The flexibility of soft porous crystals, i.e., their ability to respond to external stimuli with structural changes, is one of the most fascinating features of metal-organic frameworks. In addition to breathing and swelling phenomena of flexible MOFs, negative gas adsorption and pressure amplification is one of the more recent discoveries in this field, initially observed in the cubic DUT-49 framework. In recent years the structural contraction was monitored by physisorption, X‑ray diffraction, NMR and EPR techniques, providing only limited information about the electronic structure of the ligand. In this work we designed a new ligand with a fluorescent core in the linker backbone and synthesized three new MOFs, isoreticular to DUT-49, denoted as DUT‑140(M) (M - Cu, Co, Zn) crystalizing in space group. DUT‑140(Cu) can be desolvated and is highly porous with an accessible apparent surface area of 4870 m2g-1 and a pore volume of 2.59 cm3g-1. Furthermore, it shows flexibility and NGA upon adsorption of subcritical gases. DUT-140(Zn), synthesized using post-synthetic metal exchange, could only be studied with guests in the pores. In addition to the investigation of the adsorption behavior of DUT-140(Cu) spectroscopic and computational methods were used to study the light absorption properties.
DUT-140 26052021 SI