Hysteretic Control of Near‐infrared Transparency Using a Liquescent Radical Cation

Needlestick-Stimulation-Induced Conversion of Short-Wave Infrared-Light Transparency Using a Liquescent Radical Anion

A liquescent salt consisting of a 7,7,8,8-tetracyanquinodimethane (TCNQ) radical anion and a tetra-n-decylammonium ion, 1+•TCNQ•-, exhibits rapid changes in the short-wave infrared (SWIR) light transparency at 1000-1400 nm upon the application of a one-shot needlestick-stimulus. Radical anion salt 1+•TCNQ•- transforms from a blue solid to a green liquid at 90 °C without decomposition under aerated conditions, and remains in the liquid state upon cooling to 70 °C. After applying pressure with a needlestick on a cover glass at 70 °C, the liquid transforms rapidly into the solid state over a timescale of seconds across a centimeter scale of area. Along with the liquid-solid transition, the SWIR-light transparency at 1200 nm completely switches from the "on" to the "off" states. Experimental results, such as electronic spectra and crystal structure analysis, indicates that the SWIR-light absorption in the solid state is due to the existence of a slipped-stacking π-dimer structure for TCNQ•-. The rapid rearrangement is induced by the formation of the π-dimer structures from the monomers of TCNQ•- and the subsequent generations of the solid-state seed.

Temperature-Dependent Modulation of Short-Wave-Infrared Light Transparency Based on Associated Structures of a Liquescent Nickel(III) Complex

A liquescent bis(malononitriledithiolato)nickel(III) complex with a bis(methoxyethyl)imidazolium cation, 1[Ni(mnt)2 ], exhibits three-stage thermochromic modulation of transparency/absorption in the short-wave-infrared (SWIR) region (1000-2500 nm), driven by associated structural changes. Upon heating, the electronic spectra of 1[Ni(mnt)2 ] in the SWIR region shift to shorter wavelengths accompanying with the solid-liquid phase transition at 76 °C. Further heating to over 109 °C induces a second transition of the electronic spectra, characterized by a blue-shift of the SWIR absorption in the liquid phase. The results of temperature-dependent electronic spectra and magnetic susceptibility indicated that the thermochromic changes can be attributed to the two-step dissociation of the associated structures of [Ni(mnt)2 ]- , occurring during the solid-liquid phase transition and the shift of dimer-monomer equilibrium in the liquid state. These changes can be visualized using an SWIR imaging camera under appropriate SWIR lights.

Rapid Luminescent Enhancement Triggered by One-shot Needlestick-stimulus Using a Liquescent Gold(I) Salt

Luminescence from a gold(I) complex with an N-heterocycliccarbene-based ligand, 1⁺ ⋅NTf₂ ^- , increased rapidly upon the application of one-shot needlestick-stimulus. The weakly orange-emitting solid-state of 1⁺ ⋅NTf₂ ^- was prepared by cooling its melted liquid to 90 °C. Upon applying a weak pinpoint stimulus with a needle, this weakly orange-emitting solid state transformed into an intensively violet-blue-emitting state on a timescale of seconds. The emission after applying the stimulus could be visualized upon UV excitation even under ambient room light. This sequential phase transition from a stable solid to a liquid and then to a metastable solid could occur repeatedly without any measurable degradation of the complex. Various shapes could be prepared by casting the liquid-state complex into molds of different designs. This rapid response is thought to be triggered by the flexible intermolecular interactions in the kinetically generated aggregates formed upon cooling the liquid state, and by the strong Au-Au interactions in the thermodynamically stable crystals after applying the needlestick-stimulus.