Macroscopically oriented hierarchical structure of the amphiphilic tetrathiafulvalene molecule

Abstract

Since the physical properties of electronic and biological molecules strongly depend on the nature of molecular self-assembly and organization, it is essential to control their molecular packing structure and morphology on the different length scales. In this aspect, a programmed amphiphilic tetrathiafulvalene (TTF) molecule (abbreviated as amph-7TTF14) was newly designed and synthesized. Differential scanning calorimetry (DSC) combined with one-dimensional (1D) wide angle X-ray diffraction (WAXD) techniques revealed that a highly ordered crystalline phase emerged below the isotropic phase. From the 2D WAXD pattern of the macroscopically oriented amph-7TTF14 film, the crystal structure was identified to be a monoclinic unit cell. The face-to-face π–π interaction between TTF groups and the nanophase separation between rigid TTF groups and flexible hydrophobic alkyl and hydrophilic tri(ethylene oxide) tails were the main driving forces for the self-assembly of amph-7TTF14. The morphological observations using transmission electron microscopy (TEM), atomic force microscopy (AFM), and polarized optical microscopy (POM) indicated that the amph-7TTF14 formed not only flat ribbons but also scrolls and helixes, in which the ribbons further aggregated to create the fibrous hierarchical structures. Based on the experimental results and careful analyses, it was realized that the scrolls and helices were induced by the unbalanced surface stresses generated during the crystallization process. When the macroscopically oriented fibrous hierarchical structure is properly applied to the electrooptical and bio-mimetic devices, the targeted physical properties may be significantly improved and tuned for the specific practical applications.