Interpenetration-Enabled Photochromism and Fluorescence Photomodulation in a Metal-Organic Framework with the Thiazolothiazole Extended Viologen Fluorophore.

A novel metal-organic framework (MOF), formulated as [Cd2(TTVTC)Cl2(H2O)3]·2H2O (1), was synthesized from a tetracarboxylate ligand ([TTVTC]2-) functionalized with the thiazolothiazole extended viologen (TTV2+) fluorophore. The MOF features three-dimensional (10,3)-d frameworks with 6-fold interpenetration. The MOF exhibits reversible photochromism, due to photoinduced electron transfer from carboxylate to TTV2+. The photoactivity benefits from the electron donor-acceptor contacts enabled by mutual interpenetration of the frameworks. This is the first demonstration of photochromism in TTV2+ derivatives. In addition, the fluorescence arising from the TTV2+ fluorophore can be reversibly modulated during the photochromic process. The work demonstrates the great potential of extended viologen based ligands in the construction of MOFs with dual photomodulable optical properties, which could find future applications in photoelectronics.