Formation of Highly Luminescent Supramolecular Architectures Possessing Columnar Order from Octupolar Oxadiazole Derivatives: Hierarchical Self‐Assembly from Nanospheres to Fibrous Gels

Abstract

The synthesis and study of the liquid crystalline, photophysical, and aggregation behavior of novel octupolar oxadiazole derivatives are reported. These molecules formed columnar mesophases at elevated temperatures which transformed into a glassy state at ambient temperatures wherein the columnar order was retained. Their spontaneous concentration dependent hierarchical self‐assembly from spheres to fibrous gels has been investigated using TEM, SEM, and XRD. Retention of the hexagonal columnar (Colh) order was also observed in the fibrous aggregates. Concentration dependent luminescence spectral studies indicated that the change in morphology from spheres to fibrous aggregates was associated with a shift in chromophore packing from predominantly H‐type to J‐type aggregates. Time resolved anisotropic investigations revealed that the columnar stacking of molecules in the aggregated state provided a pathway for excitation energy migration to the lower energy J‐traps.

Controlled Sol–Gel and Diversiform Nanostructure Transitions by Photoresponsive Molecular Switching of Tetraphenylethene- and Azobenzene-Functionalized Organogelators

“…The 2D ROESY spectrum of [2]rotaxane R1-b shows a spatial correlation between the proximity proton signals of tbutylcalix [4]arene macrocycle (H 8 −H 13 ) and those associated with H a , H b , and H c of the 3,5-bistrifluoromethylbenzene stopper nearby the urea station (see Figure S47, SI), which clearly supports that this dynamic nature is induced by the external stimuli.…”

“…Considering the interest of acid/base and photoresponsive morphological transformation in organogels, we synthesized the target [2]rotaxanes and axles using a multicomponent system containing azobenzene (photoactive), urea (binding site for the macrocycle), and a terminal bulky TPE. Stimuli-responsive [2] synthesized first, which consist of a crown ether macrocycle incorporating a t-butylcalix [4]arene unit and a thread bearing two distinguishable recognition stations (secondary ammonium and urea), similar to that developed by Beer and coworkers for lactide ring-opening polymerization. 52 It is worth noting that our axles (T1 and T1-b) involve multi-noncovalent interactions to self-assemble into various 3D gelation networks.…”

“…To prepare the target [2]rotaxane R1, we took the threading-followed-bystoppering approach (Schemes 2 and S5, SI). To start with, the TPE alkyne derivative TPE-B, which incorporates a secondary ammonium station, was treated with t-butylcalix [4]arene macrocycle S8 to form a pseudorotaxane in dry dichloromethane. Subsequently, the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction was used to form the triazole ring with the azobenzene-functionalized azide compound Azo-A, followed by counterion exchange that afforded the target [2]rotaxane R1 in 20% yield.…”

“…Deprotonation of the resulting secondary ammonium ion with NaOH aq yielded the desired [2]rotaxane R1-b in 80%, as shown in Scheme S5. In the absence of t-butylcalix [4]arene macrocycle S8, axle T1 can be synthesized similarly using the CuAAC reaction between TPE-B and Azo-A, which gave axle T1 in 37% yield. Axle T1 can then be treated with NaOH aq to yield axle T1-b in 72% yield (Scheme S4).…”

Simulation Model for Hierarchical Self-Assembly of Soft Disklike Particles

“…When the solvent condition becomes bad (i.e., the repulsion strength α 12 R is equal to or larger than the critical repulsion parameter for phase separation, which is about α 12 R = 270 for the concentration of the disklike particles ϕ = 5%), phase separation take places, and eventually brings the threads to approach to each other, an intermediate phase characterized by clustering between nearby threads is observed, as shown in Figure c. When the solvent quality further decreases, the disklike particles can self-assemble into hexagonal bundle structures (the structure is very similar to the one observed in experiments), , as can be clearly seen in Figure d and e. The bundle thickness is approximately up to 20−30 threads. It should be noted that the bundle is flexible in comparison with that formed by semiflexible filamentous biopolymers, − since it is hierarchically formed by soft disklike particles in our case.…”