Selective Separation of Lithium Chloride by Organogels Containing Strapped Calix[4]pyrroles.

Reported herein are two functionalized crown ether strapped calix[4]pyrroles, H1 and H2. As inferred from competitive salt binding experiments carried out in nitrobenzene-d5 and acetonitrile-d3, these hosts capture LiCl selectively over four other test salts, viz. NaCl, KCl, MgCl2, and CaCl2. Support for the selectivity came from density functional theory (DFT) calculations carried out in a solvent continuum. These theoretical analyses revealed a higher innate affinity for LiCl in the case of H1, but a greater selectivity relative to NaCl in the case of H2, recapitulating that observed experimentally. Receptors H1 and H2 were outfitted with methacrylate handles and subject to copolymerization with acrylate monomers and cross-linkers to yield gels, G1 and G2, respectively. These two gels were found to adsorb lithium chloride preferentially from an acetonitrile solution containing a mixture of LiCl, NaCl, KCl, MgCl2, and CaCl2 and then release the lithium chloride in methanol. The gels could then be recycled for reuse in the selective adsorption of LiCl. As such, the present study highlights the use of solvent polarity switching to drive separations with potential applications in lithium purification and recycling.

Uniform Nanowires Containing a Heterogeneousπ-Conjugated Core of Controlled Length, Composition and Morphology.

In this work, it is demonstrated for the first time that heterojunction nanowires, consisting of a gradient and segmented-like heterogeneous π-conjugated core with controllable length, composition and morphology, can be generated by co-self-seeding of oligo(p-phenylene vinylene) (OPV)- and oligo(p-phenylene ethynylene) (OPE)-containing block copolymers in spite of different chain lengths and molecular conformation for OPE and OPV. More importantly, based on the understanding of the formation of heterogeneous core by the co-self-seeding approach, a "heating/cooling" seeded growth route was developed, by which linear and branched heterojunction nanowires containing a segmented heterogeneous π-conjugated core of controlled length, composition and morphology can be obtained. This work provides a versatile platform to generate heterojunction nanowires with excellent controllability in length, composition, and morphology.

Continuous and Segmented Semiconducting Fiber-like Nanostructures with Spatially Selective Functionalization by Living Crystallization-Driven Self-Assembly.

Fiber-like π-conjugated nanostructures are important components of flexible organic electronic and optoelectronic devices. To broaden the range of potential applications, one needs to control not only the length of these nanostructures, but the introduction of diverse functionality with spatially selective control. Here we report the synthesis of a crystalline-coil block copolymer of oligo(p-phenylenevinylene)-b-poly(2-vinylpyridine) (OPV5 -b-P2VP44 ), in which the basicity and coordinating/chelating ability of the P2VP segment provide a landscape for the incorporation of a variety of functional inorganic NPs. Through a self-seeding strategy, we were able to prepare monodisperse fiber-like micelles of OPV5 -b-P2VP44 with lengths ranging from 50 to 800 nm. Significantly, the exposed two ends of OPV core of these fiber-like micelles remained active toward further epitaxial deposition of OPV5 -b-PNIPAM49 and OPV5 -b-P2VP44 to generate uniform A-B-A and B-A-B-A-B segmented block comicelles with tunable lengths for each block. The P2VP domains in these (co-)micelles can be selectively decorated with inorganic and polymeric nanoparticles as well as metal oxide coatings, to afford hybrid fiber-like nanostructures. This work provides a versatile strategy toward the fabrication of narrow length dispersity continuous and segmented π-conjugated OPV-containing fiber-like micelles with the capacity to be decorated in a spatially selective way with varying functionalities.

Mechanistic study of the formation of fiber-like micelles with a π-conjugated oligo(p-phenylenevinylene) core.

HYPOTHESIS: Crystallization-driven self-assembly (CDSA) of block copolymers (BCPs) with a crystallizable core-forming oligo(p-phenylenevinylene) (OPV) segment can be a powerful strategy for the preparation of uniform fiber-like nanostructures containing a π-conjugated core with controlled dimension and composition. However, the self-assembly landscape can be complex, and our understanding of the nucleation and growth processes in the CDSA of BCPs with a crystalline π-conjugated segment is limited. EXPERIMENTS: We used fluorescence spectroscopy and 1H NMR to follow the self-assembly of oligo(p-phenylenevinylene)-b-poly(N-isopropyl acrylamide) (OPV5-b-PNIPAM49), a typical π-conjugated-coil BCP, as solution of the BCP in ethanol is cooled from 80 °C to 23 °C and allowed to age, µDSC to monitor the crystallization exotherm, and DLS and TEM to follow micelle growth. We see a striking difference in the experiments that monitor unimer in solution comparing to those that monitor micelle growth. We see nearly complete disappearance of unimer within 30 min upon cooling. In contrast, the micelles continue to grow, increasing in length by a factor of ten over the next several hours. We are able to exclude growth by end-to-end coupling. FINDINGS: We propose a self-assembly mechanism in which short semi-crystalline rod-like micelles form upon cooling, accompanied by small amorphous aggregates. Unimers that dissociate from these aggregates subsequently deposit on the growing ends of the core-crystalline micelles. We also find that the length of the PNIPAM block affects the elongation kinetics of OPV5-b-PNIPAM.

Self-Assembled Helical and Twisted Nanostructures of a Preferred Handedness from Achiral π-Conjugated Oligo( p-phenylenevinylene) Derivatives.

The formation of chiral nanostructures from the self-assembly of achiral building blocks without external symmetry breaking inducing factors is believed to associate with the origin of chirality. Herein, we reported the synthesis and self-assembly of oligo( p-phenylenevinylene)- b-poly(ethylene glycol) (OPV3- b-PEG17, the subscripts represent the number of repeat unit of each block) in solution. We systematically examined the influence of solvent, heating temperature, and concentration of OPV3- b-PEG17 on the self-assembly of OPV3- b-PEG17 by UV/vis absorption and fluorescence spectrometry, circular dichroism technique, and transmission electron and atomic force microscopy. Interestingly, helical and twisted nanoribbons and nanotubes of a preferred handedness can be formed from achiral OPV3- b-PEG17 in the mixture of water/ethanol (v/v = 1/1) and the solution showed an obvious exciton-coupled bisignated signal, which indicated that symmetry breaking occurred during the formation of these nanostructures without external inducing factors. Our results showed that the occurrence of symmetry breaking is subtle to the experimental factors including solvent, heating temperature, and concentration of OPV3- b-PEG17. The directional π-π stacking along with steric repulsion between PEG domains should be the driving force for the formation of these chiral nanostructures. The occurrence of statistical fluctuations in the initial stage of self-assembly led to an accidental excess of helical or/and twisted structures, that is, symmetry breaking. Subsequently, the autocatalysis effect resulted in the formation of helical or/and twisted nanoribbons with a preferred handedness.

Monodisperse Fiber-like Micelles of Controlled Length and Composition with an Oligo(p-phenylenevinylene) Core via "Living" Crystallization-Driven Self-Assembly.

We report the preparation of a series of fiber-like micelles of narrow length distribution with an oligo(p-phenylenevinylene) (OPV)-core and a poly(N-isopropylacrylamide) (PNIPAM) corona via two different crystallization-driven self-assembly (CDSA) strategies. The average length Ln of these micelles can be varied up to 870 nm by varying the temperature in self-seeding experiments. In addition, seeded growth was employed not only to prepare uniform micelles of controlled length, but also to form fiber-like A-B-A triblock comicelles with an OPV-core.