Structural Tuning of Curved TTFAQ-AQ as a Redox-Active Supramolecular Partner for C70 Fullerene

A series of saddle-shaped donor-acceptor π-systems, termed TTFAQ-AQs, were designed and synthesized. The molecular structures of TTFAQ-AQs feature a π-fused framework containing an anthraquinodimethane extended tetrathiafulvalene (TTFAQ) as the donor and an anthraquinone (AQ) unit as the acceptor. As such, TTFAQ-AQs show enhanced intramolecular charge-transfer properties, which result in amphoteric redox behavior and narrow electronic energy band gaps. Detailed structural and electronic properties were investigated by UV-vis absorption, cyclic voltammetric, and single-crystal X-ray diffraction (SCXRD) analyses. The supramolecular interactions of TTFAQ-AQs with C₆₀ and C₇₀ fullerenes were examined in both the solution and solid phases. Our results showed that the benzoannulated TTFAQ-AQ derivative favors interaction with C₇₀ fullerene through complementary concave-convex interactions. Detailed energetics involved in the TTFAQ-AQ/C₇₀ interactions were assessed by means of density functional theory (DFT) calculations.

Separation of Semiconducting Carbon Nanotubes Using Conjugated Polymer Wrapping

In the past two decades, single-walled carbon nanotubes (SWNTs) have been explored for electronic applications because of their high charge carrier mobility, low-temperature solution processability and mechanical flexibility. Semiconducting SWNTs (s-SWNTs) are also considered an alternative to traditional silicon-based semiconductors. However, large-scale, as-produced SWNTs have poor solubility, and they are mixtures of metallic SWNTs (m-SWNTs) and s-SWNTs, which limits their practical applications. Conjugated polymer wrapping is a promising method to disperse and separate s-SWNTs, due to its high selectivity, high separation yield and simplicity of operation. In this review, we summarize the recent progress of the conjugated polymer wrapping method, and discuss possible separation mechanisms for s-SWNTs. We also discuss various parameters that may affect the selectivity and sorting yield. Finally, some electronic applications of polymer-sorted s-SWNTs are introduced. The aim of this review is to provide polymer chemist a basic concept of polymer based SWNT separation, as well as some polymer design strategies, influential factors and potential applications.

Chirality Pure Carbon Nanotubes: Growth, Sorting, and Characterization

Single-walled carbon nanotubes (SWCNTs) have been attracting tremendous attention owing to their structure (chirality) dependent outstanding properties, which endow them with great potential in a wide range of applications. The preparation of chirality-pure SWCNTs is not only a great scientific challenge but also a crucial requirement for many high-end applications. As such, research activities in this area over the last two decades have been very extensive. In this review, we summarize recent achievements and accumulated knowledge thus far and discuss future developments and remaining challenges from three aspects: controlled growth, postsynthesis sorting, and characterization techniques. In the growth part, we focus on the mechanism of chirality-controlled growth and catalyst design. In the sorting part, we organize and analyze existing literature based on sorting targets rather than methods. Since chirality assignment and quantification is essential in the study of selective preparation, we also include in the last part a comprehensive description and discussion of characterization techniques for SWCNTs. It is our view that even though progress made in this area is impressive, more efforts are still needed to develop both methodologies for preparing ultrapure (e.g., >99.99%) SWCNTs in large quantity and nondestructive fast characterization techniques with high spatial resolution for various nanotube samples.

Recent advances in dithiafulvenyl-functionalized organic conjugated materials

This review highlights the recent studies of advanced organic π-conjugated materials that contain 1,4-dithiafulvene (DTF) as a redox-active component.

DFT investigation of the interaction between single-walled carbon nanotubes and fluorene-based conjugated oligomers

