An official website of the United States government
Abstract In the past decade, direct arylation polymerization (DArP) has rapidly developed as a sustainable synthetic protocol for cost‐effective, atom‐economical preparation of conjugated polymers. By circumventing monomer functionalization with toxic transmetallating reagents such as organostannane and organoboron required for Stille‐Migita and Suzuki‐Miyaura polymerization methods, DArP proceeds through a metal‐catalyzed CH activation pathway for the preparation of high‐performance conjugated polymer materials. This review evaluates the development of several classes of efficient catalysts/catalytic systems from small‐molecule studies to polymerizations, including the mechanisms involved in these transformations and how they inspire catalyst and monomer design for defect‐free conjugated polymer synthesis. Recent advances in developing more sustainable first‐row transition metal catalysts for DArP are also highlighted, and the fundamental understanding of these efficient and sustainable catalysts should motivate the pursuit for the next generation of catalytic design to enable more effective and environmentally friendly conjugated polymer synthesis.
more »
« less
Multicomponent Polymerization for π‐Conjugated Polymers
Abstract Structurally complex π‐conjugated polymers hold great promise as key components in sensor and electronic devices; however, their syntheses have not been a trivial task. From a synthetic efficiency perspective, it would be more attractive to access these materials using convenient and efficient methods from simple building blocks. One such synthetic tool, multicomponent polymerization, can accommodate modularity and provide highly efficient syntheses. This feature article outlines several multicomponent polymerization strategies for the synthesis of various π‐conjugated polymers, which are classified based upon how the monomers are aligned during polymerization. Additionally, the challenges and outlooks of this field are highlighted and discussed.
more »
« less
- PAR ID:
- 10452601
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Macromolecular Rapid Communications
- Volume:
- 42
- Issue:
- 6
- ISSN:
- 1022-1336
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Pyrazinacenes are next generation N-heteroacenes and represent a novel class of stable n-type materials capable of accepting more than one electron and displaying intriguing features, including prototropism, halochromism, and redox chromism. Astonishingly, despite a century since their discovery, there have been no reports on the conjugated polymers of pyrazinacenes due to unknown substrate scope and lack of pyrazinacene monomers that are conducive to condensation polymerization. Breaking through these challenges, in this work, we report the synthesis of previously undiscovered and highly coveted conjugated polymers of pyrazinacenes. In order to understand the intricacies of conjugation extension within the acene and along the polymer backbone, a series of electronically diverse four pyrazinacene conjugated polymers were synthesized. Polymers synthesis required optimizing a few synthetic steps along the 12-step synthetic pathway. The generated pyrazinacene monomers are not amenable to the popular condensation polymerizations involving Pd or Cu catalysts. Gratifyingly, Pd and Cu free dehydrohalogenation polymerization of the monomer with HgCl2 resulted in high molecular weight organometallic conjugated pyrazinacene polymers within a few minutes at room temperature. The dual role played by the Hg(II) during the polymerization, combined with the self-coupling of the RHgCl (intermediate), is at the core of successful polymerization. Notably, the self-coupling of intermediates challenges the strict stoichiometric balance typically required for step-growth polymerization and offers a novel synthetic strategy to generate high molecular weight conjugated polymers even with imbalanced monomer stoichiometries. A combination of electrochemical studies and DFT-B3LYP simulations indicated that the presence of the reduced pyrazine ring promotes interacene p-conjugation through the metal center, in contrast to completely oxidized tetrazaazaanthracene. The extension of conjugation results in ca. 2 eV lower reduction potential for polymers compared to the monomer, placing the LUMO energy levels of these polymers on par with some of the best-known n-type polymers. Also, the presence of NH protons in the pyrazinacene polymers show ionochromism and red-shift UV-vis absorption maximum by ca. 100 nm. This work not only shows a way to realize highly desirable and elusive pyrazinacene conjugated polymers but also paves the way for a library of n-type conjugated polymers that can undergo multi-electron reduction.more » « less
-
Abstract Mechanically deformable polymeric semiconductors are a key material for fabricating flexible organic thin‐film transistors (FOTFTs)—the building block of electronic circuits and wearable electronic devices. However, for many π‐conjugated polymers achieving mechanical deformability and efficient charge transport remains challenging. Here the effects of polymer backbone bending stiffness and film microstructure on mechanical flexibility and charge transport are investigated via experimental and computational methods for a series of electron‐transporting naphthalene diimide (NDI) polymers having differing extents of π‐conjugation. The results show that replacing increasing amounts of the π‐conjugated comonomer dithienylvinylene (TVT) with the π‐nonconjugated comonomer dithienylethane (TET) in the backbone of the fully π‐conjugated polymeric semiconductor, PNDI‐TVT100(yielding polymeric series PNDI‐TVTx, 100 ≥x≥ 0), lowers backbone rigidity, degree of texturing, and π–π stacking interactions between NDI moieties. Importantly, this comonomer substitution increases the mechanical robustness of PNDI‐TVTxwhile retaining efficient charge transport. Thus, reducing the TVT content of PNDI‐TVTxsuppresses film crack formation and dramatically stabilizes the field‐effect electron mobility upon bending (e.g., 2 mm over 2000 bending cycles). This work provides a route to tune π–π stacking in π‐conjugated polymers while simultaneously promoting mechanical flexibility and retaining good carrier mobility in FOTFTs.more » « less
-
Thin films of poly(arylene ethynylene) conjugated polymers, including low-energy-gap donor–acceptor polymers, can be prepared via stepwise polymerization utilizing surface-confined Sonogashira cross-coupling. This robust and efficient polymerization protocol yields conjugated polymers with a precise molecular structure and with nanometer-level control of the organization and the uniform alignment of the macromolecular chains in the densely packed film. In addition to high stability and predictable and well-defined molecular organization and morphology, the surface-confined conjugated polymer chains experience significant interchain electronic interactions, resulting in dominating intermolecular π-electron delocalization which is primarily responsible for the electronic and spectroscopic properties of polymer films. The fluorescent films demonstrate remarkable performance in chemosensing applications, showing a turn-off fluorescent response on the sub-ppt (part per trillion) level of nitroaromatic explosives in water. This unique sensitivity is likely related to the enhanced exciton mobility in the uniformly aligned and structurally monodisperse polymer films.more » « less
-
Abstract Synthetic helical polymers form compact, ordered, and inherently chiral structures, enabling their uses in biomimetic applications as well as catalysis. A challenge in using synthetic helical polymers, however, is their tendency to be sensitive to pH and the presence of nucleophiles, Lewis‐acids, or metal ions. We report a strategy to overcome these shortcomings by adapting catalyst‐transfer polymerization, a living chain‐growth polymerization typically used to access linear conjugated polymers, for the synthesis of helical poly(thiophene)s. We demonstrate that the helical poly(thiophene)s can be synthesized with a single helicity, incorporated into block copolymers, and functionalized at the chain‐ends, enabling further conjugation and functionalization. The helical poly(thiophene)s are stable to a variety of conditions, providing benefits over other helical polymers which contain sensitive imine or carbonyl‐based functional groups. We anticipate that the ability to access homochiral, heterotelechelic helical conjugated polymers and copolymers will enable new uses of these materials in optoelectronics as well as in applications for mimicking biomacromolecules and other polymers with precisely defined sequences.more » « less
