In this record we provide data to support our recent work on the synthesis of oligo(indenoindene). Fully conjugated ladder polymers (CLP) possess unique optical and electronic properties and are considered promising materials for applications in (opto)electronic devices. Poly(indenoindene) is a CLP consisting of an alternating array of five- and six-membered rings, which has remained elusive so far. Our results relate to on-surface synthesis of oligo(indenoindene) on Au(111). Its structure and a low electronic band gap have been elucidated by low-temperature scanning tunneling microscopy and spectroscopy and noncontact atomic force microscopy, complemented by density functional theory calculations. Achieving defect-free segments of oligo(indenoindene) offers exclusive insight into this CLP and provides the basis to further synthetic approaches.