Three‐Output Naked‐Eye High Temperature Organic Film Threshold Thermometers Based on Non‐Invasive Chemical Reaction

Abstract 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.