By using on-surface synthesis, we present a chemical reaction based on the regio- and stereoselective coupling of indenyl moieties for fabricating π-conjugated acenoindenylidene polymers, which feature a longitudinal polyacetylene backbone, on a Au(111) surface. The relationship between structural parity and electronic properties is investigated. We discover that odd-membered polymers exhibit an in-gap soliton state, which, due to their low bandgaps, spatially extends several nanometres along the longitudinal polyacetylene backbone. To read more...