On-surface synthesis enables soliton states for odd-membered polymers

A new on-surface chemical reaction enables the appearance of solitons in π-conjugated polymers. The reaction, called indenyl coupling, reveals that structural parity drives the appearance of solitons in odd-membered π conjugated polymers. The results are a collaboration among scientists at IMDEA Nanociencia, CiQUS (Spain) and the Czech Academy of Science.

The findings are published in the journal Nature Synthesis.

π-conjugated polymers are a class of macromolecules featuring an alternation of single and double bonds along their backbone, which enables delocalized π-electrons. Their unique electronic structure makes them highly conductive and very attractive for applications such as solar cells or light-emitting diodes.

To enhance their electronic properties, π-conjugated polymers are often doped. However, the structure and stability of the polymer suffers.

In their study, researchers introduced a chemical reaction, coined indenyl coupling, to design highly conducting polymers. They demonstrated the possibility of bonding indane-based monomers in an extremely selective and efficient way on a metallic surface, enabling the design of π-conjugated polymers.

Remarkably, the researchers exploited the structural parity of the polymers to enable the emergence of in-gap soliton states, which spatially extend several nanometers along the longitudinal backbone.

The results answer a fundamental question in materials science: Is it possible to experimentally synthetize potentially highly conducting polymers without the need for external doping?

The authors demonstrate via scanning probe microscopy experiments that theoretical predicted concepts of structural parity can be an essential factor to consider when designing tailored nanomaterials hosting topological quasiparticles. This approach could lead to more efficient, cost-effective, and sustainable electronic devices featuring 1D wires.