Self-assembly of benzimidazole-containing rodcoil molecules

Abstract

This thesis deals with self-assembly of benzimidazole-containing rodcoil molecules. Benzimidazole-containing rodcoil molecules N12 and M12 were synthesized as miniature rodcoil block copolymers. Self-assembly behavior of N12 in DMSO solution was detected by $^1H$ NMR spectrum. Self-assembled structure was characterized using SEM and XRD. SEM image showed loose network composed of fibers with irregular shapes. XRD analysis suggested lamellar structure with layer spacing of 3.709 nm, which is composed of two intercalated molecules. The driving force of self-assembly was thought to π-π interaction of benzimidazole and hydrogen bonding between NH of benzimidazole ring and O atom of nitro group. After sonication, deformation of self-assembled structure was observed from NMR spectrum. Self-assembly of M12 in DMSO solution was detected by dynamic light scattering study. Self-assembled structure was characterized using SEM, TEM and XRD. SEM and TEM images showed that sheetlike aggregates were formed. From the XRD pattern, the structure of aggregates was proposed as lamellar structure with layer spacing of 2.307 nm, without intercalating. The structure difference from N12 might stem from the presence of bulky $CF_3$ group. After sonication, SEM and TEM images showed a new fibrous structure was formed. Electron diffraction pattern of a single fiber indicated π-π stacking occurred perpendicular to the long axis. The mechanism of structure transformation was understood in terms of the disturbance of hydrogen bonding and increase of hydrophobic interaction.