Photochromic Polyurethane Coatings with Cross‐Linked Structure and Self‐Healing Behavior Based on the FRET Effect

Intelligent fluorescent coatings have received widespread attention in the encryption technique field such as anti-counterfeit, while the traditional fluorescent coatings are easy to be damaged by external force. In this study, the fluorescent and self-healing anti-counterfeit coatings are prepared after rational molecular design. Two polymers containing fluorescent groups, including polyurethane containing the anthracene (AN) side group and polyimide containing the naphthalenediimide (NDI) structure are synthesized to realize multiple color changes with fluorescence through simply blending. Due to the overlapping fluorescence spectra of the groups, enabling the fluorescence resonance energy transfer effect (FRET), the coating with different group ratios exhibits tunable fluorescence under the same excitation light, providing diverse patterns. Moreover, due to the reversible photo-crosslinking and thermal de-dimerization properties of anthracene, the recording, erasure, and rewriting of the surface pattern can be realized, and the fluorescent anti-counterfeit coatings exhibit excellent self-healing properties after cross-linking due to the FRET effect, which solves the problem of poor healing and ensures the stability and integrity. The fluorescent coating with cross-linked structure and self-healing behavior based on the FRET effect greatly expands the functional applications of traditional polyurethane materials.