  Polycyclic hydrocarbons have received great attention due to their potential
role in organic electronics and, for open-shell systems with unpaired electron
densities, in spintronics and da-ta storage. However, the intrinsic instability
of polyradical hydrocarbons severely limits de-tailed investigations of their
electronic structure. Here, we report the on-surface synthesis of conjugated
polymers consisting of indeno[2,1-b]fluorene units, which are antiaromatic and
open-shell biradicaloids. The observed reaction products, which also include a
non-benzenoid porous ribbon arising from lateral fusion of unprotected
indeno[2,1-b]fluorene chains, have been characterized via low temperature
scanning tunneling microscopy/spectroscopy and non-contact atomic force
microscopy, complemented by density-functional theory calculations. These
polymers present a low band gap when adsorbed on Au(111). Moreover, their
pro-nounced antiaromaticity and radical character, elucidated by ab initio
calculations, make them promising candidates for applications in electronics
and spintronics. Further, they provide a rich playground to explore magnetism
in low-dimensional organic nanomaterials.
