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.
High‐contrast and stably visualized ambient or luminescent color‐switching can be achieved by thermal‐induced non‐invasive chemical reaction for naked‐eye threshold temperature indication. The clear and visible output signal of these indicators arises from the large absorption/emission spectral changes upon heating. However, such chemical reactions are difficult to realize in solid‐state, especially in the high‐temperature region. Herein, a series of naked‐eye high‐temperature threshold film indicators have been developed based on the solid‐state in situ thermal decomposition reaction of difluoroboron β‐diketonate derivative. These thermosensitive films feature three high‐contrast visible outputs of ambient thermochromism, fluorescence color change, and luminescence ON/OFF switching, which can be easily detected with the naked eye. The PR‐PS film of (E)‐4‐(2‐(6‐bromopyren‐1‐yl)vinyl)‐2,2‐difluoro‐6‐phenyl‐2H‐1λ3,3,2λ4‐dioxaborinine (PR) doped in polystyrene (PS) polymer matrix achieved high sensitivities related to change of ratiometric luminescence and fluorescence intensity up to 230%°C−1 and 1.85%°C−1, respectively. Furthermore, the polymer matrix with different glass transition temperatures enables programmable tuning of threshold temperature from 120 to 180 °C. These thermosensitive films show clear and high‐contrast color changes and emission turn‐off in real‐time with consistent air stability, high photostability, and waterproofing property. This shows considerable potential in outdoor robust high‐temperature threshold sensing and information storage.
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