Ionic liquid as plasticizer for europium(iii)-doped luminescent poly(methyl methacrylate) films

Abstract

Flexible luminescent polymer films were obtained by doping europium(III) complexes in blends of poly(methyl methacrylate) (PMMA) and the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C₆mim][Tf₂N]. Different europium(III) complexes have been incorporated in the polymer/ionic liquid matrix: [C₆mim][Eu(nta)₄], [C₆mim][Eu(tta)₄], [Eu(tta)₃(phen)] and [choline]₃[Eu(dpa)₃], where nta is 2-naphthoyltrifluoroacetonate, tta is 2-thenoyltrifluoroacetonate, phen is 1,10-phenanthroline, dpa is 2,6-pyridinedicarboxylate (dipicolinate) and choline is the 2-hydroxyethyltrimethyl ammonium cation. Bright red photoluminescence was observed for all the films upon irradiation with ultraviolet radiation. The luminescent films have been investigated by high-resolution steady-state luminescence spectroscopy and by time-resolved measurements. The polymer films doped with β-diketonate complexes are characterized by a very intense ⁵D₀ → ⁷F₂ transition (up to 15 times more intense than the ⁵D₀ → ⁷F₁) transition, whereas a marked feature of the PMMA films doped with [choline]₃[Eu(dpa)₃] is the long lifetime of the ⁵D₀ excited state (1.8 ms).