We report the first experimental characterization of isomerically pure and pristine C120 fullertubes, [5,5] C120-D5d(1) and [10,0] C120-D5h(10766). These new molecules represent the highest aspect ratio fullertubes isolated to date; for example, the prior largest empty cage fullertube was [5,5] C100-D5d(1). This increase of 20 carbon atoms represents a gigantic leap in comparison to three decades of C60–C90 fullerene research. Moreover, the [10,0] C120-D5d(10766) fullertube has an end-cap derived from C80-Ih and is a new fullertube whose C40 end-cap has not yet been isolated experimentally. Theoretical and experimental analyses of anisotropic polarizability and UV–vis assign C120 isomer I as a [5,5] C120-D5d(1) fullertube. C120 isomer II matches a [10,0] C120-D5h(10766) fullertube. These structural assignments are further supported by Raman data showing metallic character for [5,5] C120-D5d(1) and nonmetallic character for C120-D5h(10766). STM imaging reveals a tubular structure with an aspect ratio consistent with a [5,5] C120-D5d(1) fullertube. With microgram quantities not amenable to crystallography, we demonstrate that DFT anisotropic polarizability, augmented by long-accepted experimental analyses (HPLC retention time, UV–vis, Raman, and STM) can be synergistically used (with DFT) to down select, predict, and assign C120 fullertube candidate structures. From 10 774 mathematically possible IPR C120 structures, this anisotropic polarizability paradigm is quite favorable to distinguish tubular structures from carbon soot. Identification of isomers I and II was surprisingly facile, i.e., two purified isomers for two possible structures of widely distinguishing features. These metallic and nonmetallic C120 fullertube isomers open the door to both fundamental research and application development.
The newly reported purification and isolation of pristine and unfunctionalized C90 and C100 fullertubes has generated excitement due to their unique “hybrid” structure of ½-fullerene endcaps, but with a single wall nanotubular belt and mid-section. Unique features of these fullertubes include a (1) defined molecular weight, (2) reproducible structure, (3) pristine tubular belt region, and (4) natural solubility into organic solvents without functionalization or polymer wrapping. Hence, the surface of the fullertube belt region would inherently be smooth and free from surface coatings, derivatization, or oxidation. These features provide a unique molecular architecture for investigating the true nature of electronic and photophysical properties of the fullertube's tubular belt. In this presentation, we will discuss our lab’s recent progress toward the isolation of segmentally longer fullertubes of higher aspect ratios as we seek to move from C120 fullertubes to C150 fullertubes and beyond. Figure 1
The emergence of macroscopic amounts of C60 fullerenes and carbon nanotubes in the 1990s has led to an explosion of growth in new structures of carbon nanomaterials. Over the last decades, there have been theoretical predictions of a particular “hybrid” family of mathematical structures. Fullertubes represent a new area of fundamental research in molecular carbon. They are similar to fullerenes in structure, but with increasingly long cylindrical, single-wall nanotube belts in the middle of the molecules. These nanotube belts are similar to single-layer, rolled graphene. In 2020 we published the isomeric separation and characterization of [5,5] C90-D5h fullertubes and [5,5] C100-D5d fullertubes. In this presentation, we will report and discuss the first isolation and UV-vis characterization of pristine and unfunctionalized C120 fullertubes. The separation and isolation of larger fullertubes is a two-step purification process. First, the spheroidal fullerene contaminants must be removed from the carbon soot extract to enrich the sample in fullertubes. Then in the second step, HPLC is used to achieve isomerically purified and pristine fullertubes. Efforts to characterize these newly isolated C120 fullertubes are currently underway.
The fullertubes represent an exciting new type of molecular carbon. This unique structure consists of a nanotube belt similar to a rolled graphene substructure, but with two fullerene based endcaps. The demand for purified fullertubes is based on the excitement of application development and fundamental research. Regardless of the desired experiment, the first requirement is to obtain isomerically purified fullertubes. In this presentation, we discuss the separation challenges and solutions to these technical hurdles. We have overcome the low fullertube abundance in soot extract by a chemical based enrichment. In this selective reaction, spheroidal fullerenes are reacted and removed from solution. The unreacted fullertubes remain in solution and are enriched by several orders of magnitude. This precleanup step is critical and should be scalable to industry.
Fullertube structures do indeed possess an elegant molecular architecture. Fullertubes also represent a new type of carbon allotrope that merges structural subunits of part fullerene and part nanotube. With fullerenyl endcaps and a nanotubyl belt region resembling a single layer of rolled graphene, fullertubes are highly anticipated to exhibit unique properties for use in multiple application areas (e.g., electronics, pharmaceuticals, etc). The first priority, however, is developing an approach to isolate large amounts of pristine, unfunctionalized samples of isomeric purity. This need for sample availability must be addressed before fundamental science and industrial research and development (R&D) can be effectively pursued. In this presentation, I will discuss separation strategies for purifying macroscopic quantities of isomerically purified fullertubes. We are making progress in expanding the fullertube length (i.e., increasing the aspect ratio) while maintaining a constant tubular diameter comparable to the diameter of C60. We will also discuss our latest results for chemically purifying new structural isomers of longer fullertubes......e.g., beyond C90-D5h(1) and C100-D5d(1) toward C120 isomers.
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