Topology Controlled Supramolecular Self-Assembly of Octa Triphenylene-Substituted Polyhedral Oligomeric Silsesquioxane Hybrid Supermolecules

Abstract

A series of liquid crystalline star supermolecules with polyhedral oligomeric silsesquioxane (POSS) as the central scaffold and eight triphenylenes (Tp) as the peripheral arms were synthesized via amidization reactions. The supermolecules were denoted as POSS(Tp)(8). Six POSS(Tp)(8) samples were prepared with two alkyl chain lengths in the Tp (C(5) and C(12)) and three spacer lengths (C(2), C(6), and C(10)) between the POSS core and the Tp arms. Three samples with C(5)-Tp were amorphous because of too short alkyl chains in the Tp, while the other three samples with C(12)-Tp self-assembled into hierarchical liquid crystalline mesophases, as studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). When the spacer length was C(2), a column-within-column super hexagonal columnar phase was observed, because the POSS core and the Tp arms were intimately coupled together. With increasing the spacer length to C(6) and C(10), respectively, the POSS core and Tp arms became gradually decoupled. Alternating POSS-Tp lamellar morphology with a rectangular columnar symmetry (by XRD) was observed by TEM for the POSS(Tp)(8) sample with a C(6)-spacer. For the POSS(Tp)(8) sample with a C(10)-spacer, an oblique columnar phase was determined by XRD, and inverted columnar morphology with four Tp columns forming a super column within the POSS/alkyl chain matrix was observed by TEM. This study suggested that molecular topology played an important role in the supramolecular self-assembly of star-shaped POSS(Tp)(8) supermolecules.