Solvent-Driven Switchable Structural Deformations in a Flexible Metal-Organic Framework with Pyrrolo-Pyrrole-Based Linker

A new flexible Zn-based metal-organic framework (IAM-9) containing a tetraarylpyrrolo[3,2-b]pyrrole (TAPP) dicarboxylate linker has been synthesized when using DEF as the solvent. Single-crystal-to-single-crystal structural transformation upon methanol exchange clearly demonstrates the dynamic nature of IAM-9, which is further confirmed by the powder X-ray diffraction studies and the gated adsorption isotherm for C₂H₂. Structural analysis suggests that the flexible Zn-carboxylate connection is primarily responsible for the observed structural changes. IAM-9 exhibits a solvent-dependent and size-selective flexibility and could readily convert between open and contracted phases upon adsorption or removal of small-sized solvent molecules. Our studies also show that the flexible structure of IAM-9 can selectively recognize DEF through the concurrent multiple interactions between adaptive host and DEF molecules. Owing to the π-expanded TAPP linker used, the photophysical properties of IAM-9 have also been studied. Compared with the organic linker, IAM-9 exhibits a considerably higher fluorescence quantum yield and larger two-photon absorption cross section.