Highly Luminescent Crystalline Sponge: Sensing Properties and Direct X-ray Visualization of the Substrates.

A phenomenon of crystalline sponge is represented by guest-dependent structural fluidity of the host polymeric lattice in highly crystalline sorbents, such as metal-organic frameworks, driven by multiple weak intermolecular interactions. Such induced fitting in MOFs is a valuable property in selective adsorption, guest determination by single-crystal XRD and in-situ structural analysis under external stimuli. In this work, a porous three-dimensional metal-organic framework [Eu 2 (DMF) 4 (ttdc) 3 ]·4.45DMF ( 1 DMF ; DMF = N , N -dimethylformamide, ttdc 2- = trans-thienothiophenedicarboxylate anion) was applied as a crystalline sponge bearing luminescent functionality to couple its sensing properties with direct structural determination of the adsorbed molecules. As a result, the paper discusses crystal structures and luminescent properties for the successfully obtained new adducts with the crystallographic formulae [Eu 2 (DMSO) 4 (ttdc) 3 ]·2.5DMSO·2.2H 2 O ( 1 DMSO ; DMSO = dimethylsulfoxide), [Eu 2 (DMF) 4 (ttdc) 3 ]·3phet ( 1 phet ; phet = phenylethanal) and [Eu 2 (DMF) 3.5 (cin) 0.5 (ttdc) 3 ]·1.64cin ( 1 cin ; cin = trans -cinnamaldehyde). As a result of inclusion of DMSO into 1 , a slight increase in the quantum yield and excited state phosphorescence lifetime was observed, while the adsorption of phet leads to a considerable (up to three times) decrease in the corresponding values. The incorporation of cinnamal results in a full quenching of QY, from 20% down to zero, and a more than order of magnitude diminishing of the excited state lifetime compared to the initial 1 DMF . The effective sensing of cinnamal was explained from the structural point of view by its direct coordination to the Eu 3+ emitter, as well as by multiple weak intermolecular interactions with ttdc antenna ligand, both capable of enhancing the non-radiative energy dissipation.