On-surface radical ring-opening polymerization produces ultralong poly(para-phenylene) for access to non-benzenoid carbon nanoribbons.

Extending the chain lengths of conductive polymers, such as unsubstituted poly(para-phenylene) (PPP), is crucial for their application in high-performance organic devices and processing into high-quality functional materials. While surface-assisted Ullmann coupling has increased PPP chain lengths to ~100 nm, from ~32 nm achieved by solution-based reactions, its step-growth reaction mechanism limits further elongation. Here we report the synthesis of PPP via radical ring-opening polymerization of [6]cyclo(para-phenylene) on a Cu(111) surface. This process has been identified as a chain-growth polymerization, substantially enhancing the PPP chain length to the micrometre range (~0.9 μm). The obtained ultralong PPP chains on an otherwise clean surface undergo selective C-H bond scission, forming an upright-standing poly(para-benzyne) intermediate, which further couples into the unsubstituted biphenylene ribbon with length up to ~40 nm. The ring-opening polymerization provides a versatile route to high-quality polymers and non-benzenoid carbon nanoribbons with precise structural control.