frameworks, [36][37][38] quantum dots, [39][40] organic dyes, [41][42][43][44][45][46][47][48][49][50][51] polymers, [5,[52][53] and biomolecules. [54] Organic luminophores exhibit tremendous promise in constructing solid film temperature sensors, [36,[55][56] benefiting from many advantages of large-area in situ thermomapping attributed to their intrinsic flexibility, precisely tunable photophysical properties by easy tailoring of molecular structures, as well as real-time sensing due to nano/micro-second timescale luminescence decay. [1,2,[4][5][6][7]13,14,19] However, the deleterious problem of thermally facilitated emission quenching hinders their applications for wide-range and high-temperature sensing. This is because the nonradiative deactivation at heating is mostly inevitable. Thus, it is of prime importance to develop heat-resistant organic luminophores to realize hightemperature luminescent film thermometers.In general, thermosensitive luminophores exhibit characteristic thermal responses stemming from their temperature-dependent photophysical dynamics, including changes of emission intensity, wavelength, and lifetime. Ratiometric thermometry presents a more reliable and accurate measurement by monitoring the temperature dependence of emission intensity ratio between two separate emissions. This is attributed to their advantageous self-reference sensing, which is resistant to luminophore concentration, fluctuation of excitation source or detector, and luminescence background. [2,57] The method for implementing ratiometric luminescent thermometry commonly relies on energy-transferred emitting systems consisting of two emitters with distinctive temperature responses. The excitation energy is partially transferred from an excited donor (short-wavelength emitter) to an acceptor molecule (long-wavelength emitter), leading to coexistence of the donor and acceptor emissions. [57][58][59] However, the energy transfer efficiency is also affected by temperature, because heating may increase the distance between molecules and influence the intermolecular interactions. [60] That means the energy-transfer strategy would suffer from severe interference between the two emitters. Therefore, in hybrid systems the original marked difference in their thermal responsiveness would largely be compromised. [61][62] Consequently, the Energy transfer is usually applied in ratiometric thermometry, but it often decreases sensitivities due to much reduced distinguishment in the thermal responses of two different-colored emitters. Herein, a feasible strategy to restrain energy transfer is utilized for achieving sensitive high-temperature detection, simply by increasing the dopant concentration to induce microphase separation. Atomic force microscopy phase images reveal that this phase separation becomes dominant when the doping ratio reaches above 40%. This results in suppression of energy transfer, which is evidenced by systematic photophysical investigations. On this basis, by using heatresistant emitters, a series of inexpensiv...
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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