On-Surface 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. Here, we report an 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.