Supramolecular Functionalization of Single-Walled Carbon Nanotubes (SWNTs) with Dithieno[3,2-b:2′,3′-d]pyrrole (DTP) Containing Conjugated Polymers

Investigation of the dithieno[3,2-b:2′,3′-d]pyrrole polymerization using cross-coupling and cationic mechanisms

In this manuscript, several methodologies to obtain a living polymerization of dithieno[3,2-b:2′,3′-d]pyrrole are investigated.

π-Conjugated polymers with pendant coumarins: design, synthesis, characterization, and interactions with carbon nanotubes

A series of new fluorene-based π-conjugated polymers having coumarin derivatives as part of dendritic side chains were designed and prepared using the Suzuki–Miyaura cross-coupling reaction. A new coumarin derivative bearing a heptyl side chain for solubility was utilized to ensure solubility of the final polymers. It was found that fluorescence resonance energy transfer (FRET) from the coumrains to the polyfluorene backbone was efficient, especially for the polymers decorated with lower-generation dendrons. Each of the polymers was found to interact strongly with the surface of single-walled carbon nanotubes (SWNTs) in THF, and their ability to selectively disperse specific SWNT chiralities was investigated. Photoluminescence studies revealed that the strong polymer emission is efficiently quenched in the corresponding supramolecular complexes with SWNTs. This high quenching efficiency indicates that the coumarin–polymer FRET system can be supramolecularly bound to the surface of (SWNTs to produce an energy transfer system in which the energy absorbed by the donor coumarin chromophores is channeled to the SWNTs.

Facile Isolation of Adsorbent-Free Long and Highly-Pure Chirality-Selected Semiconducting Single-Walled Carbon Nanotubes Using A Hydrogen-bonding Supramolecular Polymer

The ideal form of semiconducting-single-walled carbon nanotubes (sem-SWNTs) for science and technology is long, defect-free, chirality pure and chemically pure isolated narrow diameter tubes. While various techniques to solubilize and purify sem-SWNTs have been developed, many of them targeted only the chiral- or chemically-purity while sacrificing the sem-SWNT intrinsic structural identities by applying strong ultra-sonication and/or chemical modifications. Toward the ultimate purification of the sem-SWNTs, here we report a mild-conditioned extraction of the sem-SWNTs using removable supramolecular hydrogen-bonding polymers (HBPs) that are composed of dicarboxylic- or diaminopyridyl-fluorenes with ~70%-(8,6)SWNT selective extraction. Replacing conventional strong sonication techniques by a simple shaking using HPBs was found to provide long sem-SWNTs (>2.0 μm) with a very high D/G ratio, which was determined by atomic force microscopy observations. The HBPs were readily removed from the nanotube surfaces by an outer stimulus, such as a change in the solvent polarities, to provide chemically pure (8,6)-enriched sem-SWNTs. We also describe molecular mechanics calculations to propose possible structures for the HBP-wrapped sem-SWNTs, furthermore, the mechanism of the chiral selectivity for the sorted sem-SWNTs is well explained by the relationship between the molecular surface area and mass of the HBP/SWNT composites.

Effect of side-chain halogenation on the interactions of conjugated polymers with SWNTs

Halogenation of polyfluorene side-chain ends with bromine or iodine causes significant differences in the nanotube species that are dispersed in solvent, indicating that subtle changes in polymer structure can affect polymer-nanotube interactions.

Effects of the chemical structure of polyfluorene on selective extraction of semiconducting single-walled carbon nanotubes

The selective recognition/extraction of semiconducting (sem)- and metallic (met)-single-walled carbon nanotubes (SWNTs) is still a great challenge in the science and technology of carbon nanotubes because their selective synthesis is still difficult. Poly(9,9-dioctyl-fluorene-2,7-diyl) (2C8-PF) and its derivatives are widely used polymers in carbon nanotube science and technology since they only extract sem-SWNTs from the mixture of sem-/met-SWNTs, while the separation mechanism is still unclear. In this study, we focus on the alkyl chain number on the polyfluorenes (PFs) to understand the mechanism for selective recognition. Here we describe the synthesis of mono-octyl moiety-carrying polyfluorene (poly(9-octyl-9H-fluorene-2,7-diyl), C8H-PF), and characterized its selective SWNT recognition/extraction ability, and found that the C8H-PF solubilized sem-SWNTs with a diameter of 0.9-1.1 nm, whose behavior is similar to that of 2C8-PF. In addition, C8H-PF selectively extracted sem-SWNTs with larger diameters (average diameter = 1.4 nm), whose behavior is different from that of 2C8-PF. Molecular mechanics simulations were carried out to understand such specific solubilization behavior. This study provides an insight into the design and synthesis of PF-based polymers and copolymers that exhibit efficient selective sem-SWNT recognition/extraction ability and their applications.

