Synthesis of Fully Soluble Azomethine-Bridged Ladder-Type Poly(p-phenylenes) by Bischler−Napieralski Reaction

Synthesis of Nitrogen-Doped Aza-Helicenes with Chiral Optical Properties

Aza-helicenes are one of the most important series of heterohelicenes; herein, a series of novel aza-helicenes (5H, 6H, 6S, and 8S) were prepared via Bischler-Napieralski cyclization, and the interconversion dynamic process of these aza-helicenes was revealed using density functional theory calculations. The novel nitrogen-doped [6]helicene (6H) possesses a very high interconversion energy barrier of 36.0 kcal/mol. Two enantiomers of 6H were successfully resolved by high-performance liquid chromatography and showed desired chiral optical properties. 6H with chiral optical activity and lone electrons can be a potential candidate for chiral switches, which was demonstrated using the UV and circular dichroism spectra obtained upon titration with an acid and a base.

Facile Synthesis of Solubilizing a Group-Free, Solution-Processable p-Type Ladder Conjugated Polymer and Its Thermoelectric Properties

Here we report the synthesis of a new solubilizing group-free, solution-processable p-type ladder conjugated polymer, 6H-pyrrolo[3,2-b:4,5-b']bis[1,4]benzothiazine ladder (PBBTL) polymer by using a polyphosphoric acid (PPA) and phenylphosphonic acid (PhPO₃H₂) 1:1 binary acid solvent system together with careful control of reaction kinetics. With a good intrinsic viscosity of 3.69 dL/g in methanesulfonic acid (MSA), good quality PBBTL films can be obtained via spin-coating. Intrinsic thin film properties and thermoelectric performance of PBBTL were evaluated, making it the second solubilizing group-free, solution-processable ladder-type conjugated polymer after BBL to be used for thin-film polymer electronics. While our preliminary thermoelectric performance of the FeCl₃-doped PBBTL films is modest, we believe that many opportunities lie ahead for PBBTL and hope that its successful synthesis using the new PPA:PhPO₃H₂ binary acid solvent system will inspire synthetic organic chemists to relook into solubilizing group-free, solution-processable ladder-type conjugated polymer systems.

Effective Synthesis of Ladder-type Oligo(p-aniline)s and Poly(p-aniline)s via Intramolecular SNAr Reaction

Symmetric ladder-type oligo(p-aniline)s and poly(p-aniline)s were successfully synthesized by an intramolecular ring closure in a highly efficient S_NAr reaction from oligo(p-phenylene)s and poly(p-phenylene)s with fluorine (F) and secondary amine (NH) groups. Unlike Cadogan ring closure, the newly designed cyclization reaction will not produce a mixture of symmetric and nonsymmetric structures. Moreover, the introduction of the F atom does not hinder Suzuki polymerization. The result indicates that preparing regular oligomers and polymers with a nitrogen bridge is possible.

Ladderization of polystyrene derivatives by palladium-catalyzed polymer direct arylation

Pseudo-ladderized polystyrenes could be obtained in high yield by the palladium-catalyzed polymer direct arylation using poly(2-bromostyrene) as a prepolymer.

Synthesis and Characterization of Fully Conjugated Ladder Naphthalene Bisimide Copolymers

Fully conjugated ladder copolymers have attracted considerable attention due to their unique fused-ring structure and optoelectronic properties. In this study, two fully conjugated ladder naphthalene diimide (NDI) copolymers, P(NDI-CZL) and P(NDI-TTL) with imine-bridged structures are presented in high yields. Both of the two copolymers have good solubility and high thermal stability. The corresponding compounds with the same structure as the copolymers were synthesized as model system. The yields for each step of the synthesis of the model compounds are higher than 95%. These results suggest that P(NDI-CZL) and P(NDI-TTL) can be synthesized successfully with fewer structural defects. The structures and optoelectronic properties of compounds and copolymers are investigated by NMR, fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis), and cyclic voltammetry (CV). Both in solution and as a thin film, the two copolymers show two UV-vis absorption bands (around 300⁻400 nm and 400⁻750 nm) and a very weak fluorescence. The collective results suggest that the two fully conjugated ladder copolymers can be used as potential acceptor materials.

Synthesis of Two Well-Defined Quadruple-Stranded Copolymers having Two Kinds of Backbones by Postpolymerization of a Helical Template Polymer

A brand new, soluble quadruple-stranded copolymer is synthesized by using a self-template polymer from a new monomer. In addition, another very unique quadruple-stranded copolymer having a π-π stacking supramolecular polymer main chain is synthesized by selective photocyclic aromatization of the quadruple-stranded copolymer. The two quadruple-stranded copolymers gave self-standing membranes.

Rigid-to-Flexible Conformational Transformation: An Efficient Route to Ring-Opening of a Tröger's Base-Containing Ladder Polymer

The synthesis of ladder polymers is still a big challenge in polymer chemistry, and in particular, there are few examples of conformationally flexible well-defined ladder polymers. Here we report an efficient and convenient route to conformationally flexible ladder polymers, which is based on a postpolymerization reaction of a rigid ladder polymer containing Tröger's base in its main chain. The postpolymerization reaction involves sequential N-methylation and hydrolysis for the Tröger's base unit, resulting in a diazacyclooctane skeleton that can exhibit a ring-flipping motion. Molecular dynamics simulations predicted that this motion provides conformational flexibility with the resultant ladder polymer, which was demonstrated by ¹H NMR spectroscopy in solution. The presence of the diazacyclooctane units in the flexible ladder polymer allowed further functionalization through reactions involving its secondary amine moiety. The present synthetic method may lead to the development of a new class of ladder polymers that exhibit both conformational and design flexibility.

Fully conjugated ladder polymers

Fully conjugated ladder polymers (cLPs), in which all the backbone units on the polymer main-chain are π-conjugated and fused, have attracted great interest owing to their intriguing properties, remarkable chemical and thermal stability, and potential suitability as functional organic materials. The synthesis of cLPs can be, in general, achieved by two main strategies: single-step ladderization and post-polymerization ladderization. Although a variety of synthetic methods have been developed, the chemistry of cLPs must contend with structural defects and low solubility that prevents complete control over synthesis and structural characterization. Despite these challenges, cLPs have been used for a wide range of applications such as organic light emitting diodes (OLEDs) and organic field effect transistors (OFETs), paralleling developments in processing methods. In this perspective, we discuss the background of historical syntheses including the most recent synthetic approaches, challenges related to the synthesis and structural characterization of well-defined cLPs with minimum levels of structural defects, cLPs' unique properties, and wide range of applications. In addition, we propose outlooks to overcome the challenges limiting the synthesis, analysis, and processing of cLPs in order to fully unlock the potential of this intriguing class of organic materials.

Influence of regiochemistry in the selective dispersion of metallic carbon nanotubes using electron poor conjugated polymers

Nitration of a poly(fluorene-co-phenylene) backbone influences its selectivity for semiconducting versus metallic single-walled carbon nanotubes, and the regiochemistry of the nitro group has a significant impact.

A radical addition/cyclization of diverse ethers to 2-isocyanobiaryls under mildly basic aqueous conditions

Addition of ethers and acetals to 2-isocyanobiaryls: a radical cascade promoted under mildly basic aqueous conditions.

Amide-bridged ladder poly(p-phenylene): synthesis by direct arylation and π-stacked assembly

Amide-bridged ladder poly(p-phenylene) was synthesized in two steps, through the polycondensation of aromatic diamines and dicarboxylic acid derivatives followed by palladium-catalyzed intramolecular direct arylation.