Tetrahydroxyhexanedioic Acid-Ornamented Phosphite-and-Bismuth-Bridging EuIII-Encapsulated Phospho(III)tungstate and Its Photochromic and Photoluminescence Switching Properties

Developing photoresponsive materials exhibiting both photochromic and photoluminescent switching properties presents a significant scientific challenge. Herein, a tetrahydroxyhexanedioic acid-ornamented phosphite-and-bismuth-bridging multi-EuIII encapsulated phospho­(III)­tungstate [H2N­(CH3)2]8Na6[Eu4W6Bi2O12(HPIIIO3)2(H2THHA)2(H2O)10]­[HPIII W9O33]4 · 50H2O (1, H6THHA = tetrahydroxyhexanedioic acid) was obtained, whose polyanion encompasses four trivacant Keggin-type [B-α-HPIIIW9O33]8– units and a complex heterometallic {[Eu4W6Bi2O12(HPIIIO3)2(H2THHA)2(H2O)10]}14+ cluster, wherein [HPIIIO3]2– anions and Bi3+ ions serve as bridging linkers, while the long-chain multidentate H2THHA4– ligands coordinate with W and Bi atoms. Intriguingly, 1 exhibits remarkable photochromic behavior upon UV irradiation, rapidly changing from colorless to blue within 180 s and reverting to its original colorless state within 5 h in the absence of irradiation, suggesting its potential as a fast-responsive photochromic material. Moreover, the photoluminescence of 1 can be reversibly modulated through photochromic activation, indicating its applicability as a molecular switch. Importantly, the reversible color change can be cycled at least ten times without significant degradation. Spectroscopic analyses including IR, XRD, XPS, EPR and Raman confirm that the photochromic behavior arises from the structural reduction of WVI centers to WV species. Furthermore, the 1-based photochromic film was fabricated and applied for erasable ink-free printing. This work highlights the effectiveness of integrating multicomponent systems in the design of polyoxometalates and broadens the scope of research on the photochromic properties of these materials.