16 research outputs found
Temporal fluctuations in excimer-like interactions between pi-conjugated chromophores
Inter- or intramolecular coupling processes between chromophores such as
excimer formation or H- and J-aggregation are crucial to describing the
photophysics of closely packed films of conjugated polymers. Such coupling is
highly distance dependent, and should be sensitive to both fluctuations in the
spacing between chromophores as well as the actual position on the chromophore
where the exciton localizes. Single-molecule spectroscopy reveals these
intrinsic fluctuations in well-defined bi-chromophoric model systems of
cofacial oligomers. Signatures of interchromophoric interactions in the excited
state - spectral red-shifting and broadening, and a slowing of
photoluminescence decay - correlate with each other but scatter strongly
between single molecules, implying an extraordinary distribution in coupling
strengths. Furthermore, these excimer-like spectral fingerprints vary with
time, revealing intrinsic dynamics in the coupling strength within one single
dimer molecule, which constitutes the starting point for describing a molecular
solid. Such spectral sensitivity to sub-Angstrom molecular dynamics could prove
complementary to conventional FRET-based molecular rulers
A Giant Molecular Spoked Wheel
The
modular synthesis of a defined, rigid molecular spoked wheel
structure with the sum formula C<sub>1878</sub>H<sub>2682</sub> and
a diameter of about 12 nm is described. The attached 96 dodecyl side
chains provide the solubility of the 25 260 Da compound in
common organic solvents. At the octanoic acid/highly oriented pyrolytic
graphite interface, the molecules self-assemble to form an ordered
2D lattice, which is investigated by scanning tunneling microscopy,
displaying their structure with submolecular resolution
Monodisperse Oligo(<i>p</i>‑phenylene–butadiynylene)s: GPC Conversion Factors and Self-Assembled Monolayers
Alkyl- and alkoxy-substituted <i>p</i>-phenylene–butadiynylene
tetramers, obtained via a stepwise synthesis, are polymerized under
Glaser coupling conditions. The fractionation of the oligomers by
recycling gel permeation chromatography (recGPC) yields three sets
of monodisperse oligoÂ(<i>p</i>-phenylene–butadiynylene)Âs
(OPBs) with degrees of polymerization <i>n</i> = 4, 8, 12,
..., 60. Subsequent GPC analysis of these oligomers provides three
sets of size- and substituent-dependent conversion factors that quantify
the overestimation of the oligomer molecular weight when a polystyrene
(PS) calibrated GPC system is used for the data analysis. Scanning
tunneling microscopy (STM) of representative oligomers at the solid/liquid
interface visualizes the monodispersity, the length-dependent rigidity,
and their assembling behavior
A Liquid-Crystalline Phenylene-Based Shape-Persistent Molecular Spoked Wheel
Molecular
spoked wheels with an all-phenylene backbone and different
alkoxy side chain substitution patterns were synthesized using a cobalt-catalyzed
[2 + 2 + 2] cycloaddition and subsequent template-directed cyclization
via Yamamoto coupling. The two-dimensional organization of the molecules
at the solid/liquid interface was investigated by means of scanning
tunneling microscopy, allowing imaging of the molecular structure
with submolecular resolution. With the right proportion of the flexible
alkyl corona to the rigid core, mesomorphic behavior of one compound
could be observed over a wide temperature range
Coherent and Incoherent Interactions between Cofacial Π‑Conjugated Oligomer Dimers in Macrocycle Templates
The interactions between two π-conjugated oligomers
templated
in molecular scaffolds are revealed as a function of separation and
orientation, providing models of intermolecular interactions in bulk
organic semiconductor materials. For a variety of dimer geometries
(acyclic and macrocyclic) of the same model oligomer, no change in
fluorescence spectra, fluorescence dynamics, or low-temperature single-molecule
emission characteristics is observed. A small red-shift and slowing
of fluorescence in the most closely spaced macrocyclic dimer structure
is thought to arise both due to an intramolecular solvatochromic shift
as well as from weak intramolecular aggregate formation. No corresponding
effect is observed in bulk films of the acyclic model oligomer, implying
the absence of intermolecular aggregate or excimer formation due to
random relative dipole orientations. The largest effect of intramolecular
geometry of the model dimer structures is seen in transient fluorescence
depolarization, where an open ring geometry leads to rapid depolarization,
compared to the corresponding macrocycle, due to the presence of a
range of molecular transition dipole moment orientations. Self-assembled
monolayers of the molecules on HOPG investigated by scanning-tunneling
microscopy further illustrate the conformational variability of the
open dimers in contrast to the fixed conformation of the closed dimers
Flexible Phenanthracene Nanotubes for Explosive Detection
Phenanthracene
nanotubes with arylene-ethynylene-butadiynylene
rims and phenanthracene walls are synthesized in a modular bottom-up
approach. One of the rims carries hexadecyloxy side chains, mediating
the affinity to highly oriented pyrolytic graphite. Molecular dynamics
simulations show that the nanotubes are much more flexible than their
structural formulas suggest: In 12, the phenanthracene units act as hinges that flip the two macrocycles
relative to each other to one of two possible sites, as quantum mechanical
models suggest and scanning tunneling microscopy investigations prove.
