Tuning Mesophase of Ammonium Amphiphile-Encapsulated Polyoxometalate Complexes through Changing Component Structure

A series of biphenyl-containing ammonium amphiphiles with two alkyl chains, N,N -di[10-[4-(4′-alkyloxybiphenyl)oxy]decyl]- N,N -dimethylammonium bromide (C n BphC 10 N, n = 6, 8, 10, 12), were designed and synthesized to cap the polyoxometalates (PMs), forming corresponding amphiphile-encapsulated complexes (PM-m/C n BphC 10 N). To understand the effect of organic and inorganic components on the mesomorphic behavior of hybrid materials, we examined the thermal properties of these complexes and their organic components as the comparison using differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction. The mesophase type of PM-1/C n BphC 10 N is independent of the variety of tail length of amphiphiles. However, different smectic phases, such as smectic A, smectic C, smectic B, and crystalline smectic phases, can be obtained by appropriate selection of the polyoxometalates (PM-2, PM-3, and PM-4) with different shape and surface charge density. The present results provide a direct correlation between liquid crystalline properties of the hybrid complex and the feature of inorganic PMs.