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

Topological solitons can act as mobile domain walls between topologically non-trivial 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 both their 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 non-trivial 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 non-trivial and trivial phases offers a rich platform for fundamental research, and illustrates potential applications of π-conjugated polymers in quantum devices.