Fabrication of Flexible High‐Temperature Film Thermometers and Heat‐Resistant OLEDs Using Novel Hot Exciton Organic Fluorophores

Abstract The development of organic thermosensitive fluorophores for use in heat‐resistant organic light emitting diodes (OLEDs) and large‐area and flexible high‐temperature sensing remains challenging due to the susceptibility of such materials to thermally facilitated nonradiative decay. A series of “hot exciton” materials (“C1” and “C2”) based on pyrrole‐substituted triarylphosphine oxides that exhibit high heat resistance have been developed. At a temperature of 260 °C, the films retain 42% (C1) and 29% (C2) of their room temperature fluorescence. This is thanks to thermally facilitated reverse intersystem crossing (RISC) from a high‐lying triplet to a singlet state. By combining the novel fluorophores with a yellow emitter with an extremely large Stokes shift, flexible and large‐area ratiometric film thermometers are fabricated that demonstrate naked‐eye high‐temperature sensing. The relative sensitivity, S r , of the film thermometer is higher than 1% K –1 in the high‐temperature region (393 to 470 K), with the maximum S r reaching 1.26% K −1 at 430 K. Using these blue emitters, heat‐resistant cyan and white OLEDs are also fabricated. With thermally populated singlets and nearly 100% exciton harvesting via fast RISC, the C1‐based cyan OLED exhibits a nearly 12‐fold enhancement in electroluminescence on heating from room temperature to 530 K, while the corresponding white OLED displays a 5.7‐fold electroluminescence enhancement.