Tuneable near white-emissive two-dimensional covalent organic frameworks

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Two-dimensional covalent organic frameworks (2D COFs) often exhibit fluorescence quenching in the solid state.
• This quenching is typically due to non-radiative energy dissipation from molecular rotations or π-π stacking.
• A guiding principle for designing solid-state fluorescent COFs is currently lacking.

Purpose of the Study:

• To demonstrate a strategy for achieving solid-state photoluminescence in 2D COFs.
• To provide a design principle for creating tunable solid-state emitters based on COFs.
• To overcome the fluorescence quenching limitations in existing 2D COF materials.

Main Methods:

• Synthesized 2D COFs with an eclipsed stacking structure.
• Utilized intralayer and interlayer hydrogen bonds to restrict intramolecular bond rotation.
• Varied conjugated linker sizes and side-chain functionalities within the COF structure.

Main Results:

• Achieved solid-state photoluminescence from non-emissive building blocks in eclipsed-stacked 2D COFs.
• Demonstrated that the eclipsed stacking structure effectively restricts non-radiative decay pathways.
• Tuned the emission color from blue to yellow and white by modifying linker size and side chains.

Conclusions:

• The eclipsed stacking motif in 2D COFs is a viable strategy to achieve solid-state photoluminescence.
• Hydrogen bonding plays a crucial role in restricting molecular motion and enabling emission.
• This work offers a new platform and design guide for developing tunable solid-state emitters using COFs.