58 research outputs found
Design and Synthesis of Monofunctionalized, Water-Soluble Conjugated Polymers for Biosensing and Imaging Applications
Water-soluble conjugated polymers with controlled molecular weight
characteristics, absence of ionic groups, high emission quantum yields,
and end groups capable of selective reactions of wide scope are desirable
for improving their performance in various applications and, in particular,
fluorescent biosensor schemes. The synthesis of such a structure is
described herein. 2-Bromo-7-iodofluorene with octakis(ethylene glycol)
monomethyl ether chains at the 9,9′-positions, i.e., compound <b>4</b>, was prepared as the reactive premonomer. A high-yielding
synthesis of the organometallic initiator (dppe)Ni(Ph)Br (dppe = 1,2-bis(diphenylphosphino)ethane)
was designed and implemented, and the resulting product was characterized
by single-crystal X-ray diffraction techniques. Polymerization of <b>4</b> by (dppe)Ni(Ph)Br can be carried out in less than 30 s,
affording excellent control over the average molecular weight and
polydispersity of the product. Quenching of the polymerization with
[2-(trimethylsilyl)ethynyl]magnesium bromide yields silylacetylene-terminated
water-soluble poly(fluorene) with a photoluminescence quantum efficiency
of 80%. Desilylation, followed by copper-catalyzed azide–alkyne
cycloaddition reaction, yields a straightforward route to introduce
a wide range of specific end group functionalities. Biotin was used
as an example. The resulting biotinylated conjugated polymer binds
to streptavidin and acts as a light-harvesting chromophore to optically
amplify the emission of Alexa Fluor-488 chromophores bound onto the
streptavidin. Furthermore, the biotin end group makes it possible
to bind the polymer onto streptavidin-functionalized cross-linked
agarose beads and thereby incorporate a large number of optically
active segments
Effect of Modified Phospholipid Bilayers on the Electrochemical Activity of a Membrane-Spanning Conjugated Oligoelectrolyte
The
incorporation and electrochemical activity of a conjugated
oligoelectrolyte (COE) in model phospholipid bilayers have been characterized
using cyclic voltammetry and UV–vis absorption measurements.
Several other modifiers were also incorporated into the phospholipid
membranes to alter properties such as charge and alkyl chain disorder.
Using potassium ferricyanide to measure charge transport, it was observed
that bilayers that contained cholic acid, a negatively charged additive
that also promotes alkyl chain disorder, had higher COE uptake and
charge permeability than unmodified bilayers. In contrast, when the
positively charged choline was incorporated, charge permeability decreased
and COE uptake was similar to that of unmodified bilayers. The incorporation
of cholesterol at low concentrations within the phospholipid membranes
was shown to enhance the COE’s effectiveness at increasing
membrane charge permeability without increasing the COE concentration
in the bilayer. Higher concentrations of cholesterol reduce membrane
fluidity and membrane charge permeability. Collectively, these results
demonstrate that changes in phospholipid membrane charge permeability
upon COE incorporation depend not only on the concentration in the
membrane but also on interactions with the phospholipid bilayer and
other additives present in the membranes. This approach of manipulating
the properties of phospholipid membranes to understand COE interactions
is applicable to understanding the behavior of a wide range of molecules
that impart useful properties to phospholipid membranes
Book reviews RPEiS 40(1), 1978
Digitalizacja i deponowanie archiwalnych zeszytĂłw RPEiS sfinansowane przez MNiSW w ramach realizacji umowy nr 541/P-DUN/201
Impact of Regiochemistry and Isoelectronic Bridgehead Substitution on the Molecular Shape and Bulk Organization of Narrow Bandgap Chromophores
A comparison of two classes of small molecules relevant
to the
field of organic electronics is carried out at the molecular and supramolecular
levels. First, two molecules that differ only in the position of a
pyridyl N-atom within an acceptor fragment are compared and contrasted.
X-ray investigation of single crystals reveals that positioning the
pyridyl N-atoms <i>proximal</i> to the molecules center
changes the molecular shape by bending the molecule into a banana
shape. Second, we demonstrate that the banana shape of the molecule
can be controlled by replacing a Si atom within the dithienosilole
fragment with a C or Ge atom. Here, utilization of cyclopentadithiophene
or dithienogermole as the internal electron-rich unit leads to a decrease
or an increase in the bending of the conjugated backbone, respectively.
Such molecular shape changes alter intermolecular packing and thus
affect bulk properties, leading to large differences in the optical,
thermal, and crystallization properties
Impact of Regiochemistry and Isoelectronic Bridgehead Substitution on the Molecular Shape and Bulk Organization of Narrow Bandgap Chromophores
A comparison of two classes of small molecules relevant
to the
field of organic electronics is carried out at the molecular and supramolecular
levels. First, two molecules that differ only in the position of a
pyridyl N-atom within an acceptor fragment are compared and contrasted.
X-ray investigation of single crystals reveals that positioning the
pyridyl N-atoms <i>proximal</i> to the molecules center
changes the molecular shape by bending the molecule into a banana
shape. Second, we demonstrate that the banana shape of the molecule
can be controlled by replacing a Si atom within the dithienosilole
fragment with a C or Ge atom. Here, utilization of cyclopentadithiophene
or dithienogermole as the internal electron-rich unit leads to a decrease
or an increase in the bending of the conjugated backbone, respectively.
