We report an approach, named chemTEM, to follow chemical transformations at the single-molecule level with the electron beam of a transmission electron microscope (TEM) applied as both a tunable source of energy and a sub-angstrom imaging probe. Deposited on graphene, disk-shaped perchlorocoronene molecules are precluded from intermolecular interactions. This allows monomolecular transformations to be studied at the single-molecule level in real time and reveals chlorine elimination and reactive aryne formation as a key initial stage of multistep reactions initiated by the 80 keV e-beam. Under the same conditions, perchlorocoronene confined within a nanotube cavity, where the molecules are situated in very close proximity to each other, enables imaging of intermolecular reactions, starting with the Diels–Alder cycloaddition of a generated aryne, followed by rearrangement of the angular adduct to a planar polyaromatic structure and the formation of a perchlorinated zigzag nanoribbon of graphene as the final product. ChemTEM enables the entire process of polycondensation, including the formation of metastable intermediates, to be captured in a one-shot “movie”. A molecule with a similar size and shape but with a different chemical composition, octathio[8]circulene, under the same conditions undergoes another type of polycondensation via thiyl biradical generation and subsequent reaction leading to polythiophene nanoribbons with irregular edges incorporating bridging sulfur atoms. Graphene or carbon nanotubes supporting the individual molecules during chemTEM studies ensure that the elastic interactions of the molecules with the e-beam are the dominant forces that initiate and drive the reactions we image. Our ab initio DFT calculations explicitly incorporating the e-beam in the theoretical model correlate with the chemTEM observations and give a mechanism for direct control not only of the type of the reaction but also of the reaction rate. Selection of the appropriate e-beam energy and control of the dose rate in chemTEM enabled imaging of reactions on a time frame commensurate with TEM image capture rates, revealing atomistic mechanisms of previously unknown processes.
as excellent nanoscale containers for mole cules, [4][5][6] metals, [7][8][9] and metal halides, [10] where the spontaneous encapsulation is driven by van der Waals forces that stabilize the confined guest species in the internal channel of the host nanotube. [11] Moreover, a good geometric fit between the critical dimensions of the encapsulated guest and the internal dimensions of the host can result in van der Waals forces that are sufficiently high that insertion is irreversible. This effective nanoscale confinement permits the study of the structure, [12,13] motion, [14] and dynamics [15,16] of individual molecules.Furthermore, extreme spatial confinement in CNTs allows us to probe the kinetics and pathways of chemical reactions and processes at the nanoscale, including the formation of 1D materials templated by the internal channel of the host nanotube. [6,17,18] The simplest and most widely studied confined transformation in single-walled carbon nanotubes (SWCNTs) is the conversion of C 60 @SWCNT, so-called "peapods," into double-walled carbon nanotubes (DWCNTs) via the thermally activated polymerization and coalescence of guest fullerenes to an internal carbon nanotube. [17,19] Numerous more complex processes have also been observed inside nanotubes, such as unusual oligomerization and polymerization reactions, [13,20,21] the growth of graphene nanoribbons, [22][23][24] and the formation of molecular nanodiamonds [18] from encapsulated fullerenes and organic molecules, respectively. As such, chemical reactions inside carbon nanotubes open up new avenues for the synthesis of nanoscale materials with unique structures and functional properties inaccessible by other means.Boron nitride nanotubes (BNNTs) are isoelectronic to CNTs and similarly possess high mechanical strength [25] and excellent chemical and thermal stabilities. [26] In contrast to CNTs, however, BNNTs are electronically insulating, a consequence of the partly ionic interatomic BN bonding, and optically transparent with a wide bandgap. [27,28] While less well explored relative to CNTs, BNNTs represent a remarkable class of 1D nanoscale containers for metals, [29][30][31][32][33][34] metal halides, [35,36] and molecules, such as C 60 , [37] and owing to their transparency to visible light The use of boron nitride nanotubes as effective nanoscale containers for the confinement and thermal transformations of molecules of C 60 -fullerene is demonstrated. The gas-phase insertion of fullerenes into the internal channel of boron nitride nanotubes yields quasi-1D arrays, with packing arrangements of the guest fullerenes different from those in the bulk crystal and critically dependent on the internal diameter of the host nanotube. Interestingly, the confined fullerene molecules: i) exhibit dynamic behavior and temperaturedependent phase transitions analogous to that observed in the bulk crystal, and ii) can be effectively removed from within the internal channel of nanotubes by excessive sonication in organic solvent, indicating weak host-guest inter ...
The scalable process described by Graham A. Rance, Andrei N. Khlobystov, and co‐workers in article number https://doi.org/10.1002/smtd.201700184 affords an electrically conducting carbon nanotube confined within an insulating boron nitride nanotube through selective confinement and transformation of C60‐fullerenes inside boron nitride nanotube nanoreactors. The preparation toward and potential applications of the world's smallest co‐axial cable are conceptualized and presented. Cover image by Dr Scott Miners.
Nanotubes have been extensively utilized as nanocontainers for molecules and as nanoreactors for chemical reactions in confinement, with the potential for applications in hydrogen storage and catalysis. We show that phonon polaritons of boron nitride nanotubes (BNNTs) enhance the near-field vibrational spectra of molecules in close proximity to the surface. By encapsulating C60 fullerene in BNNTs, we reach a sensitivity level of a few hundred molecules. Furthermore, we show by the photopolymerization of C60 that products of chemical reactions inside the tubes can be identified, so long as their vibrational signatures lie in the reststrahlen band of the BNNT.
Hybrid materials composed of single walled carbon nanotubes (SWCNTs) as hollow containers and small molecules as fillers possess intriguing physical and chemical properties. Infrared spectroscopy is a useful method in most cases to characterize hybrid systems; however, regardless of the type of small molecule encapsulated in the SWCNT, the IR spectrum of the hybrid system remains silent. The possible explanation involves the highly polarizable normalπ‐electron system of the SWCNTs. Image charges induced in the SWCNT walls cancel out the transition dipole moment of the molecular vibrations resulting in the cloaking of the material inside the nanotube. To confirm the role of the delocalized normalπ‐electron system in this process, insulating boron nitride nanotubes filled with C60 were also investigated and found to be transparent to infrared radiation. We have also demonstrated the cloaking effect in two dimensions using a thin film of C60 covered by single layer graphene. The significance of our results lies in the fact that the cloaking layer is a real material, not a metamaterial.
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