Light-Responsive Fluorescent Security Ink Based on Calixpyridinium-Protoporphyrin IX Disodium Salt Supramolecular Nanoassemblies

In this work, the coordination effects of protoporphyrinIX disodiumsalt (PpIX) with Cu-II, Fe-II, and Zn-II were systematically studied, and the host-guest interactionsof calixpyridinium with PpIX and the three metalloporphyrins werefurther explored. The bonding ratio between calixpyridinium and PpIXwas different from that between calixpyridinium and the other threemetalloporphyrins. The reduction of the electronegativity of PpIXcaused by the coordination of metal cations may be the reason forthe change of the bonding ratio. The reduction of the electronegativityof PpIX caused by the coordination of metal cations also leads toa weaker host-guest interaction with calixpyridinium. The supramolecularnanoassemblies prepared by the host-guest interactions of calixpyridiniumwith PpIX and the three metalloporphyrins under alkaline conditionscould emit a bright fluorescence due to the pH-dependent luminescencecharacteristics of calixpyridinium and PpIX. Among calixpyridiniumand the three metal ions, calixpyridinium alone had the best effecton promoting the photoactivity of PpIX. Its fluorescence graduallydisappeared after being irradiated by an incandescent lamp not onlyin aqueous solution but also on a filter paper. More interestingly,the supramolecular nanoassemblies formed by calixpyridinium and thephotoreaction product of PpIX had a reversible temperature responsiveness,which could lead to a reversible fluorescence on-off control.As a result, this material was successfully applied as an intelligentlight-responsive fluorescent security ink.

Automated summary

In this study, the coordination effects of protoporphyrin IX disodium salt (PpIX) with Cu-II, Fe-II, and Zn-II were investigated, along with the host-guest interactions of calixpyridinium with PpIX and the three metalloporphyrins. The bonding ratio between calixpyridinium and PpIX differed from that with the other metalloporphyrins due to the reduction of the electronegativity of PpIX caused by the coordination of metal cations. Moreover, the supramolecular nanoassemblies formed by the host-guest interactions exhibited a reversible temperature responsiveness, allowing for reversible fluorescence on-off control and potential application as an intelligent light-responsive fluorescent security ink.