Reversible piezochromism in a molecular wine-rackElectronic supplementary information (ESI) available: CIFs of high-pressure structures, atomistic compression movie (QuickTime format), experimental details for high-pressure X-ray diffraction and UV-Vis absorption spectra measurements, photographs of ROY crystals, Gaussian fits to absorption spectra first derivatives, structure of the Y polymorph at 30 K and analysis of intermolecular interactions. CCDC 1058322-1058332. For ESI and crystallograph

• Main Authors: Harty, Elena L, Ha, Alex R, Warren, Mark R, Thompson, Amber L, Allan, David R, Goodwin, Andrew L, Funnell, Nicholas P
• Format: Article
• Language: English
• ISSN: 1359-7345; 1364-548X
• DOI: 10.1039/c5cc02916c

The highly-polymorphic, strongly-coloured 'ROY' system exhibits a yellow → orange → red piezochromic response under hydrostatic compression. The 'Y' (yellow) polymorph accommodates the effect of pressure via a wine-rack-type mechanism, made accessible by the conformational flexibility of the molecule, while retaining the crystal symmetry of the parent Y form. Decompression from 1.49 GPa demonstrates reversibility of this behaviour. Coupling of a 'wine-rack' lattice motif with molecular flexibility leads to a large piezochromic response in an organic material.