Systematic C-C Bond Cleavage in Oligomers via Diels-Alder Reaction on Au(111).

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.