Hydrocarbon Frameworks with Long-Range Order Synthesized via Olefin Metathesis

Area of Science:

• Materials Science
• Polymer Chemistry
• Organic Chemistry

Background:

• Achieving long-range order in hydrocarbon covalent organic frameworks (COFs) is challenging due to irreversible carbon-carbon bond formation.
• Existing methods often lack effective error-correction mechanisms, limiting framework crystallinity.

Purpose of the Study:

• To demonstrate a molecular strategy for enhancing the crystallinity of hydrocarbon frameworks.
• To synthesize a highly ordered 2D COF using reversible reactions.

Main Methods:

• Synthesis of a 2D COF (HKU-50) using reversible olefin metathesis with a vinylene-bearing monomer and the second-generation Grubbs catalyst.
• Activation of secondary metathesis by adding trans-stilbene to regenerate trapped catalysts and enable continuous bond exchange.
• Utilizing the reversible nature of the reaction for in-situ error correction during framework formation.

Main Results:

• The system evolved towards a thermodynamically favored product, HKU-50, exhibiting long-range order.
• The resulting ordered COF demonstrated high thermal and chemical stability.
• Enhanced photophysical properties were observed, including red-shifted emission, prolonged fluorescence lifetime, and a four-fold increase in photoluminescence quantum yield compared to amorphous analogues.

Conclusions:

• A molecular approach successfully controlled the crystallinity of hydrocarbon frameworks via reversible olefin metathesis.
• This method enables continuous error correction during synthesis, leading to improved material order and properties.
• The findings offer a new pathway for designing ordered hydrocarbon COFs without relying on external ordering agents.