Color tuning and white light emission by codoping in isostructural homochiral lanthanide metal–organic frameworks

Abstract

Four lanthanide-based homochiral metal–organic frameworks (Ln-HMOFs), {[Ln₂(HL)₂(H₂O)₄]·2Cl·5H₂O}_n [Ln = Gd (1), Eu (2), Tb (3) and Dy (4)], have been synthesized through solvothermal reactions of chiral ligand (S)-5-(((1-carboxyethyl)amino)methyl)isophthalic acid (H₃L) with corresponding LnCl₃·6H₂O. They are binodal (3,6)-connected frameworks with kgd nets based on binuclear cluster units and zwitterionic (HL)²⁻ linkers. Considering the isostructuralism of these Ln-HMOFs as well as the blue emission of compound 1 and the strong typical Eu³⁺ and Tb³⁺ emissions of compounds 2 and 3, single-phase mixed-lanthanide HMOFs have been prepared by doping of Ln³⁺ into the Ln-HMOFs to modulate light-emitting color. Interestingly, the bimetallic doped Eu/Tb-HMOFs [(Eu_xTb_1−x)₂(HL)₂(H₂O)₄]·2Cl·5H₂O display a fluent change of light-emitting color among green, yellow, orange, orange-red, and red by adjusting the doping concentration of Eu³⁺ ions into the Tb-HMOF. Very importantly, the trimetallic doped Eu/Gd/Tb-HMOF [(Eu_0.1388Gd_0.6108Tb_0.2504)₂(HL)₂(H₂O)₄]·2Cl·5H₂O emits white light upon excitation at 355 nm, whose emission can also be switched between different colors when excited with different ultraviolet light. Furthermore, the fluorescence response of Tb-HMOF to various usual metal ions, and especially fluorescent sensing behaviours to Fe³⁺, Cr³⁺ and Al³⁺ have been preliminarily investigated.