12 research outputs found
Surface-Initiated Synthesis of Conjugated Microporous Polymers: Chain-Growth Kumada Catalyst-Transfer Polycondensation at Work
Most of conjugated microporous polymers (CMPs) prepared
to date
are poorly processable, intractable solids. The immobilization of
CMPs onto various surfaces is strongly desirable for many applications,
such as for gas storage and separation, heterogeneous catalysis, and
so forth. However, the preparation of thin porous films remains a
challenging task. This Letter reports Ni-catalyzed surface-initiated
Kumada catalyst-transfer polycondensation of a tetrafunctional thiophene-based
(AB) 2-monomer from organosilica microparticles leading to microparticles
covered by thin-film (∼30 nm) layers of the CMP. A sample of
unbound CMP was also prepared by a bulk polymerization of the same
monomer. Thus-obtained CMP possesses a relatively high specific surface
area of 463 m<sup>2</sup> g<sup>–1</sup>. The porosity of the
immobilized polymer is somewhat lower with a specific surface area
of 123 m<sup>2</sup> g<sup>–1</sup>
Fullerene-Functionalized Donor–Acceptor Block Copolymers through Etherification as Stabilizers for Bulk Heterojunction Solar Cells
A new synthetic method for the covalent linking of fullerenes
to
polymers is introduced. The Bingel-reaction was used to prepare bromine-functionalized
fullerene building blocks that could be covalently linked to hydroxyl
groups of model copolymers by the cesium carbonate promoted Williamson
ether synthesis. Subsequently, block copolymers with a second block
based on styrene and hydroxystyrene or hydroxyethyl methacrylate could
be synthesized with a polyÂ(3-hexylthiophene)–TEMPO macroinitiator
through NMRP. Fullerene derivatives were linked to these polymers
in a controlled manner and donor–acceptor block copolymers
with high fullerene contents of near 50 wt % were achieved
Mechanistic Insight into Catalyst-Transfer Polymerization of Unusual Anion-Radical Naphthalene Diimide Monomers: An Observation of Ni(0) Intermediates
Ni-catalyzed polymerization of anion-radical complexes
formed upon mixing of 2,6-bisÂ(2-bromothien-5-yl)Ânaphthalene-1,4,5,8-tetracarboxylic-<i>N,N</i>′-bisÂ(2-octyldodecyl) diimide and activated Zn
powder was investigated. We provide experimental evidence that the
polymerization involves the chain-growth mechanism and proceeds via
Ni(0) complexes which were previously proposed to be key intermediates
in other chain-growth catalyst-transfer polycondensations (CTPs),
such as Kumada CTP of thiophenic monomers. DFT calculations predict
a remarkable stability of the naphthalene diimide-based Ni(0) complexes.
A plausible polymerization mechanism is proposed
Electrochemical Investigations of the N‑Type Semiconducting Polymer P(NDI2OD-T2) and Its Monomer: New Insights in the Reduction Behavior
This
manuscript provides the first systematic characterization
of the electrochemical properties of the high mobility n-type polymer
polyÂ{[<i>N</i>,<i>N</i>′-bisÂ(2-octyldodecyl)-naphthalene-1,4,5,8-bis
(dicarboximide)-2,6-diyl]-<i>alt</i>-5,5′-(2,2′-bithiophene)}
(PÂ(NDI2OD-T2)) and its corresponding monomer 2,6-bisÂ(2-bromothien-5-yl)Ânaphthalene-1,4,5,8-tetracarboxylic-<i>N</i>,<i>N</i>′-bisÂ(2-octyldodecyl) diimide
(Br-NDI2OD-T2-Br) by cyclic voltammetry and in situ spectroelectrochemistry.
Both monomer and polymer reveal a 2-fold reduction to the dianion
via a radical anion species. The comparison between monomeric and
polymeric species allows the explanation of the electrochemical behavior
of PÂ(NDI2OD-T2) according to redox polymers with localization of charges
on the naphthalene bisimide unit. Measurements with electrolyte gated
transistors suggest electron hopping transport according to mixed
valence conductivity. In the last section of this paper we discuss
a significant first cycle effect upon electrochemical reduction which
had not been reported for n-type polymers before. The effect is even
more pronounced for samples with controlled morphology, that is, high
amounts of aggregation in the films. In agreement with solution experiments
we attribute the appearance of the signal at −1.04 V (<i>E</i><sub>1/2</sub> = −1.00 V) to the radical anion form
of the solvated species
High Triplet Energy Polymers Containing Phosphine Oxide as Novel Hosts for Solution-Processable Organic Light-Emitting Diodes
Semiconducting
polymers enable the fabrication of low-cost, large-area
electronic devices by using low-temperature solution-processing methodologies
on flexible substrates. This work presents three novel host materials
for the emitting layer (EML) of organic light-emitting diodes (OLEDs).