π-Conjugated oligomers with relatively short molecular backbones can be used effectively in dispersion of carbon nanotubes (CNTs). In this paper, we present a systematic study on interactions between diphenylene-fluorene oligomers (DPFs) and single-walled CNTs (SWCNTs) using density functional theory (DFT) calculations. Four DFT methods are used in this work: the long range (LR)-corrected CAM-B3LYP, the dispersion (D)-corrected B97D, the LR- and D-corrected wB97XD, and the hybrid B3LYP. The DPFs examined in this study contain different functional groups attached to the π-conjugated backbone, including two different end groups, carboxaldehyde (ALD) and dithiafulvenyl (DTF), and three different side chains (SCs), C₈H₁₇, OC₁₀H₂₁, and SC₁₀H₂₁. The computational results disclose the effects of end groups, SCs, and DFT methods on structures, dipole moments, and energetics of isolated DPFs and DPF/SWCNT combinations. Consistent with our previous study (involving oligo(p-phenylene ethynylene)s (OPEs)) [Aljohani et al., J. Phys. Chem. C, 2017, 121, 4692-4702], our results herein demonstrate that the type of end group plays a key role in determining the strength of interactions between SWNTs and conjugated oligomers. In particular, DTF-endcapped oligomers have a stronger electrostatic interaction with SWCNT than ALD-endcapped oligomers do. As a result, DTF-endcapped conjugated oligomers become more polarized than ALD-endcapped oligomers after complexing with SWCNTs. The magnitude of binding energy, on the other hand, shows dependence on the orientation of the backbone and side chains of these oligomers relative to the SWCNT which in the case of fluorene-based oligomers is not always favourable for optimal binding. This study indicates that fluorene-based oligomers might not be as good dispersants of SWCNTs as OPEs.

The role of the solvent and the size of the nanotube in the non-covalent dispersion of carbon nanotubes with short organic oligomers – a DFT study

Among different dispersants of single-walled carbon nanotubes (SWCNTs), conjugated organic oligomers have the ability to interact strongly with SWCNTs and allow for effective dispersion in several organic solvents. Recently, we have carried out two computational investigations on the intermolecular interactions between conjugated organic oligomers and SWCNTs in order to gain insight into an important process of the non-covalent dispersion of carbon nanotubes with short oligomers. These studies highlighted the fact that two additional factors, namely, the effects of the solvent and the carbon nanotube's size on these interactions need further investigation. In this work, with the help of model compounds (which are molecular fragments of the short oligomers used in our previous investigations), we analyze the significance of these two factors. We employ three dispersion corrected density functional theory (D-DFT) approximations (B97D, wB97XD, and B3LYP-D3) to assess the effect of the DFT method, and two basis sets (6-31G(d) and 6-31++G(d,p)) to assess the importance of using a higher basis set in our computations. The main focus of this work is to assess the effect of solvation and nanotube's size on the structure, electronic properties, and binding energies of the respective pairs of model compounds and segments of carbon nanotubes. No significant differences are found between the results of (6,5) and (8,7) SWCNTs in either the geometrical parameters of interacting oligomers or the general tendency of wrapping of their long side chains (SCs) around the nanotubes. However, we find that the binding energies per atom between nanotubes and model compounds are larger for nanotubes with the smaller diameter. The results of electronic properties also show that all model compounds interact more strongly with the (6,5) SWCNT than with the (8,7) SWCNT. Polar solvents such as chloroform show lower binding energies relative to those obtained without a solvent or with non-polar solvents such as hexane. It appears that the presence of a solvent weakens the oligomer/nanotube interactions and, presumably, strengthens the oligomer/solvent and nanotube/solvent interactions to facilitate dispersion of SWCNTs.

Among different dispersants of single-walled carbon nanotubes (SWCNTs), conjugated organic oligomers have the ability to interact strongly with SWCNTs and allow for effective dispersion in several organic solvents.

Recent developments in the selective dispersion of single-walled carbon nanotubes using conjugated polymers

A significant barrier that impedes the commercialization of single-walled carbon nanotube-related applications is that all known synthetic methods produce a complicated mixture of semiconducting and metallic species. For device applications, pure semiconducting or pure metallic samples are desirable. Thus far, the purification methods that have been identified are capable of separating individual carbon nanotube species on a microgram scale, but purification on a large scale has remained elusive. The use of conjugated polymers to selectively disperse specific nanotube species is a promising approach to resolve the scalability issue, but a comprehensive understanding of the selectivity mechanism has not yet been achieved. Here, several of the trends reported in the literature are outlined to further the rational design of conjugated polymers for nanotube sorting. Numerous variables influence dispersion selectivity, including polymer structure and molecular weight, nanotube type used, sonication temperature, amount of polymer relative to nanotube, and solvent. We have organized these seemingly disparate parameters into two simple categories: conjugated polymer structure, and dispersion preparation conditions. Most importantly, we consider the mechanistic arguments that have been proposed, and provide additional insights based on the observations in the literature.