High-pressure sapphire capillary cell for synchrotron single-crystal X-ray diffraction measurements to 1500 bar

A new sapphire capillary pressure cell for single-crystal X-ray diffraction measurements at moderate pressures (200−1500 bar; 1 bar = 100 kPa) has been developed and optimized for use on beamline I19 at Diamond Light Source. The three-component cell permits optical centring of the crystal and in situ pressure modification to a precision of 1 bar. Compression of hexamethylenetetramine and its deuterated analogue to 1000 bar was performed, showcasing the accuracy and precision of the measurements, and highlighting evidence of a geometric isotope effect.

A multi-state fluorescent switch based on a diarylethene with an acridine unit

A new asymmetrical fluorescent diarylethene derivative with an acridine unit was synthesized by Schiff base condensation. The derivative was sensitive to lights and special metal ions. Stimulated by UV/vis lights and Zn²⁺, distinct changes were observed in UV-vis and fluorescent spectra. Upon addition of Zn²⁺, the derivative emission peak was blue-shifted by 34nm and the emission intensity was enhanced by 16 fold, accompanied by the fluorescent color changed from red to light yellow, due to the formation of a 1:1 metal/ligand complex. The complex exhibited excellent fluorescence switching upon irradiation with UV light. Taking advantage of the lights and Zn²⁺ stimuli (inputs), and fluorescence intensity at 580nm (output), a molecular logic gate was constructed. Moreover, a new absorption band centered at 420-450nm emerged upon exposure to Zn²⁺. The dramatic color change of the solution made the 'naked-eyes' detection of Zn²⁺ possible.

Piezochromism and hydrochromism through electron transfer: new stories for viologen materials

A pyridinium-carboxylate compound undergoes reversible color change under pressure owing to the formation of radicals via electron transfer; dehydration and hydration can also trigger electron transfer.

While viologen derivatives have long been known for electrochromism and photochromism, here we demonstrated that a viologen-carboxylate zwitterionic molecule in the crystalline state exhibits piezochromic and hydrochromic behaviors. The yellow crystal undergoes a reversible color change to red under high pressure, to green after decompression, and finally back to yellow upon standing at ambient pressure. Ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance X-ray diffraction and DFT calculations suggested that the piezochromism is due to the formation of radicals via pressure-induced electron transfer from carboxylate to pyridinium, without a crystallographic phase transition. It was proposed that electron transfer is induced by pressure-forced reduction of intermolecular donor–acceptor contacts. The electron transfer can also be induced by dehydration, which gives a stable green anhydrous radical phase. The color change is reversible upon reabsorption of water, which triggers reverse electron transfer. The compound not only demonstrates new chromic phenomena for viologen compounds, but also represents the first example of organic mechanochromism and hydrochromism associated with radical formation via electron transfer.

Shear-Triggered Crystallization and Light Emission of a Thermally Stable Organic Supercooled Liquid

Thermodynamics drive crystalline organic molecules to be crystallized at temperatures below their melting point. Even though molecules can form supercooled liquids by rapid cooling, crystalline organic materials readily undergo a phase transformation to an energetically favorable crystalline phase upon subsequent heat treatment. Opposite to this general observation, here, we report molecular design of thermally stable supercooled liquid of diketopyrrolopyrrole (DPP) derivatives and their intriguing shear-triggered crystallization with dramatic optical property changes. Molten DPP8, one of the DPP derivatives, remains as stable supercooled liquid without crystallization through subsequent thermal cycles. More interestingly, under shear conditions, this supercooled liquid DPP8 transforms to its crystal phase accompanied by a 25-fold increase in photoluminescence (PL) quantum efficiency and a color change. By systematic investigation on supercooled liquid formation of crystalline DPP derivatives and their correlation with chemical structures, we reveal that the origin of this thermally stable supercooled liquid is a subtle force balance between aromatic interactions among the core units and van der Waals interactions among the aliphatic side chains acting in opposite directions. Moreover, by applying shear force to a supercooled liquid DPP8 film at different temperatures, we demonstrated direct writing of fluorescent patterns and propagating fluorescence amplification, respectively. Shear-triggered crystallization of DPP8 is further achieved even by living cell attachment and spreading, demonstrating the high sensitivity of the shear-triggered crystallization which is about 6 orders of magnitude more sensitive than typical mechanochromism observed in organic materials.

Reversible piezochromism in a molecular wine-rack

Coupling of a ‘wine-rack’ lattice motif with molecular flexibility leads to a large piezochromic response in an organic material.

processPIXEL: a program to generate energy-vector models from Gavezzotti'sPIXELcalculations

A command-line program is presented to convert the output from Gavezzotti'sPIXELcalculations to Shishkin's energy-vector models representing the intermolecular interaction topology. The output models comprise sets of vectors joining the centres of the molecules in a crystal structure, scaled so that the vector representing the most stabilizing pairwise interaction has length equal to half of the corresponding intermolecular separation. When the energy-vector model is packed, the most stabilizing pairwise interaction is represented as a continuous line between interacting molecules, while the other intermolecular interactions are shown as discontinuous lines, with a smaller gap representing a more stabilizing interaction. The energy-vector models can be overlaid on the crystal structure using theMercuryvisualizer to enable convenient visualization of structural motifs that contribute significantly to the overall crystal packing energy.