Tuning and reviving the luminescence of a new class of pyridyl β-diketonate Eu(III) metallomesogens: From molecules to entrapment in polymer particles

Abstract

A new class of polynuclear Eu(III) compounds bearing pyridyl β-diketonate ligands have been synthesised, and their thermal and photophysical behaviour studied. Since they behave as highly emissive materials, polymer thin films were prepared by using the Eu(III) compounds as a dopant and poly(methyl methacrylate) as the matrix. Interestingly, the luminescence properties of the new materials can be tuned by protonation of the nitrogen atom at the pyridine moiety of the ligands, which allows controlling the energy transfer between the antenna ligands and the Eu(III) centre. This stimuli-responsive luminescence behaviour causes a drastic colour change from red to green that can be useful to detect highly acidic media. The antenna effect has been also explored at the nanoscale. Several colloidal dispersions of poly(methyl methacrylate) microparticles encapsulating the luminescent Eu(III) compounds have been obtained from oil-in-water droplets. The polymer matrix acts as a barrier and protects the coordination environment of the Eu(III) compounds, avoiding the quenching effect by water coordination. This method of entrapment can constitute a powerful tool to revive the luminescence of Eu(III) species in aqueous media.