Electronic polymers are chains of molecules that conduct electricity. These polymers need a clear path for electrons to travel along the entire polymer. Ring-shaped components have different electron transport pathways than linear components. Now, scientists have created a new type of conducting polymer containing both linear and ring elements. Every other link in this polymer contains a ring hanging from the polymer chain, similar to how charms hang from a dangling bracelet. The new polymers have very different electronic properties than scientists would expect if the polymers simply added the contributions from each linear and ring-shaped component. These new polymers create opportunities for scientists to design new materials with useful electronic properties.
Electronic polymers can coat large and complex surfaces at low temperatures and at low cost. This gives them advantages over other types of electronic materials. The novel combination of linear and ring-shaped molecules creates a new type of conducting polymer. This discovery opens new possibilities for moving energy within and between polymers. It also offers new design opportunities for applications including displays, light sources, solar cells, and sensors.
Scientists use the concept of molecular orbitals to describe the location and behavior of a molecule’s electrons. Ring-shaped molecular structures, called cycloparaphenylenes (CPPs), have overlapping molecular orbitals that enable electrons to migrate around the ring. This property is affected by the number of molecular units referred to as arylenes that make up the ring. Researchers synthesized CPPs with 6 or 8 arylene units and linked them together to form linear polymers. These polymers incorporate the rings at regular intervals along the linear conducting polymer backbone. In this new configuration, electrons can travel along the linear polymer and also around the CPP rings. Absorption spectra showed that these structures created new electronic states. Importantly, these states are not simply additive for the ring structures plus the conducting polymer backbone. Scientists confirmed this result by characterizing electronic properties using photoluminescence studies. The researchers also conducted computational studies to further understand the orbital overlaps, the effective lengths of these overlaps, and the electronic properties. The hybrid structures with both linear and ring-shaped features created new states that enabled electrons to move freely through the polymer. These materials have intriguing electronic properties, and the research provides guidance for the design of new organic electronic materials.
This highlight is based upon work supported by the Department of Energy Office of Science, Office of Basic Energy Sciences. In addition, one of the researchers was supported by the National Science Foundation Graduate Research Fellowship.