Wide Color Gamut and High Sensitivity in Luminescent Thermal Indicators from an Organic Energy Donor‐Acceptor System with Tunable Molecular Interactions

Abstract The photoluminescent response of organic materials upon applied stimuli is a key property that can be easily utilized for their implementation in simple and inexpensive sensing devices. A wide spectral response together with an accessible detection constitutes two crucial features required for promising sensing materials. Here, a new energy donor‐acceptor intermolecular system in thin films is developed, realizing a gradual and irreversible change on the photoluminescent emission determined by the thermal history of the sample. These changes are principally induced in the excited state intramolecular proton transfer (ESIPT) type donor molecule that governs the overall interaction of the system as a consequence of the thermal events. Three main fluctuating channels of emission are observed, which are distinguished by the shifting of the acceptor emission and the relative intensity of all the spectral features. These effects are translated into a temperature responsive configuration that creates a widely tunable chromatic emission strictly consistent with its thermal history. The application of the thin films as wide range thermal indicators is demonstrated for simple visual inspection and for ratiometric sensing, showing noticeable color changes and remarkable sensitivities of over 14% °C⁻¹.