Terbium based (poly)ionic liquids for anti-counterfeiting and droplet manipulation

Abstract

Rare earth elements show unique optical and magnetic properties, with great potential in sensing, imaging, light harvesting, and magnetically responsive materials. In this study, a typical lanthanide terbium based ionic liquid, vinylimidazolium tetranitroterbium (Vim[Tb(NO₃)₄]), and the corresponding polymer, poly(vinylimidazolium tetranitroterbium) (PVim[Tb(NO₃)₄]), are synthesized by introducing terbium into conterions. Vim[Tb(NO₃)₄] and PVim[Tb(NO₃)₄] are characterized by ¹H NMR and negative ion mass spectroscopy. Magnetic property tests show that the monomer and polymer are paramagnetic, and the susceptibility of PVim[Tb(NO₃)₄] is higher than that of Vim[Tb(NO₃)₄]. The corresponding aqueous droplets are deformed by an external magnetic field, and the contact angle changes with the magnetic field intensity and direction, changing the surface tension as a result. Meanwhile, the magnetic monomer and polymer show bright fluorescence under ultraviolet excitation, while there is no color under sunlight. Vim[Tb(NO₃)₄] exhibits stronger fluorescence than PVim[Tb(NO₃)₄] in solution, while pure PVim[Tb(NO₃)₄] exhibits stronger fluorescence than pure Vim[Tb(NO₃)₄]. Noncontact manipulation of aqueous droplets in a dark enviroment is favored for special applications under a strong magnetic field. Therefore, Vim[Tb(NO₃)₄] exhibits better fluorescence performance in solution, while PVim[Tb(NO₃)₄] is more suitable for anti-counterfeiting applications and droplet manipulation.