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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.
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Using molecular straps to engineer conjugated porous polymer growth, chemical doping, and conductivity
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.
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- Award ID(s):
- 1944184
- PAR ID:
- 10500350
- Publisher / Repository:
- Chemical Science
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 14
- Issue:
- 20
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 5510 to 5518
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D3SC00983A
