Lamellar-Smectic Polyoxometalate Liquid Crystal Encapsulated by Branched Bola-Form Amphiphiles

The quaternary ammonium amphiphile A6 with carboxylic acid group was employed to encapsulate the europium-containing inorganic polyoxometalate Na-9[EuW10O36] through ionic self-assembly strategy. The resultant surfactant-encapsulated polyoxometalate complex A6Eu was characterized by FT-IR spectra, thermogravimetric analysis and elemental analysis in detail. The dimerization of the carboxylic acid groups through intermolecular hydrogen bonding gives rise to a branched bola-form structure of the organic moieties, which leads to a lateral attachement of the peripheral mesogen to the inorganic cluster. The thermotropic liquid crystalline properties of polyoxometalate complex were characterized by differential scanning calorimetry, polarized optical microscopy, and temperature-dependent X-ray diffraction. A6Eu exhibited novel lamellar-smectic mesophase in which the mesogen is organized parallel to the layer planes, while the amphiphile A6 alone was found to form simple smectic structures. The lateral attachment of the mesogen was demonstrated to have an important influence on the thermotropic organized structures of the complex. The luminescence of polyoxometalate is well retained in the liquid crystalline mesophase.

Automated summary

In this study, the quaternary ammonium amphiphile A6 was used to encapsulate the europium-containing inorganic polyoxometalate, resulting in a thermotropic liquid crystalline phase with unique structural and properties. The dimerization of carboxylic acid groups facilitated lateral attachment of the mesogens to the inorganic cluster, significantly influencing the thermotropic organized structures of the complex. The luminescence of the polyoxometalate was well retained in the liquid crystalline mesophase.