Synthesis And Liquid Crystalline Properties Of Chiral Polyoxometalates Supramolecular Complexes

Polyoxometalates?POMs?,as a sort of nanoscaled inorganic single-molecule clusters,possess rich chemical composition,adjustable surface charge and stable topological structure,which exhibiting broad applications in materials,catalysis,biomedicine and other fields.The applications of chiral POM in asymmetric catalysis,chiral recognition and so on could be further expanded by introducing chiral moieties into POMs.However,the POMs with highly symmetrical structure will easily racemize in solution and lose optical activities even if they are chiral.These factors greatly limited the functional applications of POMs in chiral field.POMs exhibited liquid crystalline properties with different mesophases.However,the reports about liquid crystals based on POMs mainly focused on the achiral liquid crystals so far,there are few reports on chiral liquid crystals.How to easily design and develop chiral liquid crystalline materials based on POMs is a promising exploration direction in POMs chemistry.Based on the above considerations,the quaternary ammoniums amphiphile containing cholesterol chiral groups was used to encapsulate the three non-chiral POMs[SiW₁₂O₄₀]^4-,[PW₁₁O₃₉]^7-and[BW₁₁O₃₉]^9-through electrostatic interactions.The structures and compositions of the complexes were characterized by elemental analysis,infrared spectroscopy and thermogravimetric analysis.The results showed that organic cations and inorganic anions could form chiral supramolecular complexes of POMs by electrostatic interactions.The optical activities of the complexes were characterized by UV and CD spectrum,which showed that chiral organic cations could induce supramolecular complexes to exhibit chiral signals by electrostatic interactions.The thermotropic liquid crystalline properties of the complexes were analyzed by differential scanning calorimetry,polarized optical microscopy,variable temperature X-ray diffraction and variable temperature infrared spectrum.The results showed that the complexes exhibited liquid crystalline properties with chiral SmA phase with wide temperature range.The above results confirmed that chiral liquid crystalline materials based on POMs were constructed.It is a simple and effective method to prepare chiral supramolecular liquid crystal materials by electrostatically encapsulation of the non-chiral inorganic anionic clusters with chiral organic cationic.This method will provide novel ideas for the construction of chiral supramolecular liquid crystal materials.Supramolecular chiral materials with functional properties of nanoparticles and liquid crystalline properties of organic components will have potential applications in the fields of asymmetric catalysis,chiral recognition and circularly polarized luminescence.