Rational Monomer Design for the Synthesis of Conjugated Polymers by Direct Heteroarylation Polymerization

Area of Science:

• Organic Chemistry
• Materials Science
• Polymer Chemistry

Background:

• Direct heteroarylation polymerization is a key method for synthesizing conjugated polymers.
• Monomer design significantly influences reactivity and polymerization outcomes.
• Electron-deficient cores are crucial for tuning electronic properties and enabling C-H activation.

Purpose of the Study:

• To investigate the design principles for C-H activation in bithiophene-flanked monomers.
• To correlate monomer structure with reactivity for direct heteroarylation polymerization.
• To explore the synthesis of novel polymers incorporating naphthalene diimide (NDI), perylene diimide (PDI), and fluorene (FLU) units.

Main Methods:

• Density functional theory (DFT) calculations to determine energy requirements for C-H bond abstraction.
• Proton NMR spectroscopy to experimentally validate predicted reactivity profiles.
• Direct heteroarylation polymerization to synthesize target polymers.

Main Results:

• DFT calculations revealed that the electron-withdrawing strength of the central aromatic core (NDI, PDI, FLU) dictates C-H bond activation energy.
• NDI- and PDI-flanked monomers showed lower energy requirements for C-H activation compared to fluorene-flanked monomers.
• Experimental results confirmed the DFT predictions, with successful polymerization achieved for NDI and PDI monomers.

Conclusions:

• Monomer design, specifically the choice of electron-deficient core, is critical for efficient C-H activation in direct heteroarylation.
• NDI and PDI are suitable building blocks for direct heteroarylation polymerization due to favorable energy profiles.
• Fluorene-based monomers present challenges for this polymerization method owing to higher energy demands for C-H activation.