5 research outputs found
Dehalogenative Homocoupling of Terminal Alkynyl Bromides on Au(111): Incorporation of Acetylenic Scaffolding into Surface Nanostructures
On-surface
C鈥揅 coupling reactions of molecular precursors with alkynyl
functional groups demonstrate great potential for the controllable
fabrication of low-dimensional carbon nanostructures/nanomaterials,
such as carbyne, graphyne, and graphdiyne, which demand the incorporation
of highly active sp-hybridized carbons. Recently, through a dehydrogenative
homocoupling reaction of alkynes, the possibility was presented to
fabricate surface nanostructures involving acetylenic linkages, while
problems lie in the fact that different byproducts are inevitably
formed when triggering the reactions at elevated temperatures. In
this work, by delicately designing the molecular precursors with terminal
alkynyl bromide, we introduce the dehalogenative homocoupling reactions
on the surface. As a result, we successfully achieve the formation
of dimer structures, one-dimensional molecular wires and two-dimensional
molecular networks with acetylenic scaffoldings on an inert Au(111)
surface, where the unexpected C鈥揂u鈥揅 organometallic
intermediates are also observed. This study further supplements the
database of on-surface dehalogenative C鈥揅 coupling reactions,
and more importantly, it provides us an alternative efficient way
for incorporating the acetylenic scaffolding into low-dimensional
surface nanostructures
A 蟺鈥慍onjugated System with Flexibility and Rigidity That Shows Environment-Dependent RGB Luminescence
We have designed and synthesized
a 蟺-conjugated system that
consists of a flexible and nonplanar 蟺 joint and two emissive
rigid and planar wings. This molecular system exhibits respectively
red, green, and blue (RGB) emission from a single-component luminophore
in different environments, namely in polymer matrix, in solution,
and in crystals. The flexible unit gives rise to a dynamic conformational
change in the excited state from a nonplanar V-shaped structure to
a planar structure, leading to a dual fluorescence of blue and green
colors. The rigid and planar moieties favor the formation of a two-fold
蟺-stacked array of the V-shaped molecules in the crystalline
state, which produces a red excimer-like emission. These RGB emissions
are attained without changing the excitation energy
A 蟺鈥慍onjugated System with Flexibility and Rigidity That Shows Environment-Dependent RGB Luminescence
We have designed and synthesized
a 蟺-conjugated system that
consists of a flexible and nonplanar 蟺 joint and two emissive
rigid and planar wings. This molecular system exhibits respectively
red, green, and blue (RGB) emission from a single-component luminophore
in different environments, namely in polymer matrix, in solution,
and in crystals. The flexible unit gives rise to a dynamic conformational
change in the excited state from a nonplanar V-shaped structure to
a planar structure, leading to a dual fluorescence of blue and green
colors. The rigid and planar moieties favor the formation of a two-fold
蟺-stacked array of the V-shaped molecules in the crystalline
state, which produces a red excimer-like emission. These RGB emissions
are attained without changing the excitation energy
Competition between Hydrogen Bonds and Coordination Bonds Steered by the Surface Molecular Coverage
In
addition to the choices of metal atoms/molecular linkers and
surfaces, several crucial parameters, including surface temperature,
molecular stoichiometric ratio, electrical stimulation, concentration,
and solvent effect for liquid/solid interfaces, have been demonstrated
to play key roles in the formation of on-surface self-assembled supramolecular
architectures. Moreover, self-assembled structural transformations
frequently occur in response to a delicate control over those parameters,
which, in most cases, involve either conversions from relatively weak
interactions to stronger ones (e.g., hydrogen bonds to coordination
bonds) or transformations between the comparable interactions (e.g.,
different coordination binding modes or hydrogen bonding configurations).
However, intermolecular bond conversions from relatively strong coordination
bonds to weak hydrogen bonds were rarely reported. Moreover, to our
knowledge, a reversible conversion between hydrogen bonds and coordination
bonds has not been demonstrated before. Herein, we have demonstrated
a facile strategy for the regulation of stepwise intermolecular bond
conversions from the metal鈥搊rganic coordination bond (Cu鈥揘)
to the weak hydrogen bond (CH路路路N) by increasing the
surface molecular coverage. From the DFT calculations we quantify
that the loss in intermolecular interaction energy is compensated
by the increased molecular adsorption energy at higher molecular coverage.
Moreover, we achieved a reversible conversion from the weak hydrogen
bond to the coordination bond by decreasing the surface molecular
coverage
Direct Formation of C鈥揅 Double-Bonded Structural Motifs by On-Surface Dehalogenative Homocoupling of <i>gem</i>-Dibromomethyl Molecules
Conductive
polymers are of great importance in a variety of chemistry-related
disciplines and applications. The recently developed bottom-up on-surface
synthesis strategy provides us with opportunities for the fabrication
of various nanostructures in a flexible and facile manner, which could
be investigated by high-resolution microscopic techniques in real
space. Herein, we designed and synthesized molecular precursors functionalized
with benzal聽<i>gem</i>-dibromomethyl groups. A combination
of scanning tunneling microscopy, noncontact atomic force microscopy,
high-resolution synchrotron radiation photoemission spectroscopy,
and density functional theory calculations demonstrated that it is
feasible to achieve the direct formation of C鈥揅 double-bonded
structural motifs <i>via</i> on-surface dehalogenative homocoupling
reactions on the Au(111) surface. Correspondingly, we convert the
sp<sup>3</sup>-hybridized state to an sp<sup>2</sup>-hybridized state
of carbon atoms, <i>i</i>.<i>e</i>., from an alkyl
group to an alkenyl one. Moreover, by such a bottom-up strategy, we
have successfully fabricated poly颅(phenylenevinylene) chains on the
surface, which is anticipated to inspire further studies toward understanding
the nature of conductive polymers at the atomic scale