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

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Optoelectronics

Background:

• Developing stimuli-responsive materials is crucial for advanced optical applications.
• Controlling light transparency with external triggers remains a significant challenge in materials science.

Purpose of the Study:

• To investigate the rapid optical switching behavior of a liquescent salt upon mechanical stimulus.
• To elucidate the structural basis for the observed changes in short-wave infrared (SWIR) light transparency.

Main Methods:

• Synthesis and characterization of a liquescent salt: 7,7,8,8-tetracyanquinodimethane (TCNQ) radical anion with a tetra-n-decylammonium ion.
• Investigation of phase transitions (solid-liquid) induced by temperature and mechanical stress (needlestick).
• Measurement of SWIR light transparency changes (1000-1400 nm) correlated with phase transitions.
• Analysis of electronic spectra and crystal structures to understand the optical properties.

Main Results:

• The liquescent salt (1⁺•TCNQ^•-) exhibits a reversible solid-liquid transition at 90°C and remains liquid upon cooling to 70°C.
• A needlestick stimulus at 70°C rapidly induces a liquid-to-solid transition over a centimeter scale within seconds.
• This phase transition results in a complete switch of SWIR light transparency at 1200 nm from 'on' to 'off'.

Conclusions:

• The observed SWIR light absorption in the solid state is attributed to the formation of slipped-stacking π-dimer structures of TCNQ radical anions.
• The rapid rearrangement is triggered by the formation of these π-dimers from monomers, initiating solid-state seeding.
• This study demonstrates a novel, mechanically triggered optical switching material with potential in optoelectronic devices.