Luminescence modulation via cation–π interaction in a lanthanide assembly: implications for potassium detection

Abstract

Herein luminescent lanthanide supramolecular assemblies were constructed via coordination of a crown-connected bis-terpyridine (L₁) and Ln³⁺ ions, which can self-assemble to form homogeneous spherical nanoparticles with an average diameter of 700 nm on a silicon plate surface upon slow evaporation of solvents. Potassium ions are shown to give rise to obvious enhancement in the luminescence of Ln³⁺ (Ln = Eu, Tb) ions in the lanthanide assemblies. The changes are the consequence of the capture of the cations by the crown moieties via cation–π interactions, increasing the triplet excited energy level of L₁ and thus favoring the population of the lanthanide's excited state from the antenna triplet state by means of an energy transfer. Besides, energy transfer from Tb³⁺ to Eu³⁺ was observed in the luminescent Eu³⁺/Tb³⁺ bimetallic assemblies (Eu/Tb·L₁) and the efficiency can be tuned by potassium concentration. Thus, Eu/Tb·L₁ can serve as a self-calibrating sensor, which can selectively and quantitatively detect potassium by linearly correlating the K⁺ concentration to the emission intensity ratio of ⁵D₄ → ⁷F₅ transition (Tb³⁺) to ⁵D₀ → ⁷F₂ transition (Eu³⁺).