Direct Microscopic Analysis of Individual C₆₀ Dimerization Events: Kinetics and Mechanisms

Abstract

Modern transition state theory states that the statistical behavior of a chemical reaction is the sum of individual chemical events that occur randomly. Statistical analysis of each event for individual molecules in a three-dimensional space however is practically impossible. We report here that kinetics and mechanisms of chemical reactions can be investigated by using a one-dimensional system where reaction events can be observed in situ and counted one by one using variable-temperature (VT) atomic-resolution transmission electron microscopy (TEM). We thereby provide direct proof that the ensemble behavior of random events conforms to the Rice-Ramsperger-Kassel-Marcus theory, as illustrated for [2 + 2] cycloaddition of C molecules in carbon nanotubes (CNTs). This method gives kinetic and structural information for different types of reactions occurring simultaneously in the microscopic view field, suggesting that the VT-TEM opens a new dimension of chemical kinetics research on molecules and their assemblies in their excited and ionized states. The study carried out at 393-493 K showed that pristine CNT primarily acts as a singlet sensitizer of the cycloaddition reaction that takes place with an activation energy of 33.5 ± 6.8 kJ/mol. On the other hand, CNT suffers electron damage of the conjugated system at 103-203 K and promotes a reactive radical cation path that takes place with an activation energy of only 1.9 ± 0.7 kJ/mol. The pre-exponential factor of the Arrhenius plot gave us further mechanistic insights.

Real-Time Video Imaging of Mechanical Motions of a Single Molecular Shuttle

“…9 Second, the translation events are synchronized to the CNT vibration, taking place stochastically a few to several times per minute at both 298 K and 423 K. This temperature insensitivity of the frequency of the translation stands in sharp contrast to the temperaturedependence of the reaction rate of the C60 dimerization reaction. 13 Third, each translation event took place only when the CNT vibrated at its maximum amplitude, while many other vibrational events did not cause translation, indicating that neither direct electron bombardment of the fullerene molecule nor CNT deformation (see above) is not the cause of the translation. Fourth, all translation events accompanied longitudinal molecular rotation (direction of the rotation unknown at this time).…”

A Conversion Dynamics of (C60)2 Dimer Fullerenes to a Fused Dimer Cage in Carbon Nanopeapods: Tight‐Binding Molecular Dynamics Simulation

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2 dimer fullerenes to fused cages in a single-walled nanotube, Nanopeapod

Using the internal space of the within single-walled carbon nanotube (SWNT) as a nanometer-scale reaction chamber, double-walled carbon nanotubes (DWNTs) forming secondary tubes inside the SWNT have been reported. 6 The exact mechanism behind the formation of carbon materials is difficult to elucidate because the control of many of the experimental conditions is still challenging. 1,2 Molecular dynamics are an important way to understand the chemical reaction process of SWNT.

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“…It can be explained quantitatively that the DWNT is made through the decomposition and conversion process of C 60 molecules arranged in the form of a chain within an SWNT. 5,6 Using HR TEM techniques, molecular motion and their conformational changes, the chemical reaction to dimerization of fullerene in SWNT were reported. 3,4 Chemical reactions by monitoring time-dependent changes in the atomic position that respond to molecules for the study of the bifurcation reaction of fullerenes inside carbon nanotubes were visualized by the high-resolution transmission electron microscopy (HR TEM) was used as a function of electron dose.…”

“…1,2 Molecular dynamics are an important way to understand the chemical reaction process of SWNT. 6 The exact mechanism behind the formation of carbon materials is difficult to elucidate because the control of many of the experimental conditions is still challenging. 5,6 Using HR TEM techniques, molecular motion and their conformational changes, the chemical reaction to dimerization of fullerene in SWNT were reported.…”

“…Figure 3 shows the geometrical spatial arrangement of the (C 60 ) 2 fullerene dimer molecule inside the SWNT indicating the unit cell of CNP under the periodic condition for TBMD simulation as a function of dynamic time; that is, for 12.744 ps at the temperature of 5000 K. If you take a closer look at this process, the separate (C 60 ) 2 fullerene dimer molecules form a single bond between C 60 fullerene, the carbon atoms from the C 60 fullerene move to a different C 60 fullerene to form a new bond, and as the C 60 fullerene and the broken, the carbon pieces form a new bond with the other C 60 fullerene, gradually forming a small capped carbon nanotube. 6 Therefore, it can be suggested that the scenario in which (C 60 ) 2 @SWNT forms C 120 @SWNT (a fused dimer inside SWNT) could be followed by the deformation and fragmentation of C 60 and then the fusion of (C 60 ) 2 dimer after the coupling took place between one C 60 and SWNT of (C 60 ) 2 @SWNT in the initial stage. 6 Therefore, it can be suggested that the scenario in which (C 60 ) 2 @SWNT forms C 120 @SWNT (a fused dimer inside SWNT) could be followed by the deformation and fragmentation of C 60 and then the fusion of (C 60 ) 2 dimer after the coupling took place between one C 60 and SWNT of (C 60 ) 2 @SWNT in the initial stage.…”