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Subtle Molecular Changes Largely Modulate Chiral Helical Assemblies of Achiral Conjugated Polymers by Tuning
Kyung Sun Park1, Xuyi Luo2, Justin J Kwok3
1Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 S. Mathews Ave., Urbana, Illinois 61801, United States.
ACS Central Science
|November 30, 2023
Summary
Researchers explored how conjugated polymer structures in solution affect their hierarchical assembly and chiral properties. They found that aggregate dimensionality significantly influences helical assembly, paving the way for advanced chiral optoelectronics.
Area of Science:
- Materials Science
- Polymer Chemistry
- Organic Electronics
Background:
- Controlling the multiscale morphologies and electronic properties of conjugated polymers in solid thin films requires understanding their solution-state aggregate structures.
- Detailed comprehension of these solution aggregate structures, especially their chiral assembly, is challenging due to complex aggregation behaviors.
Purpose of the Study:
- To investigate the solution-state aggregate structures of achiral diketopyrrolopyrrole-quaterthiophene (DPP-T4) copolymer and its analogues (DPP-T2M2, DPP-T2F2).
- To elucidate the impact of these aggregate structures on hierarchical chiral helical assembly.
- To correlate aggregate dimensionality with chiral helical pitch and optoelectronic properties.
Main Methods:
- Small-angle X-ray scattering (SAXS) analysis.
- Microscopic solution imaging techniques.
- Synthesis and characterization of DPP-T4, DPP-T2M2, and DPP-T2F2 copolymers.
Main Results:
- Distinct aggregate structures were identified: DPP-T2F2 formed semicrystalline 1D fiber aggregates with strong internal binding, DPP-T2M2 formed semicrystalline 1D fiber aggregates with weak internal binding, and DPP-T4 formed highly crystalline 2D sheet aggregates.
- These aggregates formed lyotropic chiral helical liquid crystal (LC) mesophases at high concentrations.
- Aggregate dimensionality modulated helical pitches, with 2D sheets yielding larger pitches than 1D fibers.
- DPP-T2F2 exhibited a high anisotropic dissymmetry factor (g-factor) of 0.09 due to its ordered 1D fiber aggregates and small helical pitch.
Conclusions:
- The dimensionality of solution aggregates is a key factor in controlling the hierarchical chiral helical assembly of conjugated polymers.
- This understanding enables the rational design of chiral organic semiconductors for emerging chiral optoelectronics.
- The study provides significant insights into the solution-state hierarchical and chiral assembly of achiral organic semiconductors.
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