Tunable columnar organization by twisted stacking of end-capped aromatic rods

Abstract

The dumbbell-shaped aromatic amphiphilic molecules consisting of hexa-p-phenylene-conjugated carbazole moieties on both ends as a rigid rod segment and oligoether chains with different cross-sections (i.e., linear branch (1), dibranch (2), and tetrabranch (3)) attached to a carbazole as flexible chains were synthesized and their self-assembling behavior investigated using DSC, X-ray scatterings, and TEM. These dumbbell-shaped molecules based on an end-capped rod segment self-assemble into a tunable 21) supramolecular structure depending on cross-sectional area of the flexible dendritic chain. With increasing cross-sectional area of the flexible chains, the 21) structure changes from rectangular to oblique columnar structures with a successive increase in the lattice constant a relative to b. This structural change is also accompanied by increasing temperature as in the case of 2 and 3. The molecular rearrangements at the phase transitions were proposed to undergo a scissoring motion of the two adjacent rods along the column axis. Considering that all other self-assembling systems based on rigid rod segments have a strong tendency to be aligned parallel to each other, the remarkable feature of the end-capped rod segment investigated in this study is the ability to control 2D supramolecular structure through a unique scissoring motion between the two adjacent stacked rods