Fabrication of Semiconducting Nanoribbons with Tunable Length and Width via Crystallization-Driven Self-Assembly of a Homopolymer Prepared by Cyclopolymerization Using Grubbs Catalyst

Well-Defined Homopolymer Nanoparticles with Uniaxial Molecular Orientation by Synchronized Polymerization and Self-Assembly

Synthesizing anisotropic polymeric nanoparticles (NPs) with well-defined shapes, dimensions, and molecular orientations is a very challenging task. Herein, we report the synthesis of surprisingly highly uniform shape-anisotropic polymer NPs with uniaxial internal molecular orientation. Keys to our method are synchronized polymerization and self-assembly (SPSA), which can even be realized by regular dispersion polymerization. This is demonstrated using a monomer containing a rigid 4-nitroazobenzene (NAB) side group. The short nucleation period, the completion of microphase separation before molecular motion is frozen, and sufficient low particle/solvent interfacial tension are shown to be the origins of the highly uniform dimensions, single liquid crystal domains, and well-defined anisotropic shape of particles. The liquid crystallization ability of the polymers, control of molecular weight distribution, and the polymerization kinetics are identified as three key factors controlling the NP formation. The uniformity of these NPs facilitates their SA formation into colloidal crystals. The particles exhibit optically anisotropic properties depending on orientations and, in particular, show intriguing photoswitchable LC-glass (order-disorder) transition, which can be used for the detection of ultraviolet (UV) light and allows the fabrication of photoreversible colloidal films.

Independent Control of the Width and Length of Semiconducting 2D Nanorectangles via Accelerated Living Crystallization-Driven Self-Assembly

Self-assembly of conjugated polymers offers a powerful method to prepare semiconducting two-dimensional (2D) nanosheets for optoelectronic applications. However, due to the typical biaxial growth behavior of the polymer self-assembly, independent control of the width and length of 2D sheets has been challenging. Herein, we present a greatly accelerated crystallization-driven self-assembly (CDSA) system of polyacetylene-based conjugated polymer to produce 2D semiconducting nanorectangles with precisely controllable dimensions. In detail, rectangular 2D seeds with tunable widths of 0.2-1.3 μm were produced by changing the cosolvent% and grown in the length direction by uniaxial living CDSA up to 11.8 μm. The growth rate was effectively enhanced by tuning the cosolvent%, seed concentration, and temperature, achieving up to 27-fold increase. Additionally, systematic kinetic investigation yielded empirical rate equations, elucidating the relationship between growth rate constant, cosolvent%, seed concentration, and seed width. Finally, the living CDSA allowed us to prepare penta-block comicelles with tunable width, length, and height.

Uniform Colloidal Polymer Rods by Stabilizer-Assisted Liquid-Crystallization-Driven Self-Assembly

The synthesis of anisotropic colloidal building blocks is essential for their self-assembly into hierarchical materials. Here, a highly efficient stabilizer-assisted liquid-crystallization-driven self-assembly (SA-LCDSA) strategy was developed to achieve monodisperse colloidal polymer rods. This strategy does not require the use of block copolymers, but only homopolymers or random copolymers. The resulting rods have tunable size and aspect ratios, as well as well-defined columnar liquid crystal structures. The integrated triphenylene units enable the rods to exhibit unusual photo-induced fluorescence enhancement and accompanying irradiation memory effect, which, as demonstrated, are attractive for information encryption/decryption of paper documents. In particular, unwanted document decryption during delivery can be examined by fluorescence kinetics. This SA-LCDSA-based approach can be extended to synthesize other functional particles with desired π-molecular units.

Supramolecular Polymer Polymorphism: Spontaneous Helix-Helicoid Transition through Dislocation of Hydrogen-Bonded π-Rosettes

Polymorphism, a phenomenon whereby disparate self-assembled products can be formed from identical molecules, has incited interest in the field of supramolecular polymers. Conventionally, the monomers that constitute supramolecular polymers are engineered to facilitate one-dimensional aggregation and, consequently, their polymorphism surfaces primarily when the states of assembly differ significantly. This engenders polymorphs of divergent dimensionalities such as one- and two-dimensional aggregates. Notwithstanding, realizing supramolecular polymer polymorphism, wherein polymorphs maintain one-dimensional aggregation, persists as a daunting challenge. In this work, we expound upon the manifestation of two supramolecular polymer polymorphs formed from a large discotic supramolecular monomer (rosette), which consists of six hydrogen-bonded molecules with an extended π-conjugated core. These polymorphs are generated in mixtures of chloroform and methylcyclohexane, attributable to distinctly different disc stacking arrangements. The face-to-face (minimal displacement) and offset (large displacement) stacking arrangements can be predicated on their distinctive photophysical properties. The face-to-face stacking results in a twisted helix structure. Conversely, the offset stacking induces inherent curvature in the supramolecular fiber, thereby culminating in a hollow helical coil (helicoid). While both polymorphs exhibit bistability in nonpolar solvent compositions, the face-to-face stacking attains stability purely in a kinetic sense within a polar solvent composition and undergoes conversion into offset stacking through a dislocation of stacked rosettes. This occurs without the dissociation and nucleation of monomers, leading to unprecedented helicoidal folding of supramolecular polymers. Our findings augment our understanding of supramolecular polymer polymorphism, but they also highlight a distinctive method for achieving helicoidal folding in supramolecular polymers.

Dopant-Stabilized Assembly of Poly(3-hexylthiophene)

Polymer self-assembly is a powerful approach for forming nanostructures for solution-phase applications. However, polymer semiconductor assembly has primarily been driven by solvent interactions. Here, we report poly(3-hexythiophene) homopolymer assembly driven and stabilized by oxidative doping with iron (III) p-toluenesulfonate in benzonitrile. By this improved method, dopant mol % and addition temperature determine the size and morphology of oxidized polymer nanostructures. The dopant counterion provides colloidal stability in a process of dopant-stabilized assembly (DSA). Each variable governing polymer assembly is systematically varied, revealing general principles of oxidized nanostructure assembly and allowing the polymer planarity, optical absorption, and doping level to be modulated. Oxidized nanostructure heights, lengths, and widths are shown to depend on these properties, which we hypothesize is due to competing nanostructure formation and oxidation mechanisms that are governed by the polymer conformation upon doping. Finally, we demonstrate that the nanoparticle oxidative doping level can be tuned post-formation through sequential dopant addition. By revealing the fundamental processes underlying DSA, this work provides a powerful toolkit to control the assembly and optoelectronic properties of oxidatively doped nanostructures in solution.