Multinuclear Lanthanide-Implanted Tetrameric Dawson-Type Phosphotungstates with Switchable Luminescence Behaviors Induced by Fast Photochromism

Abstract

A series of benzoate-decorated lanthanide (Ln)-containing tetrameric Dawson-type phosphotungstates [N(CH₃)₄]₆H₂₀[{(P₂W₁₇O₆₁)Ln(H₂O)₃Ln(C₆H₅COO)(H₂O)₆]}{[(P₂W₁₇O₆₁)Ln(H₂O)₃}]₂Cl₂·98H₂O [Ln = Sm (<b>1</b>), Eu (<b>2</b>), and Gd (<b>3</b>)] were made using a facile one-step assembly strategy and characterized by several techniques. Notably, the Ln-containing tetrameric Dawson-type polyoxoanions [{(P₂W₁₇O₆₁)Ln(H₂O)₃Ln(C₆H₅COO)(H₂O)₆]}{[(P₂W₁₇O₆₁)Ln(H₂O)₃}]₂^24- are all established by four monolacunary Dawson-type [P₂W₁₇O₆₁]^10- segments, encapsulating a Ln³⁺ ion with two benzoates coordinating to the Ln³⁺ ions. <b>1</b>-<b>3</b> exhibit reversible photochromism, which can change from intrinsic white to blue for 6 min upon UV irradiation, and their colors gradually recover for 30 h in the dark. The solid-state photoluminescence spectra of <b>1</b> and <b>2</b> display characteristic emissions of Ln components based on 4f-4f transitions. Time-resolved emission spectra of <b>1</b> and <b>2</b> were also measured to authenticate the energy transfer from the phosphotungstate and organic chromophores to Eu³⁺. In particular, <b>1</b> shows an effectively switchable luminescence behavior induced by its fast photochromism.