12718

Direct evidence for distinct colour origins in ROY polymorphs

L. R. Warren, E. McGowan, M. Renton, C. A. Morrison and N. P. Funnell, Chem. Sci., 2021, 12, 12711 DOI: 10.1039/D1SC04051K

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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