Efficient hosts should possess a number of properties, such as high
triplet energy, good and balanced charge-carrier transport, suitable
frontier orbital levels that match those of the neighboring layers,
and morphological stability. To this end, carbazole-based polymers
featuring the electron-withdrawing group (EWG) phenylphosphine oxide
at different positions of the chain were designed and synthesized
by Suzuki coupling. Chemical and optical characterizations of the
polymers were performed prior to the charge-transport property analysis
through the fabrication of single-carrier devices. Finally, these
materials were incorporated into a green OLED architecture as solution
processed EML where tris(2-phenylpyridine)iridium(III) (Ir(ppy)3) acts as phosphorescent emitter dopant
Tunable Fluorescence of a Semiconducting Polythiophene Positioned on DNA Origami
A novel
approach for the integration of π-conjugated polymers
(CPs) into DNA-based nanostructures is presented. Using the controlled
Kumada catalyst-transfer polycondensation, well-defined thiophene-based
polymers with controllable molecular weight, specific end groups,
and water-soluble oligoethylene glycol-based side chains were synthesized.
The end groups were used for the easy but highly efficient click chemistry-based
attachment of end-functionalized oligodeoxynucleotides (ODNs) with
predesigned sequences. As demonstrated by surface plasmon resonance
spectroscopy, the prepared block copolymers (BCPs), P3Â(EO)<sub>3</sub>T-<i>b</i>-ODN, comprising different ODN lengths and specific
or repetitive sequences, undergo specific hybridization with complementary,
thiol-functionalized ODNs immobilized on a gold surface. Furthermore,
the site-specific attachment of the BCPs to DNA origami structures
is studied. We demonstrate that a nanoscale object, that is, a single
BCP with a single ODN handle, can be directed and bound to the DNA
origami with reasonable yield, site-specificity, and high spatial
density. On the basis of these results, we are able to demonstrate
for the first time that optical properties of CP molecules densely
immobilized on DNA origami can be locally fine-tuned by controlling
the attractive π–π-stacking interactions between
the CPs. In particular, we show that the fluorescence of the immobilized
CP molecules can be significantly enhanced by surfactant-induced breakup
of π–π-stacking interactions between the CP’s
backbones. Such molecular control over the emission intensity of the
CPs can be valuable for the construction of sophisticated switchable
nanophotonic devices and nanoscale biosensors
One-Pot Synthesis of All-Conjugated Block-Like Bisthiophene–Naphthalenediimide/Fluorene Copolymer
A copolymerization of electron-rich
and electron-deficient monomers
via the chain-growth catalyst-transfer polycondensation route is highly
challenging and has never been accomplished thus far, to the best
of our knowledge. Herein, we report a simple method to copolymerize
two monomers of a significantly different nature: anion-radical naphthalene
diimide–dithiophene-based and zinc-organic AB-type fluorenic
ones. We found that the copolymerization proceeds rapidly in the presence
of Pd catalyst having the bulky and electron-rich tri<i>-tert</i>-butylphosphine ligand. Despite the fact that the two monomers are
simultaneously added to the copolymerization (batch polymerization),
the polymerization leads to a gradient or even block-like copolymer
rather than to a random copolymer or to a mixture of homopolymers,
as evident from NMR, GPC, AFM, and fluorescence quenching experiments.
