Supramolecular Self-Assembly in a Disk-Cube Dyad Molecule Based on Triphenylene and Polyhedral Oligomeric Silsesquioxane (POSS)

An asymmetric disk-cube dyad molecule was synthesized by covalently attaching a 2-hydroxy-3,6,7,10,11-pentakis(pentyloxy)triphenylene (P5T−OH) discotic molecule to a cubic polyhedral oligomeric silsesquioxane (POSS) molecule via a spacer. The sample was denoted as P5T−POSS. 1 H and 13 C nuclear magnetic resonance and size-exclusion chromatography were used to verify both its chemical structure and purity. On the basis of differential scanning calorimetry, two-dimensional (2D) X-ray diffraction (XRD), and transmission electron microscopy (TEM) analyses, we observed nanophase separation between the liquid crystalline P5T and crystalline POSS lamellae in the neat P5T−POSS and a miscible 1:1 mol/mol blend of P5T−POSS and POSS (denoted as 1:1 P5T−POSS:POSS). The melting temperatures of POSS crystals in P5T−POSS and 1:1 P5T−POSS:POSS were 62 and 66 °C, respectively. The isotropization temperature ( T i ) of liquid crystalline P5T in P5T−POSS superposed with the POSS crystal melting at 66 °C, whereas it was at −5 °C in 1:1 P5T−POSS:POSS. The cubic POSS molecules in a planar hexagonal lattice stacked into an ABCA four-layer lamellar crystal, which had the same rhombohedral crystal structure (space group R 3̄ m ) as pure POSS crystals. Computer-simulated XRD for a lamellar model consisting of ABCA four-layer spheres and an amorphous lamella demonstrated that major crystal reflections, such as (101̄1), (112̄0), (101̄2), and overlapped (112̄3)/(303̄0), were still observable with the same d -spacing as those in pure POSS crystals. The discotic P5T molecules formed a bilayer liquid crystalline lamella between POSS lamellar crystals in P5T−POSS, whereas they interdigitated in the 1:1 P5T−POSS:POSS blend. Although no reflections related to columnar mesophases were observed in the 2D XRD patterns of P5T−POSS, the P5T discotic molecules were found to orient parallel to the lamellar normal in the confined space, reminiscent of a homeotropic nematic discotic structure.