Temperature-responsive carbon dots-spiropyran photochromic films for stepwise-decryption optical anti-counterfeiting with information self-destruction

A Novel Mechanistic Insight: Heat disrupts CDs-SP bonds irreversibly, lowering FRET for thermal-memory photochromism & self-erasing encryption. • A Simple yet Powerful Material System: Enables photo/thermal dual tuning via irreversible temperature-tuned H-bond/FRET modulation, with thermal memory. • Cutting-Edge Applications: A “stepwise decryption-self-destruction” dual system boosts optical anti-counterfeiting anti-cracking & non-replicability. Photochromic materials are promising for advanced optical anti-counterfeiting and dynamic information encryption. However, traditional spiropyran (SP)-based solid films suffer from low photoswitching efficiency, poor cycling stability, and single stimulus response. Herein, a temperature-memory photochromic composite film (CDs-SP-PMMA) was fabricated via a simple solution-casting method. The hydrogen-bond network between CDs and SP enhances SP photoisomerization and enabled efficient Förster resonance energy transfer (FRET) from CDs to the open-ring MC state. Preparation temperature irreversibly modulated hydrogen-bond structure and FRET efficiency, endowing the film with unique temperature-memory properties. The 30 °C film showed obvious green-to-orange-red fluorescence switching, while the 70 °C film only exhibited weak color change. The composite film presented excellent reversible photoswitching and cycling stability. Based on its temperature-dependent optical response, it was successfully applied in stepwise-decryption anti-counterfeiting and self-destructive information encryption. This work offered a novel design concept for multi-stimuli-responsive photochromic materials. By regulating hydrogen-bond structures and photoresponsive properties through temperature control, it effectively improved the color-changing performance of materials and further promoted the practical application of such materials in high-end information security and intelligent optoelectronic devices.