Printable Off–On Thermoswitchable Fluorescent Materials for Programmable Thermally Controlled Full‐Color Displays and Multiple Encryption

Abstract Thermoswitchable fluorescent materials (TFMs) have received special attention due to their unique fluorescent colorimetric responses to temperature. Conventional TFMs generally display unicolor with switching from one color to another, showing unprintable and unsatisfied performances. These limitations greatly hinder their development and expansion toward advanced applications. Herein, the superior integration of full‐color, off–on switching mode, printability, and high performance to TFMs is achieved successfully. The success is due to a thermally induced synchronous “dual/multichannel” stimulus–response mode regulated by a self‐crystalline phase‐change material; that is, synergistic changes of the molecular existence states and subsequent colors/spectra of the fluorescent modifier and fluorophores, accompanied by corresponding high‐efficiency on–off switching of Förster resonance energy transfer. These TFMs are simple to prepare and show good performance, such as high fluorescence emission contrast (>100), great reversibility (>200 cycles), and easy‐to‐adjust response temperature. Particularly, these R/G/B TFMs can be prepared as tricolor fluorescent inks, and thus full‐color emissions on flexible substrate can be easily obtained by printing. Finally, their great potential in switchable dynamic interior decoration, programmatic temperature‐control information display, and senior information encryption are illustrated. This successful exploration offers a new perspective for designing and optimizing various other switchable materials with higher comprehensive performances.