Single‐Sample Ratiometric Organic Films for Naked‐Eye High‐Temperature Multi‐Threshold Indication

Abstract Threshold temperature sensors are crucial for recording the thermal histories of environments under different scenarios. However, most organic threshold thermometers are not suitable for high‐temperature indication due to significant thermo‐facilitated emission quenching. Here, a series of ratiometric luminescent high‐temperature threshold organic film indicators have been realized by synergetic effects of intramolecular local excited to charge transfer states and disaggregation from excimer to monomer. Varying the polymer matrixes with different glass transition temperatures effectively tunes the threshold sensing temperatures. More importantly, the wide sensing span of the high‐temperature region enables the single‐sample films (in one kind of polymer matrix) to achieve multiple temperature threshold indications, directed only by multiple naked‐eye emission color changes. These drop‐casting organic film thermometers indicate great potential in robust and low‐cost outdoor applications, as well as large‐area and flexible threshold temperature sensing.