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 m² g^–1. The porosity of the immobilized polymer is somewhat lower with a specific surface area of 123 m² g^–1

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 poly­(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-bis­(2-bromothien-5-yl)­naphthalene-1,4,5,8-tetracarboxylic-<i>N,N</i>′-bis­(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 poly­{[<i>N</i>,<i>N</i>′-bis­(2-octyldodecyl)-naphthalene-1,4,5,8-bis (dicarboximide)-2,6-diyl]-<i>alt</i>-5,5′-(2,2′-bithiophene)} (P­(NDI2OD-T2)) and its corresponding monomer 2,6-bis­(2-bromothien-5-yl)­naphthalene-1,4,5,8-tetracarboxylic-<i>N</i>,<i>N</i>′-bis­(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 P­(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>_1/2 = −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), P3­(EO)₃T-<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 P­(DPP2OD-T) (Poly­[[2,5-di­(2-octyldodecyl)­pyrrolo­[3,4-<i>c</i>]­pyrrole-1,4­(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 poly­(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 Ni­(dppp)­Cl₂ 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 Ni­(dppp)­Cl₂-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, P­(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 cm² V^–1 s^–1. Reduction of the active film thickness led to decreased <i>μ</i> values; however, FETs with ∼2 and ∼5 nm thick P­(NDI2OD-T2) films still exhibit substantial <i>μ</i>’s of 0.01–0.02 and ∼10^–4 cm² V^–1 s^–1, 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)­compensate for other effects