Unexpectedly, both theory and experiment show for 13 that the three phenanthracene hinges are deflected
from the upright position, accompanied by a deformation of both macrocycles
from their idealized sturdy macroporous geometry. This flexibility
together with their affinity to carbon-rich substrates allows for
an efficient host–guest chemistry at the solid/gas interface
opening the potential for applications in single-walled carbon nanotube-based
sensing, and the applicability to build new sensors for the detection
of 2,4,6-trinitrotoluene via nitroaromatic markers is shown
Flexible Phenanthracene Nanotubes for Explosive Detection
Phenanthracene
nanotubes with arylene-ethynylene-butadiynylene
rims and phenanthracene walls are synthesized in a modular bottom-up
approach. One of the rims carries hexadecyloxy side chains, mediating
the affinity to highly oriented pyrolytic graphite. Molecular dynamics
simulations show that the nanotubes are much more flexible than their
structural formulas suggest: In 12, the phenanthracene units act as hinges that flip the two macrocycles
relative to each other to one of two possible sites, as quantum mechanical
models suggest and scanning tunneling microscopy investigations prove.
Unexpectedly, both theory and experiment show for 13 that the three phenanthracene hinges are deflected
from the upright position, accompanied by a deformation of both macrocycles
from their idealized sturdy macroporous geometry. This flexibility
together with their affinity to carbon-rich substrates allows for
an efficient host–guest chemistry at the solid/gas interface
opening the potential for applications in single-walled carbon nanotube-based
sensing, and the applicability to build new sensors for the detection
of 2,4,6-trinitrotoluene via nitroaromatic markers is shown
Flexible Phenanthracene Nanotubes for Explosive Detection
Phenanthracene
nanotubes with arylene-ethynylene-butadiynylene
rims and phenanthracene walls are synthesized in a modular bottom-up
approach. One of the rims carries hexadecyloxy side chains, mediating
the affinity to highly oriented pyrolytic graphite. Molecular dynamics
simulations show that the nanotubes are much more flexible than their
structural formulas suggest: In 12, the phenanthracene units act as hinges that flip the two macrocycles
relative to each other to one of two possible sites, as quantum mechanical
models suggest and scanning tunneling microscopy investigations prove.
Unexpectedly, both theory and experiment show for 13 that the three phenanthracene hinges are deflected
from the upright position, accompanied by a deformation of both macrocycles
from their idealized sturdy macroporous geometry. This flexibility
together with their affinity to carbon-rich substrates allows for
an efficient host–guest chemistry at the solid/gas interface
opening the potential for applications in single-walled carbon nanotube-based
sensing, and the applicability to build new sensors for the detection
of 2,4,6-trinitrotoluene via nitroaromatic markers is shown
Flexible Phenanthracene Nanotubes for Explosive Detection
Phenanthracene
nanotubes with arylene-ethynylene-butadiynylene
rims and phenanthracene walls are synthesized in a modular bottom-up
approach. One of the rims carries hexadecyloxy side chains, mediating
the affinity to highly oriented pyrolytic graphite. Molecular dynamics
simulations show that the nanotubes are much more flexible than their
structural formulas suggest: In 12, the phenanthracene units act as hinges that flip the two macrocycles
relative to each other to one of two possible sites, as quantum mechanical
models suggest and scanning tunneling microscopy investigations prove.
Unexpectedly, both theory and experiment show for 13 that the three phenanthracene hinges are deflected
from the upright position, accompanied by a deformation of both macrocycles
from their idealized sturdy macroporous geometry. This flexibility
together with their affinity to carbon-rich substrates allows for
an efficient host–guest chemistry at the solid/gas interface
opening the potential for applications in single-walled carbon nanotube-based
sensing, and the applicability to build new sensors for the detection
of 2,4,6-trinitrotoluene via nitroaromatic markers is shown
Flexible Phenanthracene Nanotubes for Explosive Detection
Phenanthracene
nanotubes with arylene-ethynylene-butadiynylene
rims and phenanthracene walls are synthesized in a modular bottom-up
approach. One of the rims carries hexadecyloxy side chains, mediating
the affinity to highly oriented pyrolytic graphite. Molecular dynamics
simulations show that the nanotubes are much more flexible than their
structural formulas suggest: In 12, the phenanthracene units act as hinges that flip the two macrocycles
relative to each other to one of two possible sites, as quantum mechanical
models suggest and scanning tunneling microscopy investigations prove.
Unexpectedly, both theory and experiment show for 13 that the three phenanthracene hinges are deflected
from the upright position, accompanied by a deformation of both macrocycles
from their idealized sturdy macroporous geometry. This flexibility
together with their affinity to carbon-rich substrates allows for
an efficient host–guest chemistry at the solid/gas interface
opening the potential for applications in single-walled carbon nanotube-based
sensing, and the applicability to build new sensors for the detection
of 2,4,6-trinitrotoluene via nitroaromatic markers is shown