Multiple Dynamic Anticounterfeiting Using Photochromic Luminescence Organic Cocrystals

Photochromic and luminescent complexes are easy to imitate due to their single-signal output, resulting in a low encryption and anticounterfeiting level. Photochromic luminescence (PCL) complexes exhibit fluorescence and color-changing dual output, which provides additional safety and greatly improves anticounterfeiting security. However, it is challenging to overcome the competition between luminescence and the quenching effect of the photoinduced electron transfer (PET) process. This work proposes that introducing a highly conjugated luminescent unit into a photochromic molecule and using hydrogen bond interactions to construct highly rigid organic cocrystals is an effective strategy to overcome the quenching effect of PET in the construction of PCL compounds. By this strategy, two viologen-based cocrystals with fluorescence and color-changing dual output were synthesized, and high-security anticounterfeiting was demonstrated. The mechanistic analysis indicates that the highly conjugated compound not only significantly enhances the luminescent intensity but also prolongs the lifetime of the charge separated state, with its influence dominating over the quenching effect of the PET process. This work presents a strategy for constructing PCL complexes for high security anticounterfeiting.