Achieving Efficient Thermometer‐Like Organic Aggregates Through Regulation of Thermally Activated Delayed Fluorescence to Fluorescence

ABSTRACT Precise temperature monitoring is critical for numerous practical applications, driving the development of high‐performance luminescent thermometers. Luminescent crystalline thermometers based on thermochromic principles have attracted considerable attention due to their superior sensitivity, broad temperature adaptability, and stable luminescent quantum yields. Herein, we report a solid‐state luminescent colorimetric thermometer based on a rationally designed and synthesized thermally activated delayed fluorescence (TADF) crystalline material, featuring remarkable thermosensitive hue transformation and intense emission over a wide temperature range of 270–460 K. The fabricated thermometer achieves an ultrahigh temperature accuracy (<1 K) and a 27‐fold magnification of the energy difference. Photophysical and structural characterizations reveal that the loosely packed molecular arrangement in TADF aggregates not only ensures high emission efficiency but also provides sufficient space for thermally induced molecular conformational changes. Additionally, the emission color can be reversibly switched from blue to green upon solvent stimulation, with excellent repeatability and photostability. This work provides a promising strategy for the design of high‐sensitivity TADF‐based thermometers, advancing the development of novel thermochromic luminescent materials for non‐contact temperature visualization.