Non-covalent planarizing interactions yield highly ordered and thermotropic liquid crystalline conjugated polymers

Area of Science:

• Materials Science
• Polymer Chemistry
• Organic Electronics

Background:

• Controlling conjugated polymer morphology is key for organic electronics.
• Structural manipulation influences polymer assembly and properties.

Purpose of the Study:

• To report a redox-active conjugated polymer, TPT-TT, with intramolecular interactions.
• To investigate how these interactions affect main-chain planarity and solid-state order.
• To explore the resulting thermotropic liquid crystalline behavior and its impact on thin-film morphology and device performance.

Main Methods:

• Density functional theory (DFT) calculations to study intramolecular interactions.
• Cross-polarized optical microscopy (CPOM) and differential scanning calorimetry (DSC) to analyze thermotropic liquid crystalline behavior.
• Grazing-incidence X-ray diffraction (GIXD) to characterize thin-film long-range order.
• Fabrication and testing of organic field-effect transistors (OFETs).

Main Results:

• TPT-TT exhibits intramolecular S⋯O and S⋯H-C interactions promoting backbone planarization and temperature-dependent aggregation.
• Thermotropic liquid crystalline behavior (nematic and smectic A phases) was observed and characterized.
• Thermal annealing treatment resulted in highly ordered thin films with enhanced electrical conductivity (55 S cm⁻¹).
• Annealed films showed improved charge-carrier mobility (1.4 ± 0.1 × 10⁻² cm² V⁻¹ s⁻¹) and 100% OFET device yield.

Conclusions:

• Molecular design incorporating intramolecular interactions can control conjugated polymer solid-state order.
• Liquid crystallinity facilitates thermal annealing for enhanced morphology and electronic properties.
• This approach offers a pathway to high-performance organic electronic devices.