Engineering single topological π-conjugated polymers and interpolating topological solitons by end-group modification

Topological solitons can act as mobile domain walls between topologically nontrivial and trivial phases, merging hybrid zero-mode properties from both solitonic and symmetry-protected boundary states, and providing both fundamental insights and unprecedented opportunities for quantum technologies. However, their experimental realization is challenging. Here, we demonstrate on-surface engineering of topological structures and introduction of topological solitons in π-conjugated pentacene polymers through end-group modification on Au(111), using combined multiple techniques including scanning tunneling microscopy, non-contact atomic force microscopy, and tip-enhanced Raman spectroscopy, along with density functional theory and tight-binding calculations. We fabricate cumulene-bridged pentacene oligomers and polymers with nearly length independence by anchoring their both termini to the surface. By converting a near-end segment into the trivial phase through its end group modification, we realize the interpolation of topological solitons as domain walls between nontrivial and trivial phases, which are well supported by observations of the solitonic zero-energy peaks across the domain walls, the band reverse between the separated regions, and the distinct region-dependent vibration modes, as well as theoretical calculations. The realization of topological solitons as domain walls between nontrivial and trivial phases offers a rich platform for fundamental research, and illustrates potential applications of π-conjugated polymers in quantum devices.