Designing large-plane conjugated copolymers for the high-yield sorting of semiconducting single-walled carbon nanotubes

Semiconducting single-walled carbon nanotubes could be selectively dispersed with a novel fluorene-peri-xanthenoxanthene conjugated copolymer. The fabricated thin-film field effect transistors show excellent and uniform performances with on/off ratios of >10(7) and mobilities of 4-6.1 cm(2) V(-1) s(-1).

Joint electrical, photophysical, and photovoltaic studies on truxene dye-sensitized solar cells: impact of arylamine electron donors

The judicious design of electron donors is one of the viable tactics to improve the efficiency of organic dyes for dye-sensitized solar cells (DSCs) employing outer-sphere redox couples. Herein, a hexahexyltruxene-substituted 4-(hexyloxy)-N-phenylaniline (HT-HPA) segment is constructed and employed as the electron donor in two organic push-pull dyes (M28 and M29) with high molar absorption coefficient values. Relative to its congener (C241) possessing the dihexyloxy-substituted triphenylamine electron donor, M29 exhibits red-shifted absorption as well as enhanced maximum molar absorption coefficient values. A thorough comparison with M29 and C241 demonstrates that the HT-HPA segment adequately insulates the TiO2 surface from the electrolyte, which prevents back-recombination and prolongs electron lifetime in the semiconductor. The diminishment of charge recombination not only enables attainment of strikingly high photovoltages (approaching 1 V), but also overcompensates the disadvantageous impact of lower dye-load amounts. As a result, the dye transformation from C241 to M29 brings forth an efficiency improvement from 7.3 % to 8.5 % at the 100 mW cm(-2) simulated AM1.5 conditions. Our work should shed light on the future design of more powerful push-pull organic photosensitizers for iodine-free DSCs.

Highly Selective Dispersion of Single-Walled Carbon Nanotubes via Polymer Wrapping: A Combinatorial Study via Modular Conjugation

Fourteen different "hairy-rod" conjugated polymers, 9,9-dioctylfluorene derivatives entailing 1,2,3-triazole, azomethine, ethynyle, biphenyle, stilbene, and azobenzene lateral units, are synthesized via modular conjugation and are systematically investigated with respect to their ability to selectively disperse SWCNTs. Four polymers of the azomethine type, with unprecedented selectivity toward dispersing (8,7), (7,6), and (9,5) SWCNT species, have been identified. In particular, azomethine polymers, herein applied for the first time for SWCNT dispersion, have been evidenced to be very effective in the highly selective solubilization of SWCNTs. The experimentally observed selectivity results are unambiguously supported by molecular dynamics simulations that account for the geometrical properties and deformation energy landscape of the polymer. Specifically, the calculations accurately and with high precision predict the experimentally observed selectivity for the (7,6) and (9,5) conformations.

Selective and reversible noncovalent functionalization of single-walled carbon nanotubes by a pH-responsive vinylogous tetrathiafulvalene-fluorene copolymer

A vinylogous tetrathiafulvalene (TTFV) monomer was prepared and copolymerized with fluorene to give a conformationally switchable conjugated copolymer. This copolymer was shown to undergo a conformational change upon protonation with trifluoroacetic acid (TFA). When mixed with single-walled carbon nanotubes (SWNTs), this TTFV-fluorene copolymer exhibited strong interactions with the SWNT surface, leading to stable, concentrated nanotube dispersions in toluene. Photoluminescence excitation mapping indicated that the copolymer selectively disperses low-diameter SWNTs, as would be expected from its ability to form a tightly coiled conformation on the nanotube surface. Addition of TFA to the copolymer-SWNT dispersion resulted in a rapid conformational change and desorption of the polymer from the SWNT surface, resulting in precipitation of pure SWNTs that were completely free of polymer. Importantly, the nanotubes isolated after dispersion and release by the TTFV-fluorene copolymer were more pure than the original SWNTs that were initially dispersed.

Effective solubilization of single-walled carbon nanotubes in THF using PEGylated corannulene dispersant

PEG-derivatized corannulene compound has been found to be very effective in solubilizing single-walled carbon nanotubes in tetrahydrofuran. Solubilizing efficiency is close to the commonly used anionic surfactant, sodium dodecyl sulfate (SDS). Corannulene derivative has also been found to have a tendency to disperse metallic nanotubes more effectively than the SDS counterpart. Theoretical calculations predict higher dispersion interactions of corannulene backbone with the convex surface of nanotubes in comparison to those calculated with other commonly used polyaromatic hydrocarbon derivatives.