Concentration‐Induced Phase Separation to Suppress Energy Transfer for High‐Temperature Ratiometric Sensing in Organic Films

Abstract 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 heat‐resistant emitters, a series of inexpensive and easily prepared solid‐film organic high‐temperature ratiometric thermometers are developed. They exhibit a broad eye‐detective sensing range of 102–236 °C with the relative sensitivity (S_r) higher than 0.5% K⁻¹ and the maximum temperature resolution attaining 0.39 K. Good reversibility and stability are also demonstrated in ambient atmosphere.