Non-Phase-Transition Luminescence Mechanochromism of a Copper(I) Coordination Polymer

A copper­(I) coordination polymer, [Cu₂I₂<b>L</b>₂]_<i>n</i> (CP <b>1</b>), shows luminescence mechanochromism with a color change from greenish-blue to yellow upon the application of pressure. Powder X-ray diffraction and Raman studies reveal that the changes in the bond lengths in crystalline CP <b>1</b> are the main cause of luminescence mechanochromism. The luminescence mechanochromic process of CP <b>1</b> preserves its crystallinity with a small lattice distortion, despite very high pressure, and it is a non-phase-transition process. After the addition of several drops of acetonitrile to the ground and compressed samples, the original greenish-blue emissive and crystalline states are restored. Therefore, the luminescence color conversion processes are fully reversible

Non-Phase-Transition Luminescence Mechanochromism of a Copper(I) Coordination Polymer

A copper­(I) coordination polymer, [Cu₂I₂<b>L</b>₂]_<i>n</i> (CP <b>1</b>), shows luminescence mechanochromism with a color change from greenish-blue to yellow upon the application of pressure. Powder X-ray diffraction and Raman studies reveal that the changes in the bond lengths in crystalline CP <b>1</b> are the main cause of luminescence mechanochromism. The luminescence mechanochromic process of CP <b>1</b> preserves its crystallinity with a small lattice distortion, despite very high pressure, and it is a non-phase-transition process. After the addition of several drops of acetonitrile to the ground and compressed samples, the original greenish-blue emissive and crystalline states are restored. Therefore, the luminescence color conversion processes are fully reversible

Reversible Luminescence Vapochromism and Crystal-to-Amorphous-to-Crystal Transformations of Pseudopolymorphic Cu(I) Coordination Polymers

Four solvent-responsive one-dimensional copper­(I) coordination polymers (CPs), namely, {[Cu₄I₄<b>L</b>(MeCN)₂]­·CH₂Cl₂}_<i>n</i> (<b>1</b>), {[Cu₄I₄<b>L</b>(MeCN)₂]­·CHCl₃}_<i>n</i> (<b>2</b>), {[Cu₄I₄<b>L</b>(MeCN)₂]­·0.5<i>p</i>-xylene}_<i>n</i> (<b>3</b>), and [Cu₄I₄<b>L</b>­(MeCN)₂]_<i>n</i> (<b>4</b>), were prepared by reaction of CuI with <i>N</i>,<i>N</i>′-bis­[2-(cyclohexylthio)­ethyl]­pyromellitic diimide (<b>L</b>) via self-assembly under varying solvent conditions. CPs <b>1</b>–<b>4</b>, which are pseudopolymorphic supramolecular isomers derived from solvent molecules, are composed of Cu₄I₄ cubane clusters. The ligands in CPs <b>1</b>–<b>3</b> adopted a <i>syn</i>-conformation, whereas in CP <b>4</b> they were observed in the <i>anti</i>-conformation. This occurred via <i>syn</i> to <i>anti</i> transitions upon heating, followed by exposure to MeCN vapor. In addition, a reversible <i>anti</i> to <i>syn</i> transition was achieved by agitating in mixed organic solvents. It was shown that ligand transition from the <i>syn-</i> to the <i>anti</i>-conformation occurred through crystal-to-amorphous-to-crystal transformations. Furthermore, CPs <b>1</b>–<b>3</b> exhibited reversible solvent exchange and crystal transformation by exposure to vapors from volatile organic compounds

Controlled Reversible Crystal Transformation of Cu(I) Supramolecular Isomers

Four copper­(I) coordination polymers (CPs), {[CuI<b>L</b>]·CH₃CN]}_<i>n</i> (<b>1</b>), {[CuI<b>L</b>]·CHCl₃}_<i>n</i> (<b>2</b>), {[CuI<b>L</b>]·CH₂Cl₂}_<i>n</i> (<b>3</b>), and [CuI<b>L</b>]_<i>n</i> (<b>4</b>), were prepared by self-assembly reactions between CuI and (2-pyrazinylcarbonyl)­thiomorpholine (<b>L</b>). CPs <b>1</b>–<b>4</b> are interconnected by rhomboid Cu–I₂–Cu units. CPs <b>1</b> and <b>4</b> have one-dimensional loop-chain structures, and <b>2</b> and <b>3</b> adopt two-dimensional network structures. CPs <b>1</b>–<b>4</b> are pseudopolymorphic supramolecular isomers. CPs <b>2</b>′ and <b>3</b>′ are prepared by removal of solvate molecules from CPs <b>2</b> and <b>3</b>, which are polymorphic supramolecular isomers with CP <b>4</b>. Reversible crystal-to-crystal transformations were observed under appropriate conditions such as solvent or heat

