Crystallization of Dimensional Isomers in Covalent Organic Frameworks

Area of Science:

• Materials Science
• Chemistry
• Reticular Chemistry

Background:

• Dimensional isomers in reticular chemistry involve identical building blocks forming 2D or 3D frameworks.
• These isomers have been theoretically proposed but never experimentally isolated.
• Covalent organic frameworks (COFs) are crystalline porous polymers with tunable structures.

Purpose of the Study:

• To achieve the first experimental crystallization of dimensional isomers in reticular materials.
• To investigate the role of precursor conformation in forming different dimensionalities.
• To explore the conversion and property changes between dimensional isomers.

Main Methods:

• Synthesizing covalent organic frameworks (COFs) using identical molecular building blocks under varying temperatures.
• Utilizing solvothermal conditions to induce conformational changes in precursors (planar to tetrahedral).
• Characterizing the resulting 2D and 3D COF structures and their properties, including fluorescence.

Main Results:

• Successfully crystallized both 2D and 3D dimensional isomers of COFs from the same precursors.
• Demonstrated that temperature control dictates the dimensionality of the COF structures.
• Showed that a non-fluorescent 2D COF can be converted to a fluorescent 3D COF by increasing temperature.

Conclusions:

• The conformation of molecular building blocks is a key factor for crystallizing dimensional isomers in reticular materials.
• This work provides a viable strategy for designing and synthesizing dimensional isomers.
• The ability to interconvert isomers with different properties opens avenues for developing advanced functional materials.