Exciton Recycling for Heat‐Resistant Arylphosphine Oxides With Dual Thermal Response: High‐Contrast Thermochromism and Precision Ratiometric Sensing

The development of high‐performance luminescent thermosensors capable of dual threshold/temperature detection using a single emitter material presents a significant challenge in high‐temperature applications. Herein, we report two thermally stable blue‐emitting pyrenyl phosphine oxide isomers diphenyl(6‐(4‐(9‐phenyl‐9H‐fluoren‐9‐yl)phenyl)pyren‐1‐yl)phosphine oxide (P‐TPSPyPO) and diphenyl(6‐(3‐(triphenylsilyl)phenyl)pyren‐1‐yl)phosphine oxide (M‐TPSPyPO) that uniquely combine threshold thermal alert with precise temperature sensing capabilities. At high concentrations, these materials exhibit a remarkable excimer‐to‐monomer transition at 393 K, demonstrating exceptional relative sensitivities of 140% K −1 (P‐TPSPyPO) and 48% K −1 (M‐TPSPyPO) accompanied by distinct luminescence color changes for threshold detection. When employed as ratiometric thermometers at low doping concentrations, they maintain broad operational ranges (P‐TPSPyPO: 314–593 K; M‐TPSPyPO: 312–560 K) in ambient air with temperature sensitivities (S r ) both exceeding 0.6% K −1 . The materials achieve peak S r values of 2.1% K −1 at 463 K (P‐TPSPyPO) and 1.9% K −1 at 461 K (M‐TPSPyPO), representing state‐of‐the‐art performance for luminescent thermometers. Their practical utility is demonstrated through high‐resolution thermal mapping across large areas (4 × 4 cm 2 ) and effective implementation in multilevel anti‐counterfeiting systems.