Extending on-surface synthesis from 2D to 3D by cycloaddition with C₆₀

Area of Science:

• Materials Science
• Organic Chemistry
• Surface Science

Background:

• On-surface synthesis (OSS) enables sub-molecular level investigation of intermolecular coupling and polymer formation.
• Current OSS methods are limited to two-dimensional lateral covalent bonding within a single molecular layer.
• Extending OSS to three-dimensional synthesis remains a significant challenge in molecular engineering.

Purpose of the Study:

• To develop a novel on-surface synthesis strategy for creating three-dimensional covalently-bonded organic architectures.
• To explore the perpendicular covalent coupling of fullerene (C60) with aromatic compounds on surfaces.
• To enable precise bottom-up synthesis of complex 3D organic structures for potential device applications.

Main Methods:

• Assembly of a C60 layer on a well-defined molecular network to facilitate molecular orbital hybridization.
• Thermal activation to induce [4+2] cycloaddition between C60 and phenyl rings, forming perpendicular covalent bonds.
• Characterization of the resulting adducts, including their orientation and sub-molecular features at room temperature.

Main Results:

• Successful realization of perpendicular covalent coupling between C60 and aromatic molecules on a surface via [4+2] cycloaddition.
• The resulting adducts exhibited frozen orientation and distinct sub-molecular features at room temperature.
• Demonstrated subsequent lateral covalent bonding via [2+2] cycloaddition, enabling further structural extension.

Conclusions:

• This study presents an unconventional route for the precise bottom-up synthesis of 3D covalently-bonded organic architectures on surfaces.
• The developed method overcomes the limitations of 2D OSS, opening new possibilities for constructing complex 3D molecular structures.
• The findings pave the way for novel 3D organic materials and devices fabricated through surface-confined synthesis.