Photochromic Tungsten Oxide Quantum Dots-based Fluorescent Photoswitches towards Dual-mode Anti-counterfeiting Application

Development of new anti-counterfeiting technology to increase the difficulty of imitation and decoding is becoming increasingly important, but still remains challenging yet. In this work, we report the design of new fluorescence photoswitches based on photochromic tungsten oxide quantum dots (WO 3 QDs) for dual-model anti-counterfeiting applications. Complexing photochromic WO 3 QDs with fluorescent gold nanoclusters (AuNCs) enables the construction of a photoswitchable fluorescence system (WO 3 -AuNCs) based on fluorescence resonance energy transfer. Detailed spectral and photophysical characterization showed that WO 3 QDs well-retain the photochromic properties within the WO 3 -AuNCs composite. Importantly, photoresponsive and highly reversible switching of both color and fluorescence signals was successfully achieved by simply alternating the irradiation with UV and visible light. Potential utility of photoswitchable WO 3 -AuNCs composite as novel dual-model anti-counterfeiting materials has been successfully demonstrated, including photoswitchable ink, rewritable paper and number encryption. Compared with other anti-counterfeiting materials, the present photochromic WO 3 QDs-based fluorescent switches are easily synthesized and handled, and they can provide dual security mode (color and fluorescence). This work provides a generable WO 3 QDs-assisted strategy of fabricating advanced fluorescence photoswitches for versatile optical counterfeiting applications.