Covalently Scaffolded Inter‐π‐System Orientations in π‐Conjugated Polymers and Small Molecule Models

Organic π‐conjugated polymers have emerged as one of the most fascinating classes of materials as they have found utility in a host of plastic electronics technologies. The distance between π‐systems and their relative orientation dictate energy/charge transfer, conductivity, and photophysical properties of these materials in bulk. This Feature Article discusses π‐conjugated polymers and model compounds in which specific inter‐π‐system interactions are covalently enforced and the effect that the scaffolding has on optoelectronic properties.

     

Oligomerization of Electron‐Deficient Vinyl Monomers Through an Ate‐Complex Mechanism: A New Role for B(C6F5)3 Lewis Acid

The Lewis acid B(C₆F₅)₃ in combination with hydrosilanes exhibits remarkable activity in the oligomerization of sulfone‐ and phosphonate‐based monomers. This process opens new routes to high‐tech silicone‐based materials, i.e., thermoplastic elastomers and heat‐resistant polysiloxanes.

     

Construction of a Hexameric Zn(II)‐metallomacrocycle and its Photo‐ and Electroluminescence Properties: [Zn6(O‐hexyl‐3,5‐bis(2,2′:6′,2″‐terpyridine)phenol)6(BF4)12]

Summary: An O‐hexyl‐3,5‐bis(terpyridine)phenol ligand has been synthesized and transformed into a hexagonal Zn(II)‐metallomacrocycle by a facile self‐assembly procedure capitalizing on terpyridine‐Zn(II)‐terpyridine connectivity. The structural composition was confirmed by NMR and mass spectral techniques; photo‐ and electroluminescence properties were also investigated. The OLED device shows green electroluminescent emission at 515 nm with a maximum luminance of 39 cd · m⁻² and maximum efficiency of 0.16 cd · A⁻¹.

Structure and electroluminescent properties of the metallomacrocycle investigated.     

A New Concept for an Alkaline Developable Positive‐Tone Resist: Molecular Resist Utilizing Acid Catalyzed Isomerization from Oxabenzonorbornadiene to Naphthol

A novel positive‐tone molecular resist possessing oxabenzonorbornadiene moiety was developed for electron‐beam (EB) lithography. The synthesized resist material showed relatively high glass transition temperature and readily formed uniform amorphous films on a silicon wafer. The sensitivity of an EB resist was ca. 8 µC · cm⁻² and line and space patterns of 200 nm could be fabricated. The promising feature of the resist materials is that no outgassed products from base matrixes are theoretically produced under the exposure and post‐exposure bake procedure.

     

Highly Elastic and Deformable Hydrogel Formed from Tetra‐arm Polymers

After decades of efforts by many researchers, we have succeeded in realizing a near‐ideal polymer network. This network, the Tetra network, is made by cross‐end‐coupling of tetra‐arm polymer modules. The mechanical energy dissipation was extremely low (tan δ ≈ 10⁻⁴). The macroscopic stress–strain relationship of the Tetra network was in good agreement with that of microscopic elastic blobs. The maximum breaking strength was extremely high (≥27 MPa). These results indicate that the Tetra network is closer to an ideal polymer network than any other conventional model networks. Because the Tetra network can be treated as uniformly packed elastic blobs, it should help apply the knowledge of single polymer chains seamlessly to the design of polymer materials and help further develop the theory of rubber elasticity.

     

Post‐Synthesis Functionalization of (Meth)acrylate Based Monoliths via Electron Beam Triggered Graft Polymerization

Porous polymeric monoliths were prepared via electron beam triggered free radical polymerization of (meth)acrylates. Post‐synthesis functionalization of these supports was accomplished via electron beam initiated free radical graft polymerization of methacryloyl‐substituted NHC precursors. The grafted precursors were converted into the corresponding copper complexes. Cu‐loadings were between 1.3 mg · g⁻¹ and 1.5 mg · g⁻¹. These supported catalysts were used in selected CO hydrosilylation and cyanosilylation reactions using a continuous flow setup.

     

Preparation of Nanostructured Polyaniline and its Super‐Amphiphilic Behavior

PANI nanofibers are prepared electrochemically by template‐free method on a stainless steel electrode. Both the hydrophilicity and the lipophilicity of the modified SS surface are enhanced by the nanostructured PANI, and a super‐amphiphilic surface is obtained in this way. The influence of polymerization conditions, such as polymerization potentials, polymerization time, the acidity, and the dopants on the super‐amphiphilic property, has been systematically investigated. In addition, the mechanisms of obtaining a super‐amphiphilic surface are briefly discussed.

