On-surface synthesis of antiaromatic and open-shell indeno[2,1-b]fluorene polymers and their lateral fusion into porous ribbons

TL;DR

This paper reports the synthesis and characterization of antiaromatic, open-shell indeno[2,1-b]fluorene polymers on surfaces, revealing their electronic, magnetic, and structural properties relevant for organic electronics and spintronics.

Contribution

It introduces a novel on-surface synthesis method for antiaromatic, open-shell polymers and demonstrates their potential in electronics and magnetism studies.

Findings

Polymers exhibit low band gap on Au(111)

Lateral fusion creates porous ribbons with unique structures

Pronounced antiaromaticity and radical character confirmed by calculations

Abstract

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.