Rare earth inorganic-organic hybrid compounds based on Keggin-type polyoxometalate {SiW12} with fast-responsive photochromism and switchable luminescence properties

Four rare earth inorganic -organic hybrid compounds based on Keggin-type polyoxometalate {SiW12} with general formula [{RE(DMF)4(H2O)4RE(DMF)6}2{SiW12O40}3] (RE = La(1), Pr(2), Sm(3), Eu(4), DMF = N,N-dimethylformamide) were synthesized by the conventional solution method. Structure analyses indicate that four compounds are isostructural and are all built from three [SiW12O40]4- polyoxoanions and DMF ligands linked by RE3 thorn . Compounds 1-4 are extremely sensitive to UV light and present excellent photochromic properties, in which the coloring and fading time of samples are both no more than 2 min, and the reversible coloring -fading process can be repeated for at least 10 cycles with little fatigue, suggesting that compounds 1-4 can be a series of fast -responsive and durable photochromic materials. Moreover, the solid-state photoluminescence spectra of compounds 3(Sm) and 4(Eu) display strong characteristic emissions of rare earth ions based on f -f transitions. Meanwhile, compound 4(Eu) has a longer fluorescence lifetime up to 566.74 ms. Notably, compounds 3(Sm) and 4(Eu) exhibit the switchable luminescence behavior induced by photochromism, which allows them to be used as potential molecular switches. (c) 2022 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.