Unexpected twist to tweaking non-chiral polymers

A new study led by chemists at the University of Illinois at Urbana-Champaign brings fresh insight into the development of semiconductor materials that can do things their traditional silicon counterparts cannot – harness the power of chirality, a non-superimposable mirror image.

Chirality is one of the strategies that nature uses to build complexity into structures. The DNA double helix is perhaps the most recognized example of chirality – two molecule chains connected by a molecular ‘backbone’ and twisted to the right.

In nature, chiral molecules, like proteins, funnel electricity very efficiently by selectively transporting electrons of the same spin direction. Researchers have been working for decades to mimic nature’s chirality in synthetic molecules.

A new study, led by chemical and biomolecular chemistry professor Ying Diao, investigates how making various modifications to a non-chiral polymer called DPP-T4 can be used to form chiral helical structures in polymer-based semiconductor materials. Potential applications of this work include solar cells that function like leaves, computers that use quantum states of electrons to compute more efficiently and new imaging techniques that capture three-dimensional information rather than two-dimensional, to name a few. The chemists report their findings in a paper in ACS Central Science.

“We started by thinking that making small tweaks to the structure of the DPP-T4 molecule – achieved by adding or changing the atoms connected to the backbone – would alter the torsion, or twist of the structure, and induce chirality,” Diao said. “However, we quickly discovered that things were not that simple.”

Using X-ray scattering and imagining, the team found that their ‘slight tweaks’ caused major changes in the phases of the material.

“What we observed is a sort of Goldilocks effect,” Diao said. “Usually, the molecules assemble like a twisted wire, but suddenly, when we twist the molecule to a critical torsion, they started to assemble into new mesophases in the form of flat plates or sheets. By testing to see how well these structures could bend polarized light – a test for chirality – we were surprised to discover that the sheets can also twist into cohesive chiral structures.”

The team’s findings illustrate the fact that not all polymers will behave similarly when they are tweaked to mimic the efficient electron transport of chiral structures. The study demonstrates that it is critical not to overlook the formation of complex mesophase structures, which can lead to the discovery of unknown phases with previously unimagined optical, electronic and mechanical properties.

This story is adapted from material from the University of Illinois at Urbana-Champaign, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.