An official website of the United States government
π-Conjugated polymers that extend the π-conjugation in more than one dimension are highly sought after for various organic electronic and energy applications. However, the synthesis of solution processable higher dimensional π-conjugated materials is still at its infancy because of strong interchain π–π interactions. The conventional strategy of using linear alkyl pendant chains does not help overcome the strong interchain π–π interactions in higher dimensional π-conjugated materials as they do not directly mask the π-face of the repeat units. While the miniemulsion technique has been employed to generate hyperbranched π-conjugated polymer particles stabilized by surfactants, this approach does not address the molecular level challenges. We have proposed that π-face masking straps mask the π-face of the polymer backbone and therefore help to control π–π interchain interactions in higher dimensional π-conjugated materials at the molecular level. Herein, we have shown that when a strapped aryl dialdehyde monomer (A2) is reacted with a trifunctional 1,3,5-benzenetriamine (B3) using dynamic imine chemistry, a solution dispersible and processable hyperbranched polymer with a degree of branching of 0.46 is generated. Also, by varying the reaction conditions (catalyst, monomer concentration, and solvent), solution dispersible polymer particles of varying diameters ranging from 60 to 300 nm are generated. It is worth noting that despite having the suitable monomer architectures for the formation of ordered frameworks, a hyperbranched polymer is generated because the straps effectively hinder interlayer π–π stacking interactions, thereby preventing the formation of crystalline aggregates that are required for the growth of the former. Since straps stabilize the chains against π–π interactions at the molecular level, they will not only provide synthetic control over the architecture but also remove typical synthetic limitations associated with the miniemulsion technique including functional group intolerance and monomer miscibility.
more »
« less
This content will become publicly available on November 19, 2025
Advancements in π-conjugated polymers: harnessing cycloalkyl straps for high-performance π-conjugated materials
Pendant alkyl chains are widely used to successfully obtain a wide variety of soluble linear 1D π-conjugated polymers. Over the past several decades, a wide variety of π-conjugated polymers have been synthesized to realize the desired properties and improve the performance of organic electronic devices. However, this strategy is not suitable for generating soluble 2D-π-conjugated materials, including ladder polymers, nanoribbons, and 2D-π-conjugated polymers, due to strong van der Waals interactions between the ribbons and sheets. The drive to synthesize higher dimensional polymers and to enhance polymers' properties has spurred the exploration of a novel direction in materials chemistry—the synthesis of unconventional monomers and polymers. The Gavvalapalli research group has developed and used cycloalkyl straps containing aryl building blocks for the synthesis of conjugated polymers. These cycloalkyl straps, positioned either above or below the π-conjugation plane, have been shown to directly control the π–π interactions between the polymer chains. We have demonstrated that π-face masking cycloalkyl straps hinder interchain π–π interactions. The first part of this review article highlights the use of cycloalkyl straps for the synthesis of higher dimensional π-conjugated polymers. In this section, we discuss the synthesis of 2D-H-mers, dispersible hyperbranched π-conjugated polymers, and conjugated porous polymers without the pendant solubilizing chains. The second part of the feature article highlights how the cycloalkyl straps can be used to gain control over polymer–acceptor interactions, including the interaction strength and the location of the acceptor along the polymer backbone. We conclude the article with the future outlook on cycloalkyl strap-containing building blocks in the world of conjugated polymers.
more »
« less
- Award ID(s):
- 1944184
- PAR ID:
- 10630031
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- Chemical Communications
- Volume:
- 60
- Issue:
- 93
- ISSN:
- 1359-7345
- Page Range / eLocation ID:
- 13653 to 13666
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Controlling network growth and architecture of 3D-conjugated porous polymers (CPPs) is challenging and therefore has limited the ability to systematically tune the network architecture and study its impact on doping efficiency and conductivity. We have proposed that π-face masking straps mask the π-face of the polymer backbone and therefore help to control π–π interchain interactions in higher dimensional π-conjugated materials unlike the conventional linear alkyl pendant solubilizing chains that are incapable of masking the π-face. Herein, we used cycloaraliphane-based π-face masking strapped monomers and show that the strapped repeat units, unlike the conventional monomers, help to overcome the strong interchain π–π interactions, extend network residence time, tune network growth, and increase chemical doping and conductivity in 3D-conjugated porous polymers. The straps doubled the network crosslinking density, which resulted in 18 times higher chemical doping efficiency compared to the control non-strapped-CPP. The straps also provided synthetic tunability and generated CPPs of varying network size, crosslinking density, dispersibility limit, and chemical doping efficiency by changing the knot to strut ratio. For the first time, we have shown that the processability issue of CPPs can be overcome by blending them with insulating commodity polymers. The blending of CPPs with poly(methylmethacrylate) (PMMA) has enabled them to be processed into thin films for conductivity measurements. The conductivity of strapped-CPPs is three orders of magnitude higher than that of the poly(phenyleneethynylene) porous network.more » « less
-
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
-
null (Ed.)Understanding the structural parameters that determine the extension of π-conjugation in 2-dimensions is key for controlling the optical, photophysical, and electronic properties of 2D-π-conjugated materials. In this article, three non-slanted H-mers including a donor–acceptor H-mer (H-mer-3) with an increase in dihedral angle (twist) between the strands and rungs are synthesized and studied. These non-slanted H-mers represent the repeat units of 2D-π-conjugated materials. H-mer-3, containing donor-strands and an acceptor-rung, is an unexplored donor–acceptor architecture in both slanted and non-slanted H-mers. The H-mers displayed both acid and base dependent optical properties. While the rungs have a little impact on the H-mer absorption spectra they play a key role in the emission and fluorescence lifetime. H-mer-3 ( i.e. , donor–acceptor H-mer) shows a higher Stokes shift and fluorescence lifetime than the other two H-mers. The twist and the presence of an electron deficient rung in H-mer-3 facilitated an intramolecular charge transfer in the excited state from the strands to the electron deficient rung, and therefore control over the H-mer emission properties. The lack of insulating pendant chains, reduced π–π interactions in thinfilms, and longer fluorescence lifetimes make these H-mers interesting candidates for various electronic and optoelectronic applications.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