The block-like copolymer is formed because the fluorenic monomer polymerizes
much faster, yet because the resulting PF2/6 homopolymer is able to
initiate polymerization of the second monomer, presumably acting as
macroinitiator. Although the investigated copolymerization does not
involve a living propagation mechanism and the resulting product is
not a well-defined block copolymer, this result is an important step
toward a general protocol for preparation of all-conjugated donor–acceptor
block copolymers for optoelectronic applications
Synthesis of High-Crystallinity DPP Polymers with Balanced Electron and Hole Mobility
We review the Stille coupling synthesis
of PÂ(DPP2OD-T) (PolyÂ[[2,5-diÂ(2-octyldodecyl)ÂpyrroloÂ[3,4-<i>c</i>]Âpyrrole-1,4Â(2<i>H</i>,5<i>H</i>)-dione-3,6-diyl]-<i>alt</i>-[2,2′:5′,2″-terthiophene-5,5″-diyl]])
and show that high-quality, high molecular weight polymer chains are
already obtained after as little as 15 min of reaction time. The results
of UV–vis spectroscopy, grazing incidence wide-angle X-ray
scattering (GIWAXS), and atomic force microscopy show that longer
reaction times are unnecessary and do not produce any improvement
in film quality. We achieve the best charge transport properties with
polymer batches obtained from short reaction times and demonstrate
that the catalyst washing step is responsible for the introduction
of charge-trapping sites for both holes and electrons. These trap
sites decrease the charge injection efficiency, strongly reducing
the measured currents. The careful tuning of the synthesis allows
us to reduce the reaction time by more than 100 times, achieving a
more environmentally friendly, less costly process that leads to high
and balanced hole and electron transport, the latter being the best
reported for an isotropic, spin-coated DPP polymer
On the Role of Single Regiodefects and Polydispersity in Regioregular Poly(3-hexylthiophene): Defect Distribution, Synthesis of Defect-Free Chains, and a Simple Model for the Determination of Crystallinity
Identifying structure formation in semicrystalline conjugated
polymers
is the fundamental basis to understand electronic processes in these
materials. Although correlations between physical properties, structure
formation, and device parameters of regioregular, semicrystalline
polyÂ(3-hexylthiophene) (P3HT) have been established, it has remained
difficult to disentangle the influence of regioregularity, polydispersity,
and molecular weight. Here we show that the most commonly used synthetic
protocol for the synthesis of P3HT, the living Kumada catalyst transfer polycondensation (KCTP) with
NiÂ(dppp)ÂCl<sub>2</sub> as the catalyst, leads to regioregular chains
with one single tail-to-tail (TT) defect distributed over the whole
chain, in contrast to the hitherto assumed exclusive location at the
chain end. NMR end-group analysis and simulations are used to quantify
this effect. A series of entirely defect-free P3HT materials with
different molecular weights is synthesized via new, soluble nickel
initiators. Data on structure formation in defect-free P3HT, as elucidated
by various calorimetric and scattering experiments, allow the development
of a simple model for estimating the degree of crystallinity. We find
very good agreement for predicted and experimentally determined degrees
of crystallinities as high as ∼70%. For NiÂ(dppp)ÂCl<sub>2</sub>-initiated chains comprising one distributed TT unit, the comparison
of simulated crystallinities with calorimetric and optical measurements
strongly suggests incorporation of the TT unit into the crystal lattice,
which is accompanied by an increase in backbone torsion. Polydispersity
is identified as a major parameter determining crystallinity within
the molecular weight range investigated. We believe that the presented
approach and results not only contribute to understanding structure
formation in P3HT but are generally applicable to other semicrystalline
conjugated polymers as well
Influence of Semiconductor Thickness and Molecular Weight on the Charge Transport of a Naphthalenediimide-Based Copolymer in Thin-Film Transistors
The
N-type semiconducting polymer, PÂ(NDI2OD-T2), with different molecular
weights (MW = 23, 72, and 250 kg/mol) was used for the fabrication
of field-effect transistors (FETs) with different semiconductor layer
thicknesses. FETs with semiconductor layer thicknesses from ∼15
to 50 nm exhibit similar electron mobilities (<i>μ</i>’s) of 0.2–0.45 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. Reduction of the active film thickness led
to decreased <i>μ</i> values; however, FETs with ∼2
and ∼5 nm thick PÂ(NDI2OD-T2) films still exhibit substantial <i>μ</i>’s of 0.01–0.02 and ∼10<sup>–4</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, respectively. Interestingly, the lowest molecular weight sample
(P-23, MW ≈ 23 kg/mol, polydispersity index (PDI) = 1.9) exhibited
higher <i>μ</i> than the highest molecular weight
sample (P-250, MW ≈ 250 kg/mol, PDI = 2.3) measured for thicker
devices (15–50 nm). This is rather unusual behavior because
typically charge carrier mobility increases with MW where improved
grain-to-grain connectivity usually enhances transport events. We
attribute this result to the high crystallinity of the lowest MW sample,
as confirmed by differential scanning calorimetry and X-ray diffraction
studies, which may (over)Âcompensate for other effects