# Systematic C–C Bond Cleavage in Oligomers via Diels–Alder Reaction on Au(111)

## TL;DR

This paper shows how to break C–C bonds in carbon-based molecules on a gold surface using a chemical reaction, enabling controlled disassembly of complex structures.

## Contribution

The study introduces a method using the Diels–Alder reaction to lower the energy barrier for C–C bond cleavage in oligomers on Au(111).

## Key findings

- Fragmentation of tetra(9-anthryl)benzene oligomers was achieved via Diels–Alder reactions on Au(111).
- The Diels–Alder reaction significantly lowers the activation barrier for C–C bond cleavage.
- Combining scanning tunneling microscopy and DFT calculations revealed the fragmentation mechanism.

## Abstract

On-surface synthesis
became a powerful strategy to synthesize extended
nanocarbon materials, such as oligomers and graphene nanoribbons,
via C–C bond formation between small precursor molecules. However,
the reverse reaction, namely, C–C bond cleavage, remains challenging
due to the high activation barrier. Here, we present systematic fragmentation
to individual units from tetra­(9-anthryl)­benzene oligomers, which
were synthesized by Ullmann-type homocoupling on Au(111). The detailed
mechanism of fragmentation was investigated with a combination of
scanning tunneling microscopy and density functional theory calculations.
We found that the Diels–Alder reaction between anthracene groups
in the unit significantly lowers the activation barrier to cleave
the C–C bond between the units in the oligomer. Our findings
may offer an approach to disassemble oligomers in a controlled manner.