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2017 ; 11
(3
): 2509-2520
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Stop-Frame Filming and Discovery of Reactions at the Single-Molecule Level by
Transmission Electron Microscopy
#MMPMID28191929
Chamberlain TW
; Biskupek J
; Skowron ST
; Markevich AV
; Kurasch S
; Reimer O
; Walker KE
; Rance GA
; Feng X
; Müllen K
; Turchanin A
; Lebedeva MA
; Majouga AG
; Nenajdenko VG
; Kaiser U
; Besley E
; Khlobystov AN
ACS Nano
2017[Mar]; 11
(3
): 2509-2520
PMID28191929
show ga
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.