(9-Isocyanoanthracene)gold(I) Complexes Exhibiting Two Modes of Crystal Jumps by Different Structure Change Mechanisms

Fluorene-containing binuclear gold(I) complexes: High-contrast mechanochromic fluorescence quenching and information encryption application

A series of fluorene-based binuclear gold(I) complexes I-VI have been successfully synthesized. Their structures were characterized by nuclear magnetic resonance, high-resolution mass spectrometry, and single crystal X-ray diffraction techniques. The fluorescence switching characteristics of complexes I-VI in the solid state were studied by photoluminescence spectroscopy. Luminogens I-VI showed different solid-state fluorescence involving blue-green, yellow-green and yellow colors before mechanical stimulation, which suggests that the solid fluorescent properties of I-VI can be effectively manipulated by positional isomerism and increasing conjugation strategies. Interestingly, their solid fluorescence intensities of all luminogens weakened significantly upon grinding. Impressively, luminogen IV barely displayed macroscopic fluorescence after grinding, indicative of its remarkable high-contrast mechanochromic fluorescence quenching feature. The unique mechanofluorochromic phenomena of I-VI were fully elucidated by analyzing X-ray diffraction patterns changes of I-VI before and after grinding and crystal packing structure of III. Furthermore, an effective dual information encryption system was constructed based on complex IV.

Ferroelastic ionic organic crystals that self-heal to 95

The realm of self-healing materials integrates chemical and physical mechanisms that prevent wear and fracturing and extend the operational lifetime. Unlike the favorable rheology of amorphous soft materials that facilitates efficient contact between fragments, the efficiency of recovery of atomistically ordered materials is restricted by slower interfacial mass transport and the need for ideal physical alignment, which limits their real-world application. We report drastic enhancements in efficiency and recovery time in the self-healing of anilinium bromide, challenging these limitations. Crystals of this material recovered up to 49% within seconds and up to 95% after 100 min via ferroelastic detwinning. The spatial evolution of strain during cracking and healing was measured in real time using digital image correlation. Favorable alignment and strong ionic bonding across the interface of partially fractured crystals facilitate self-healing. This study elevates organic crystals close to the best-in-class self-healing polymers and sets an approach for durable crystal-based optoelectronics.

The Photosalient Effect and Thermochromic Luminescence Based on o-Carborane-Assisted π-Stacking in the Crystalline State

Herein, we report the unique multiple-stimuli responsiveness of anthracene-tethered o-carborane derivatives. We designed and synthesized anthracene derivatives with different substitution positions and numbers of the o-carborane units. Two compounds had characteristic crystal structures involving the columnar π-stacking structures of the anthracene units. From the analysis of crystalline-state structure-property relationships, it was revealed that the crystals exhibited the photosalient effect accompanied by photochemical [4+4] cycloaddition reactions and temperature-dependent photophysical dual-emission properties including excimer emission of anthracene. Those properties were considered as non-radiative and radiative deactivation pathways through the excimer formation in the excited state and the formation of excimer species was facilitated by the π-stacking structure of anthracene units. Moreover, we found unusual temperature dependency on the occurrence of the photosalient effect. According to the data from variable temperature X-ray crystallography, a strong correlation between lattice shrinkage and strain accumulation is suggested.

Photoinduced Puffing with Large Volume Expansion and Photomechanical Motions induced by Topochemical [4+4] Reactions in Molecular Crystal Solvates

In this work, we report the first example of two crystal solvates of an anthracene-benzhydrazide based molecule (Ant) that display very distinct photo-responsive behaviour when 365 or 405 nm or visible light is illuminated. For the first time, the crystal hydrate that has water molecule in the lattice (hereafter named as Ant-H2O) display fascinating puffing behavior with large volume expansion upto 50 % accompanied with surface modulation when illuminated with 405 nm light, a phenomenon very much similar to the rice or popcorn puffing by thermal treatment. Utilizing the properties of photoconverted Ant-H2O crystals, we have demonstrated their application in photoinduced enhanced liquid absorption using various liquids/solutions. The other crystal solvate having DMF in the crystal lattice (hereafter named as Ant-DMF) responds to 405 nm light by bending, twisting, chopping, jumping or splitting etc. The chopping of Ant-DMF crystal was also observed under ambient/white light but at a slower rate compared to 405 nm light. Single crystal X-ray diffraction study reveals that the photoinduced puffing and photomechanical effects of these materials are rooted to the topochemical [4+4] cycloaddition reaction between the anthracene moieties that facilitate molecular packing change assisted by the reconfiguration of intermolecular non-covalent interactions involving lattice trapped solvent molecules.

Mechanochromic aromatic hydrocarbons that bear one simple substituent

Structurally simple aromatic hydrocarbons that possess only one isocyano group show luminescent mechanochromism. The structural isomers of these aromatic hydrocarbons exhibit blue- and red-shifted emission bands upon mechanical stress. Their low molecular weight enables their sublimation under mild conditions.

Thermosalient effect of a naphthalene diimide and tetrachlorocobaltate hybrid and changes of color and magnetic properties by ammonia vapor

An organic-inorganic hybrid metal halide (OIMH), namely the electron-deficient naphthalene diimide (NDI) and [CoCl₄]^2- hybrid (1), showed potential as a sensor for ammonia and amines, in addition to magnetic changes upon vapochromism. Crystal 1 exhibited thermosalient behavior such as leaping and movement, at around 130 °C, which could be explained to be associated with the removal of water molecules from the crystal lattice as shown by TGA and DSC. Compound 1 changed from green to black within 5 minutes when exposed to ammonia vapor, which was attributed to the radical formation in the NDI moiety as evidenced by ESR, and this phenomenon was preserved even when other mono- and di-alkylamines were applied. The exposure of 1 to ammonia resulted in a subsequent color alteration, progressing from black to a gradually dark orange after one day (1_NH3_1 day). This transformation was concomitant with the formation of [Co(NH₃)₆]³⁺ from [CoCl₄]^2-, leading to a modification of the magnetic properties from paramagnetic Co(II) (S = 3/2) to diamagnetic Co(III) (S = 0). Based on these findings, compound 1 represents the first example of an OIMH that exhibits thermosalient behaviour, color change, and magnetic conversion upon exposure to ammonia.

Photomechanical crystalline materials: new developments, property tuning and applications

This highlight gives an overview of the mechanism development, property tuning and application exploration of photomechanical crystalline materials.

Photoresponsive gadolinium-anthracene complexes: tuning the orientation and π-π stacking of anthracene groups via alkyl ester substituent of the phosphonate ligand

Controlled assembly of metal-anthracene complexes is important for the development of smart photoresponsive materials based on [4+4] anthracene photocycloaddition reactions. Here, we report three mononuclear complexes containing two anthracene units,...

Thermosalience coupled to abrupt spin crossover with dynamic ligand motion in an iron(II) molecular crystal

Here we report an iron(II) molecular crystal that show thermosalient effect (crystal jumping) coupled to cooperative high-spin (HS) to low-spin (LS) spin crossover (SCO). The new iron(II) compound [Fe(LPh,Et)2(NCS)2] (LPh,Et...