Ultrastable Viologen Ionic Liquids-Based Ionogels for Visible Strain Sensor Integrated with Electrochromism, Electrofluorochromism, and Strain Sensing

Flexible electronics play a key role in the development of human society and our daily activities. Currently they are expected to revolutionize personal health management. However, it remains challenging to fabricate smart sensors with high robustness, reliability, and visible readout. Herein, high-performance electrochromic (EC), electrofluorochromic (EFC), and double-network ionogels with excellent transmissivity, high mechanical robustness, and ultrastable reversibility are prepared by combination of thienoviologen-containing ionic liquids with poly(ethyl acrylate) elastomer. The ionogels exhibit good mechanical properties (1000% stretchability and 3.2 kJ m⁻² fracture energy). The ionogel-based EC devices have a significantly simplified device fabrication process as well as superior cycling stability in which 88% of the contract ratio is maintained at 88% at 500 cycles, even after being stored for 2 years under ambient atmosphere (relative humidity: 30%∼40%, 25 °C). The conductivity of ionogels showed a fast and reproducible response to strain, and the conductivity decreased with increased strain. By virtue of the EC and EFC properties of the thienoviologen component, the EC and EFC efficiency decreased with the increased strain loaded on the ionogels, and almost no EC or EFC phenomena were observed when the strain was above 300%. This feasible strategy provides an opportunity for the development of visible strain sensors to monitor the body’s movements through color and fluorescence emission.