Affiliation:
1. Institute of Inorganic Chemistry Christian‐Albrechts‐University Kiel Max‐Eyth‐Street. 2 24118 Kiel Germany
2. Max‐Planck‐Institute for Solid State Research Heisenbergstr. 1 70596 Stuttgart Germany
3. Kiel Nano, Surface and Interface Science KiNSIS Christian‐Albrechts‐University Kiel Christian‐Albrechts‐Platz 4 24118 Kiel Germany
4. Inorganic Photoactive Materials Heinrich Heine University Düsseldorf Universitätsstr. 1 40225 Düsseldorf Germany
Abstract
AbstractThe new microporous metal organic framework [La2(H2O)5(H2TPPE)]·3H2O (CAU‐54), is obtained in a hydrothermal reaction of the linker 1,1,2,2‐tetrakis(4′‐phosphonophenyl)ethylene (H8TPPE) and La3+ ions. The extensive characterization including temperature‐dependent crystal structures and spectroscopic properties allowed to understand the unique, multi‐responsive material properties. CAU‐54 exhibits rarely observed reversible photochromism as well as turn‐on photoluminescence by various external chemical or physical stimuli including change of pressure, solvent exchange, and temperature variation. These properties can be unequivocally assigned to the presence of tetraphenylethylene (TPE) moieties of the linker molecules within the MOF, i.e., the ordered spatial arrangement of the linker molecules, the presence of accessible pores as well as the coordination flexibility of the phosphonate groups and the rotational freedom of the linker. By temperature‐dependent steady‐state and time‐resolved luminescence studies, it is shown that this compound exhibits a) blue fluorescence that becomes effectively quenched at room temperature, b) green efficient luminescence with thermal stability up to 400 K, and c) red phosphorescence correlated to the observed photochromism. In addition, CAU‐54 shows unusual thermal expansion properties as shown by temperature‐dependent powder X‐ray diffraction measurements with identified transition points that correlate with the observed temperature‐dependent changes in the photoluminescence.