High-pressure crystallographic and spectroscopic studies on two molecular dithienylethene switches

Christopher H. Woodall, Simon K. Brayshaw, Stefanie Schiffers, David R. Allan, Simon Parsons, Rafael Valiente, Paul R. Raithby

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Single crystals of the dithienylethene compounds, 1,2-bis(2- methylbenzothiophen-3-yl)perfluorocyclopentene 1 and 1,2-bis(2,5- dimethylthiophen-3-yl)perfluorocyclopentene 2 undergo pressure-induced single-crystal to single-crystal phase transitions between 4.45-5.35 GPa and 4.15-5.70 GPa, respectively. For 1, there is a smooth reduction in unit-cell volume of ~20% from ambient pressure to 4.45 GPa, followed by a dramatic reduction in volume that coincides with a 7.7% increase in the b axis length. Above the pressure of 5.38 GPa a smooth volume reduction continues. In contrast, for 2, there is a continuous change in unit-cell volume with an observed space group change from C2/c to P2/c, between the pressures of 4.15 and 5.70 GPa. In the crystals of 1 between 4.45 and 5.38 GPa adjacent molecules slide over each other and the dominant stacking interaction changes from a thiophene⋯thiophene interaction at 4.45 GPa to a benzothiophene⋯ benzothiophene interaction at 5.38 GPa and, within each molecule, the benzothiophene groups show a significant reorientation at the phase transition. In 2 there is a loss of molecular symmetry, concomitant with the change in space group, at the phase transition with the asymmetric unit changing from containing half a unique molecule to two independent molecules. The molecules show significant reorientations of their ring systems. The nature of the observed transition in 1 was investigated using solid-state computational methods to prove the superior thermodynamic stability of the high-pressure phase to the lower pressure phase at pressures above 5.38 GPa. Solid state UV-Vis spectroscopy of 1, over the pressure range from ambient to 15.4 GPa showed that the compound displayed piezochromism with a significant red shift in the π-π* absorption band and a colour change in the crystal from colourless to red with increasing pressure.
Original languageEnglish
Pages (from-to)2119-2128
Number of pages10
Issue number11
Early online date15 Nov 2013
Publication statusPublished - 21 Mar 2014


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