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.