Such molecular shape changes alter intermolecular packing and thus
affect bulk properties, leading to large differences in the optical,
thermal, and crystallization properties
Impact of Regiochemistry and Isoelectronic Bridgehead Substitution on the Molecular Shape and Bulk Organization of Narrow Bandgap Chromophores
A comparison of two classes of small molecules relevant
to the
field of organic electronics is carried out at the molecular and supramolecular
levels. First, two molecules that differ only in the position of a
pyridyl N-atom within an acceptor fragment are compared and contrasted.
X-ray investigation of single crystals reveals that positioning the
pyridyl N-atoms <i>proximal</i> to the molecules center
changes the molecular shape by bending the molecule into a banana
shape. Second, we demonstrate that the banana shape of the molecule
can be controlled by replacing a Si atom within the dithienosilole
fragment with a C or Ge atom. Here, utilization of cyclopentadithiophene
or dithienogermole as the internal electron-rich unit leads to a decrease
or an increase in the bending of the conjugated backbone, respectively.
Such molecular shape changes alter intermolecular packing and thus
affect bulk properties, leading to large differences in the optical,
thermal, and crystallization properties
Molecular Considerations for Mesophase Interaction and Alignment of Lyotropic Liquid Crystalline Semiconducting Polymers
Intermolecular interactions in conjugated
polymers influence crystallinity,
self-assembly, and packing motif, factors which in turn crucially
impact charge transport properties such as carrier mobility in organic
electronic devices. Correlated alignment of molecular and crystalline
morphologies provides direct pathways for charge carriers to follow;
however, the role of intermolecular interactions in achieving this
is unexplored. Herein, we synthesize a series of lyotropic liquid
crystalline conjugated polymers with variable side-chain structure
to lend distinct steric repulsion and van der Waals attractive forces
to each mesophase. We use this to investigate the role of intermolecular
interactions on mesophase alignment. The strength of intermolecular
interaction for each mesophase is compared by measuring melting temperature,
π-stacking distance, and the Maier–Saupe interaction
parameter. In general we find that side-chain structure can impact
interaction strength by varying steric repulsion and backbone attractions
and that the Maier–Saupe interaction parameters correlate with
higher degrees of alignment after shearing, achieving a dichroic absorbance
ratio of up to 2. This observation is used to develop equilibrium
processing methods for fabricating macroscopically aligned polymer
substrates used in transistors, improving mobility by a factor of
3 compared to spin-coated devices
Pyridalthiadiazole-Based Narrow Band Gap Chromophores
Ď€-Conjugated materials containing pyridalÂ[2,1,3]Âthiadiazole
(PT) units have recently achieved record power conversion efficiencies
of 6.7% in solution-processed, molecular bulk-heterojunction (BHJ)
organic photovoltaics. Recognizing the importance of this new class
of molecular systems and with the aim of establishing a more concrete
path forward to predict improvements in desirable solid-state properties,
we set out to systematically alter the molecular framework and evaluate
structure–property relationships. Thus, the synthesis and properties
of 13 structurally related D<sup>1</sup>-PT-D<sup>2</sup>-PT-D<sup>1</sup> compounds, where D represents a relatively electron-rich
aromatic segment compared to PT, are provided. Physical properties
were examined using a combination of absorption spectroscopy, cyclic
voltammetry, thermal gravimetric analysis, differential scanning calorimetry,
and solubility analysis. Changes to end-capping D<sup>1</sup> units
allowed for fine control over electronic energy levels both in solution
and in the bulk. Substitution of different alkyl chains on D<sup>2</sup> gives rise to controllable melting and crystallization temperatures
and tailored solubility. Alterations to the core donor D<sup>2</sup> lead to readily identifiable changes in all properties studied.
Finally, the regiochemistry of the pyridal N-atom in the PT heterocycle
was investigated. The tailoring of structures via subtle structural
modifications in the presented molecular series highlights the simplicity
of accessing this chromophore architecture. Examination of the resulting
materials properties relevant for device fabrication sets forth which
can be readily predicted by consideration of molecular structure and
which lack a systematic understanding. Guidelines can be proposed
for the design of new molecular frameworks with the possibility of
outperforming the current state of the art OPV performance
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Optical Properties of Benzotriazole-Based Conjugated Polyelectrolytes
A series of conjugated polyelectrolytes
(CPEs) based on an electron-deficient
polybenzotriazole backbone with various pendant ionic functionalized
side chains were synthesized directly from the corresponding ionic
monomers. Of particular interest was to use the different chemical
structures to understand how the optical features are influenced by
the ionic side chains. We found that interchain aggregation is favored
in low dielectric constant solvents for cationic CPEs. Moreover, aggregated
species absorb at longer wavelengths and exhibit higher fluorescence
quantum yields
Gate-Tunable Electron Injection Based Organic Light-Emitting Diodes for Low-Cost and Low-Voltage Active Matrix Displays
Low-cost
and low-voltage active matrix displays were fabricated by simply patterning
gate electrode arrays on a polymer electrolyte (PE)-coated polymer
light-emitting diode (PLED). Structurally, a PE capacitor seamlessly
stacked on a PLED by sharing a common Al:LiF composite electrode (PEC|PLED).
This monolithic integrated organic optoelectronic device was characterized
and interpreted as the tunable work function (surface potential) because
of the perturbation of accumulated ions on Al:LiF composite electrode
by PEC charging and discharging. The modulation of electron injection
by the PEC resulted in increases in the electroluminescent brightness,
from <100 cd m<sup>–2</sup> to >8000 cd m<sup>–2</sup>, and the external quantum efficiency from <0.025% to 2.4%
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