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1. Highly fluorescent purine-containing conjugated copolymers with tailored optoelectronic properties

   https://doi.org/10.1039/D2PY00545J  

   O'Connell, C. Elizabeth; Sabury, Sina; Jenkins, J. Elias; Collier, Graham S.; Sumpter, Bobby G.; Long, Brian K.; Kilbey, S. Michael (August 2022, Polymer Chemistry)

   Conjugated copolymers containing electron donor and acceptor units in their main chain have emerged as promising materials for organic electronic devices due to their tunable optoelectronic properties. Herein, we describe the use of direct arylation polymerization to create a series of fully π-conjugated copolymers containing the highly tailorable purine scaffold as a key design element. To create efficient coupling sites, dihalopurines are flanked by alkylthiophenes to create a monomer that is readily copolymerized with a variety of conjugated comonomers, ranging from electron-donating 3,4-dihydro-2 H -thieno[3,4- b ][1,4]dioxepine to electron-accepting 4,7-bis(5-bromo-3-hexylthiophen-2-yl)benzo[ c ][1,2,5]thiadiazole. The comonomer choice and electronic nature of the purine scaffold allow the photophysical properties of the purine-containing copolymers to be widely varied, with optical bandgaps ranging from 1.96–2.46 eV, and photoluminescent quantum yields as high as ϕ = 0.61. Frontier orbital energy levels determined for the various copolymers using density functional theory tight binding calculations track with experimental results, and the geometric structures of the alkylthiophene-flanked purine monomer and its copolymer are found to be nearly planar. The utility of direct arylation polymerization and intrinsic tailorability of the purine scaffold highlight the potential of these fully conjugated polymers to establish structure–property relationships based on connectivity pattern and comonomer type, which may broadly inform efforts to advance purine-containing conjugated copolymers for various applications. 

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2. Diversifying peripheral aromatic units of pyrrolo[3,2- b ]pyrrole-containing conjugated polymers and the resulting optoelectronic properties

   https://doi.org/10.1039/D5TC00292C  

   Collier, Graham S; Layton, Julien T; Skiouris, Perry; Bell, Kenneth-John J; Wagner, Ethan W; Phan, Vanessa; Fraser, Sarah G; Tomlinson, Aimée L (May 2025, Journal of Materials Chemistry C)

   Pyrrolo[3,2-b]pyrrole represents a synthetically-simple conjugated scaffold that enables accessing polymers with tailorable properties useful for organic electronics. 

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3. Relating Design and Optoelectronic Properties of 1,4-Dihydropyrrolo[3,2- b ]pyrroles Bearing Biphenyl Substituents

   https://doi.org/10.1021/acs.jpcb.3c03061  

   Hawks, Allison M.; Altman, Drake; Faddis, Ryan; Wagner, Ethan M.; Bell, Kenneth-John J.; Charland-Martin, Ariane; Collier, Graham S. (July 2023, The Journal of Physical Chemistry B)

   Understanding the influence of peripheral functionality on optoelectronic properties of conjugated materials is an important task for the continued development of chromophores for myriad applications. Here, π-extended 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) chromophores with varying electron-donating or electron-withdrawing capabilities were synthesized via Suzuki cross-coupling reactions, and the influence of functionality on optoelectronic properties was elucidated. First, chromophores display distinct differences in the UV–vis absorbance spectra measured via UV–vis absorbance spectroscopy in addition to changes in the onset of oxidation measured with cyclic voltammetry and differential pulse voltammetry. Solution oxidation studies found that variations in the electron-donating and -withdrawing capabilities result in different absorbance profiles of the radical cations that correspond to quantifiably different colors. In addition to fundamental insights into the molecular design of DHPP chromophores and their optoelectronic properties, two chromophores display high-contrast electrochromism, which makes them potentially compelling in electronic devices. Overall, this study represents the ability to fine-tune the optoelectronic properties of DHPP chromophores in their neutral and oxidized states and expands the understanding of structure–property relationships that will guide the continued development of DHPP-based materials. 

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4. Azomethine‐Containing Pyrrolo[3,2‐ b ]pyrrole Copolymers for Simple and Degradable Conjugated Polymers

   https://doi.org/10.1002/marc.202300220  

   Bartlett, Kimberley A.; Charland‐Martin, Ariane; Lawton, Jonathan; Tomlinson, Aimée L.; Collier, Graham S. (July 2023, Macromolecular Rapid Communications)

   Abstract Conjugated polymers have received significant attention as potentially lightweight and highly tailorable alternatives to inorganic semiconductors, but their synthesis is often complex, produces toxic byproducts, and they are not typically designed to be degradable or recyclable. These drawbacks necessitate dedicated efforts to discover materials with design motifs that enable targeted and efficient degradation of conjugated polymers. In this vein, the synthetic simplicity of 1,4‐dihydropyrrolo[3,2‐ b ]pyrroles (DHPPs) is exploited to access azomethine‐containing copolymers via a benign acid‐catalyzed polycondensation protocol. Polymerizations involve reacting a dialdehyde‐functionalized dihydropyrrolopyrrole with p ‐phenylenediamine as the comonomer using p ‐toluenesulfonic acid as a catalyst. The inherent dynamic equilibrium of the azomethine bonds subsequently enabled the degradation of the polymers in solution in the presence of acid. Degradation of the polymers is monitored via NMR, UV‐vis absorbance, and fluorescence spectroscopies, and the polymers are shown to be fully degradable. Notably, while absorbance measurements reveal a continued shift to higher energies with extended exposure to acid, fluorescence measurements show a substantial increase in the fluorescence response upon degradation. Results from this study encourage the continued development of environmentally‐conscious polymerizations to attain polymeric materials with useful properties while simultaneously creating polymers with structural handles for end‐of‐life management or/and recyclability. 

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5. Relating Structure to Properties in Non‐Conjugated Pendant Electroactive Polymers

   https://doi.org/10.1002/marc.202300219  

   Schmitt, Alexander; Thompson, Barry C. (July 2023, Macromolecular Rapid Communications)

   Abstract Non‐conjugated pendant electroactive polymers (NCPEPs) are an emerging class of polymers that offer the potential of combining the desirable optoelectronic properties of conjugated polymers with the superior synthetic methodologies and stability of traditional non‐conjugated polymers. Despite an increasing number of studies focused on NCPEPs, particularly on understanding fundamental structure‐property relationships, no attempts have been made to provide an overview on established relationships to date. This review showcases selected reports on NCPEP homopolymers and copolymers that demonstrate how optical, electronic, and physical properties of the polymers are affected by tuning of key structural variables such as the chemical structure of the polymer backbone, molecular weight, tacticity, spacer length, the nature of the pendant group, and in the case of copolymers the ratios between different comonomers and between individual polymer blocks. Correlation of structural features with improved π ‐stacking and enhanced charge carrier mobility serve as the primary figures of merit in evaluating impact on NCPEP properties. While this review is not intended to serve as a comprehensive summary of all reports on tuning of structural parameters in NCPEPs, it highlights relevant established structure‐property relationships that can serve as a guideline for more targeted design of novel NCPEPs in the future. 

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