Lanthanide functionalized hybrid materials of polyoxometallate based metal–organic frameworks for multi-color luminescence

Lanthanide functionalized hybrids of polyoxometallate based MOF Ln³⁺⊂COK-15 are prepared and display multi-color light, together with a white luminescence (x = 0.3845, y = 0.303) by tuning an appropriate amount of Eu³⁺ and a suitable excitation wavelength.

Reversible proton-switchable fluorescence controlled by conjugation effect in an organically-functionalized polyoxometalate

A novel monosubstituted organoimido hexamolybdate containing 6-nitroquinoline moiety has been successfully synthesized. This organically-functionalized polyoxometalate exhibits proton-induced switchable fluorescence property in aqueous acetonitrile solution at room temperature. Experimental and theoretical investigations of this reversible “on” and “off” switching mechanism have been carried out, and it is found that the protonation and deprotonation at the heterocyclic nitrogen atom within quinoline fragment leads to the breaking and reformation of the conjugation through strong d-π interaction between the hexamolybdate anionic cluster and the quinoline moiety, resulting in “on” and “off” luminescence signal.

Multi-component assembly and luminescence tuning of lanthanide hybrids through the inside–outside double modification of zeolite A/L

A novel inside–outside double modification path is used to functionalize ZA/L to construct multi-component hybrids presenting multi-color luminescence.

Fabrication and photoluminescence of hybrid organized molecular films of a series of gemini amphiphiles and europium(III)-containing polyoxometalate

Organic/inorganic hybrid monolayers, consisting of an oval decatungstoeuropate (EuW10) with photoluminescence and a series of gemini-type amphiphiles with various lengths of the flexible hydrophobic spacers, were formed through electrostatic interaction at the air/water interface. The ultrathin hybrid multilayer films could be fabricated through the horizontal transfer of the monolayers onto the solid substrates. The characteristic absorption band of EuW10 in the UV spectra of the hybrid films showed a slight red shift in comparison with that in solution, indicating the ordered arrangement of EuW10 in the hybrid films. FT-IR spectra of the hybrid films presented characteristic bands of EuW10, indicating that the structure of the cluster was kept in the films. X-ray diffraction measurements of the films revealed that the well-defined layer structures were formed in these multilayer films and the EuW10 cluster ions were orientated with their short axis parallel to the film surface. Typical photoluminescence of the 5D0 --> 7F2 and 5D0 --> 7F1 transitions of EuW10 was observed in the hybrid films. Interestingly, the relative intensity of the two emission bands varied with the spacer length of the gemini amphiphiles in the films. A size matching between EuW10 and the gemini amphiphile with a hexamethylene spacer was observed, which showed the lowest ratio of the emission intensity of 5D0 --> 7F2 to that of 5D0 --> 7F1. Circular nanoparticles were observed in the AFM images for all these hybrid films. In addition, the size of the formed nanoparticles showed a dependence on the spacer length.

Layer-by-Layer Assembly of Polyoxometalates into Microcapsules

The polyoxometalate (POM) chemistry world has been experiencing an unparalleled development of rapid synthesis of new compounds and slow development of POM-based functional materials and devices. Meanwhile, researchers in the microcapsule world, encouraged by the introduction of the layer-by-layer method, are pursuing good components for constructing functional capsule devices. Here, in view of the versatile properties that POM-based microcapsules may possess, various types of POM-polyelectrolyte composite microcapsules were constructed using the layer-by-layer method. Microscopy reveals that polyoxometalates form nanoparticles on the shell in the presence of cationic polyelectrolytes. These nanoparticles connected with polyelectrolytes constitute the shell and support the microcapsule from collapse after drying, and this is an interesting characteristic different from those of common composite and polyelectrolyte capsules. Fourier transform infrared (FTIR), UV-vis absorption, and X-ray photoelectron spectroscopy (XPS) were used to examine the properties of the POMs in the microcapsules. The obtained microcapsules exhibit higher thermal stability than polyelectrolyte microcapsules. Furthermore, the functions of POMs were maintained when they were assembled into microcapsules. It is proved that microcapsules bearing POMs with redox activity can provide a reduction environment, which can lead to the realization of in situ synthesis of materials, and that microcapsules with photoluminescent POMs as a component can also have a photoluminescent property, providing a way to develop functional capsule devices. This work may provide an opportunity to enrich both the polyoxometalate chemistry and the capsule field.