     

Transparent Nonlinear Optical Polymers for All‐Optical Wavelength Converters in Optical Fiber Communications

After synthesizing two chromophores with imine, we prepared acrylic nonlinear optical (NLO) polymers that contained the chromophores for all‐optical wavelength converters in optical fiber communication. The polymers show high d₃₃, 35 pm · V⁻¹, at 1.55 μm (pumping beam), considering their low losses, −3.0 dB · cm⁻¹, at a wavelength of 0.785 μm (near second harmonic signal beam of the pumping beam). This result means that the polymers are good candidates for wavelength converters of an approximately 1.55 μm signal beam.

UV‐vis spectra of NLO chromophores and polymers.     

Tunable Metal‐Enhanced Fluorescence by Stimuli‐Responsive Polyelectrolyte Interlayer Films

In this paper, we report on the tunable metal‐enhanced fluorescence (MEF) of Ag nanostructures. Because of the good MEF properties of the highly dendritic Ag nanostructures, we obtained an increase of up to 25 times for the weak fluorescence of porphyrin molecules (Por^4–). More importantly, by the introduction of a stimulus‐responsive PAA/PDDA multilayer film as an interlayer, the distance between the fluorophores and the Ag nanostructures could be tuned by immersing the substrates into solutions of different ionic strength or pH. The MEF behavior of the composite films could thus be tuned in a controlled manner, because of the distance dependent nature of the MEF effects.

     

Amphiphilic Invertible Polyesters as Reducing and Stabilizing Agents in the Formation of Metal Nanoparticles

Metal nanoparticles of various size and shape are prepared by the reduction of metal precursors in polymer micellar architectures (nanoreactors). The nanoreactors are developed from the amphiphilic invertible polyesters solved over a wide concentration range in solvents that strongly differ in polarity. In a non‐polar medium, the micelle core contains hydrophilic [poly(ethylene oxide)] fragments, which acts as a reducing agent of metal ions. Nanoparticle stabilization occurs because of the presence of hydrophobic (polymethylene) fragments outside of the micelle structure. The size and shape of the nanoreactors may be altered by the polyester composition and molecular weight as well as by the solvent polarity and concentration of the amphiphilic polyester.

     

Thin Films by Multilayer Build‐Up of Electron Transport Materials

We present the synthesis and the electrochemical characterization of polymeric electron transport materials, synthesized by polycondensation of substituted triazines and α,ω‐dihaloalkanes. They can be reversibly reduced with the least negative potential at −0.39 V, which is below the reduction potential of oxygen. In addition, the formation of polyelectrolyte multilayers is possible by the electrostatic self‐assembly method. This multilayer formation takes place in a very defined way up to thirty double layers.

An example of one of the polymeric triazine electron transport materials synthesized and a schematic diagram of a self‐assembled multilayer film.     

Synthesis of Cyclopentadienyl Capped Polyethylene and Subsequent Block Copolymer Formation Via Hetero Diels‐Alder (HDA) Chemistry

In the current contribution it is demonstrated – for the first time – that poly(ethylene) ( = 1 400 as well as 2 800 g · mol⁻¹, PDI = 1.2) can be readily equipped with highly reactive cyclopentadienyl (Cp) end groups. The Cp terminal poly(ethylene) can subsequently be reacted in an efficient hetero Diels‐Alder (HDA) reaction with macromolecules (poly(isobornyl acrylate) ( = 4 600 g · mol⁻¹, PDI = 1.10) and poly(styrene) ( = 6 300 g · mol⁻¹, PDI = 1.13) featuring strongly electron withdrawing thiocarbonyl thio end groups, prepared via reversible addition fragmentation chain transfer (RAFT) polymerization employing benzylpyridin‐2‐yldithioformate (BPDF) as transfer agent. The resulting block copolymers have been analyzed via high‐temperature size exclusion chromatography (SEC) as well as nuclear magnetic resonance (NMR) spectroscopy. The current system allows for the removal of the excess of the non‐poly(ethylene) containing segment via filtration of the poly(ethylene)‐containing block copolymer. However, the reaction temperatures need to be judiciously selected. Characterization of the generated block copolymers at elevated temperatures can lead – depending on the block copolymer type – to the occurrence of retro Diels‐Alder processes. The present study thus demonstrates that RAFT‐HDA ligation can be effectively employed for the generation of block copolymers containing poly(ethylene) segments.

     

Ethylene‐Norbornene Copolymerization by New Titanium Complexes Bearing Tridentate Ligands. Sidearm Effects on Catalytic Activity

The Ti complexes containing tridentate [O⁻NS^R] (R = Me, ⁱPr) ligands with alkylthio sidearms were prepared. The methylthio ether complex (R = Me shown in the Scheme) exhibits an excellent activity for copolymerization of ethylene with norbornene upon activation with MMAO, which is 10 times more active than the corresponding phenylthio one (R = Ph).