Spontaneous Organization of Supramolecular Rod-Bundles into a Body-Centered Tetragonal Assembly in Coil−Rod−Coil Molecules

Abstract

The synthesis and characterization of coil-rod-coil molecules of 4, 4′-bis[4-methyloxypoly-(propyleneoxy)propyloxy-4′-biphenyloxymethyl]biphenyl with a poly(propylene oxide) coil of 3 (7), 6 (8), 9 (9), 13 (10), 17 (11), and 22 (12) propylene oxide units are described. These molecules self-assemble into ordered structures that differ significantly on variation of the length of poly(propylene oxide) coil. Coilrod-coil molecule 7 self-organizes into lamellar crystalline and bicontinuous cubic liquid crystalline assemblies, while 8 shows a hexagonal columnar liquid crystalline assembly. Remarkably, increasing the length of coil induces discrete supramolecular aggregates that self-assemble into a birefringent 3-D superlattice. The molecules 9 and 10 assemble into discrete supramolecular aggregates that spontaneously organize into a novel 3-D tetragonal lattice with a body-centered symmetry in the crystalline and melt states. Further increasing the length of coil as in the case of 11 and 12 induces only a body-centered tetragonal crystalline phase, while the liquid crystalline phase in these molecules is suppressed. X-ray diffraction experiments and density measurements showed that the aggregation of these molecules into a discrete supramolecular structure gives rise to aromatic rod bundles with hockey puck-like cylindrical shape encapsulated by phase-separated coil segments which results in the formation of oblate aggregates. This nonspherical oblate shape is believed to be responsible for the formation of a body-centered tetragonal phase. These results demonstrate that supramolecular structures, from 1-D lamellar to 3-D tetragonal superlattices, formed by the self-assembling process of molecular rods can be controlled in a systematic and predictive way by simple variation of the length of grafted coils.

Functional Liquid‐Crystalline Assemblies: Self‐Organized Soft Materials

“…Lee and co-workers synthesized coil-rod-coil and rod-coil molecules consisting of aromatic rigid parts and poly(propylene oxide) coils. [178][179][180] The length of the coil part significantly affects the ordered structures of molecules. Coil- Figure 14.…”

Self-Assembly of Poly(diethylhexyloxy-p-phenylenevinylene)-b- poly(4-vinylpyridine) Rod−Coil Block Copolymer Systems

“…These structures have already been observed in various rod-coil block copolymers: Stupp et al reported formation of lamellar and hexagonal phase-separated domains for various rod to coil volume fractions in monodisperse rod-coil diblock copolymers, 28 whereas lamellar and bicontinuous liquid crystalline assemblies as well as hexagonal columnar phase are observed in rod-coil-rod triblock copolymers. 29 The emphasis of the present work is placed on the study of the synthesis, design, and self-assembly mechanisms of PPV-b-P4VP block copolymers, with particular accent on morphologies exhibiting continuous domains, such as hexagonal and lamellar, of possible use as templates in organic photovoltaic devices.…”

Nanoscale Organization of Conjugated Rods in Rod-Coil Molecules

“…In a more recent publication, rod±coil ABA triblock molecules based on poly(propylene oxide) as the coil segment were proved to self-assemble into discrete rod bundles that organize into a 3D tetragonal structure. [8] Our approach to controlling supramolecular architecture can be extended to rod±coil systems based on a conjugated rod, which create a novel class of self-assembling materials with unique optical and electronic properties. As a result of great interest in the optically and electronically active properties of highly conjugated and stiff rod-like molecules, a variety of oligomers and polymers have been synthesized to establish the molecular structure±property relationship.…”

“…These were initially crystallized onto a gold-coated glass slide from colloidal solution. [8,9] The resulting metallic mesh reflects the order of the self-assembled template, allowing convenient control of the pore diameters and local crystalline order. Measurement of the total charge passed allows accurate deposition of the required metal thickness, after which the template can be dissolved in toluene.…”