Reversible Crystal Transformations and Luminescence Vapochromism by Fast Guest Exchange in Cu(I) Coordination Polymers

Six Cu­(I) coordination polymers (CPs)[Cu₂I₂<b>L</b>₂]_<i>n</i> (<b>1</b>), {[Cu₂I₂<b>L</b>₂]·2MeCN}_<i>n</i> (<b>2</b>), [Cu₄I₄<b>L</b>₂]_<i>n</i> (<b>3</b>), {[Cu₄I₄<b>L</b>₂]·CH₂Cl₂}_<i>n</i> (<b>4</b>), {[Cu₄I₄<b>L</b>₂]·CHCl₃}_<i>n</i> (<b>5</b>), and {[Cu₄I₄<b>L</b>₂]·C₆H₆}_<i>n</i> (<b>6</b>)were synthesized by self-assembly reactions of CuI and the flexible mixed N/S donor ligand 4-(2-(cyclohexylthio)­ethoxy)­pyridine (<b>L</b>). Single-crystal X-ray diffraction analyses reveal that these 1D CPs form sets of supramolecular isomers; <b>1</b> and <b>2</b> are based on Cu₂I₂ rhomboids, while <b>3</b>–<b>6</b> are based on cubane Cu₄I₄ clusters. Crystal-to-crystal transformations of CPs <b>1</b>–<b>6</b> were reversible under heat or in an appropriate solvent (acetonitrile, dichloromethane, chloroform, or benzene). In addition, crystal transformations between CPs <b>1</b> and <b>3</b> occurred through addition of <b>L</b> or CuI. Moreover, CPs <b>3</b>–<b>6</b> exhibited reversible guest exchange and crystal transformations on exposure to the vapor of volatile organic compounds and heat. Remarkably, a guest molecule was exchanged by other guest molecules in the vapor phase within very short times and without the use of acetonitrile as a solvent, which normally plays a key role in trapped solvent exchange experiments

Polypyrrole/Agarose-Based Electronically Conductive and Reversibly Restorable Hydrogel

Conductive hydrogels are a class of composite materials that consist of hydrated and conducting polymers. Due to the mechanical similarity to biointerfaces such as human skin, conductive hydrogels have been primarily utilized as bioelectrodes, specifically neuroprosthetic electrodes, in an attempt to replace metallic electrodes by enhancing the mechanical properties and long-term stability of the electrodes within living organisms. Here, we report a conductive, smart hydrogel, which is thermoplastic and self-healing owing to its unique properties of reversible liquefaction and gelation in response to thermal stimuli. In addition, we demonstrated that our conductive hydrogel could be utilized to fabricate bendable, stretchable, and patternable electrodes directly on human skin. The excellent mechanical and thermal properties of our hydrogel make it potentially useful in a variety of biomedical applications such as electronic skin

Large Work Function Modulation of Monolayer MoS₂ by Ambient Gases

Although two-dimensional monolayer transition-metal dichalcogenides reveal numerous unique features that are inaccessible in bulk materials, their intrinsic properties are often obscured by environmental effects. Among them, work function, which is the energy required to extract an electron from a material to vacuum, is one critical parameter in electronic/optoelectronic devices. Here, we report a large work function modulation in MoS₂ via ambient gases. The work function was measured by an <i>in situ</i> Kelvin probe technique and further confirmed by ultraviolet photoemission spectroscopy and theoretical calculations. A measured work function of 4.04 eV in vacuum was converted to 4.47 eV with O₂ exposure, which is comparable with a large variation in graphene. The homojunction diode by partially passivating a transistor reveals an ideal junction with an ideality factor of almost one and perfect electrical reversibility. The estimated depletion width obtained from photocurrent mapping was ∼200 nm, which is much narrower than bulk semiconductors

Babinet-Inverted Optical Yagi–Uda Antenna for Unidirectional Radiation to Free Space

Nanophotonics capable of directing radiation or enhancing quantum-emitter transition rates rely on plasmonic nanoantennas. We present here a novel Babinet-inverted magnetic-dipole-fed multislot optical Yagi–Uda antenna that exhibits highly unidirectional radiation to free space, achieved by engineering the relative phase of the interacting surface plasmon polaritons between the slot elements. The unique features of this nanoantenna can be harnessed for realizing energy transfer from one waveguide to another by working as a future “optical via”