Subtle Molecular Changes Largely Modulate Chiral Helical Assemblies of Achiral Conjugated Polymers by Tuning Solution-State Aggregation

Journal Article · Mon Nov 13 00:00:00 EST 2023 · ACS Central Science

DOI:https://doi.org/10.1021/acscentsci.3c00775· OSTI ID:2470096

Park, Kyung Sun ^[1]; Luo, Xuyi ^[2]; Kwok, Justin J. ^[1]; Khasbaatar, Azzaya ^[1]; Mei, Jianguo ^[2]; Diao, Ying ^[1]

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1. Univ. of Illinois at Urbana-Champaign, IL (United States)
2. Purdue Univ., West Lafayette, IN (United States)

Understanding the solution-state aggregate structure and the consequent hierarchical assembly of conjugated polymers is crucial for controlling multiscale morphologies during solid thin-film deposition and the resultant electronic properties. However, it remains challenging to comprehend detailed solution aggregate structures of conjugated polymers, let alone their chiral assembly due to the complex aggregation behavior. Herein, we present solution-state aggregate structures and their impact on hierarchical chiral helical assembly using an achiral diketopyrrolopyrrole-quaterthiophene (DPP-T4) copolymer and its two close structural analogues wherein the bithiophene is functionalized with methyl groups (DPP-T2M2) or fluorine atoms (DPP-T2F2). Combining in-depth small-angle X-ray scattering analysis with various microscopic solution imaging techniques, we find distinct aggregate in each DPP solution: (i) semicrystalline 1D fiber aggregates of DPP-T2F2 with a strongly bound internal structure, (ii) semicrystalline 1D fiber aggregates of DPP-T2M2 with a weakly bound internal structure, and (iii) highly crystalline 2D sheet aggregates of DPP-T4. These nanoscopic aggregates develop into lyotropic chiral helical liquid crystal (LC) mesophases at high solution concentrations. Intriguingly, the dimensionality of solution aggregates largely modulates hierarchical chiral helical pitches across nanoscopic to micrometer scales, with the more rigid 2D sheet aggregate of DPP-T4 creating much larger pitch length than the more flexible 1D fiber aggregates. Combining relatively small helical pitch with long-range order, the striped twist-bent mesophase of DPP-T2F2 composed of highly ordered, more rigid 1D fiber aggregate exhibits an anisotropic dissymmetry factor (g-factor) as high as 0.09. This study can be a prominent addition to our knowledge on a solution-state hierarchical assembly of conjugated polymers and, in particular, chiral helical assembly of achiral organic semiconductors that can catalyze an emerging field of chiral (opto)electronics.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
• Sponsoring Organization: National Science Foundation (NSF); US Air Force Office of Scientific Research (AFOSR); US Office of Naval Research (ONR); USDOE Office of Science (SC)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 2470096
• Journal Information: ACS Central Science, Journal Name: ACS Central Science Journal Issue: 11 Vol. 9; ISSN 2374-7943
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Chemistry
conjugated polymers
differential pulse voltammetry
fibers
mesostructures
polymer solutions