Ultrahigh-sensitivity thermochromic smart fabrics and flexible temperature sensors based on intramolecular proton-coupled electron transfer

The ultrahigh-sensitivity temperature sensors and smart fabrics were prepared based on the new designed fluorane and microcapsule technology, which demonstrates ultralow-color-hysteresis, narrow color-change temperature range, and reversible rich color-change. • Ultrahigh-sensitivity smart wearable thermochromic fabrics and sensors were designed and fabricated. • Introducing intramolecular proton-coupled electron transfer into the thermochromic field, avoiding color-hysteresis. • Controllable color, adjustable response temperature and high precision temperature monitoring behavior. • Microencapsulation suitable for various substrate and large-scale industrialization. Ultrahigh-sensitivity including both ultralow-color-hysteresis and narrow temperature change is an important requirement of temperature sensors. However, it is an almost impossible challenge for the traditional ternary thermochromic mechanism. Herein, a new class of fluorane dyes was designed and synthesized which was used to fabricate the ultrahigh-sensitivity sensors and smart fabrics via microcapsule technology and screen printing. The new fluorane dyes (M2 and M3) performed excellent thermochromic properties with a narrow color-change temperature range (2.1 °C) and ultralow-color-hysteresis (<0.5 °C). The ultrahigh-sensitivity property is attributed to the intramolecular proton-coupled electron transfer (PCET) color-change mechanism. Moreover, the effect of particle size and core/shell ratio on the temperature sensitivity of microcapsule was investigated. The optimized microcapsules with 5 μm and 2/1 core/shell showed overall properties including the color-change temperature range as about 2 °C and the ultralow-color-hysteresis as about 0.3 °C. This unique design concept for ultrahigh-sensitivity sensors has great potential in human body care and other flexible sensors or smart fabrics fields.