An AIEgen-based luminescent photo-responsive system used as concealed anti-counterfeit material

Photo-responsive materials with good luminescence performance in solid state have received widespread attention. However, the reported luminescent photo-responsive systems exhibit either only color change or both color and luminescence changes in solid state upon UV light irradiation. Developing photo-responsive materials with only tunable luminescence signals in solid state remains a great challenge for constructing concealed anti-counterfeit materials. In this work, a novel luminescent photo-responsive molecule (TPE-TS) was developed, which exhibited intense fluorescence emission due to the aggregation-induced emission (AIE) characteristic from its tetraphenylethene moiety. After irradiated by UV light, an isomerization from thio-keto form to thio-enol form took place in the thiosemicarbazide group, accompanied with obvious fluorescence quenching. Interestingly, there was no visible color variation before and after UV light irradiation owing to the small conjugated structure of TPE-TS. Taking this unique photo-responsive property, a concealed anti-counterfeit paper was successfully prepared. Letters could be recorded by UV light on this paper, hided under daylight and only visible again by UV light, demonstrating an excellent concealed performance as an anti-counterfeit material.