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

DOI: 10.1039/C3CE41933A DOI Help

Authors: Christopher Woodall (University of Bath) , Simon Brayshaw (University of Bath) , Stefanie Schiffers (University of Bath) , Dave Allan (Diamond Light Source) , Simon Parsons (The University of Edinburgh) , Rafael Valiente (University of Cantabria) , Paul R. Raithby (University of Bath)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: CrystEngComm , VOL 16 (11) , PAGES 2119 - 2128

State: Published (Approved)
Published: November 2013

Open Access Open Access

Abstract: 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 P21/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 thiophenethiophene interaction at 4.45 GPa to a benzothiophenebenzothiophene 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 ð–ð* absorption band and a colour change in the crystal from colourless to red with increasing pressure.

Subject Areas: Engineering

Instruments: I19-Small Molecule Single Crystal Diffraction