Better electronics: scientists get semiconductors to cooperate

For a long time, researchers have struggled to replicate the cooperative process found in viruses in non-living systems to reap their time- and energy-saving benefits. Diao and Daniel Davies, the study's lead author and a researcher at the Beckman Institute, decided to explore how molecular teamwork might impact the electronics sector.

"Molecular cooperativity helps living systems operate quickly and efficiently," Davies said. "We thought, 'If the molecules in electronic devices worked together, could those devices display those same benefits?'"

To test the outcome of such a collaboration, Diao and Davies studied organic electronic devices, which rely on semiconductors made from molecules like hydrogen and carbon rather than inorganic ones like silicon.

"Since organic electronics are made from the same basic elements as living beings, like people, they unlock many new possibilities for applications," said Diao.

 "In the future, organic electronics might be able to attach to our brains to enhance cognition or be worn like a Band-aid to convert our body heat into electricity."

A crucial step toward designing dynamic organic electronics like these is fashioning dynamic organic semiconductors. And for that to occur, the semiconductor molecules must collaborate.

An "avalanche"

The researchers discovered that rearranging the clusters of hydrogen and carbon atoms spooling out from a molecule's core — otherwise known as alkyl chains — causes the molecular core itself to tilt, triggering a crystal-wide chain of collapse the researchers refer to as an "avalanche."

On a scale much smaller than a plastic game piece, the researchers gradually applied heat to the molecule's alkyl chain, causing the crystal itself to shrink. In an electronic device, this property translates to an easy, temperature-induced on-off switch.

For now, the researchers have just achieved the first step of this collaboration, but they are nonetheless excited about the outcomes.

"The most exciting part was being able to observe how these molecules are changing and how their structure is evolving throughout these transitions," Davies said.

The study was published in Nature Communications.

Study abstract:

Cooperativity is used by living systems to circumvent energetic and entropic barriers to yield highly efficient molecular processes. Cooperative structural transitions involve the concerted displacement of molecules in a crystalline material, as opposed to typical molecule-by-molecule nucleation and growth mechanisms, which often break single crystallinity. Cooperative transitions have acquired much attention for low transition barriers, ultrafast kinetics, and structural reversibility. However, cooperative transitions are rare in molecular crystals, and their origin is poorly understood. Crystals of 2-dimensional quinoidal terthiophene (2DQTT-o-B), a high-performance n-type organic semiconductor, demonstrate two distinct thermally activated phase transitions following these mechanisms. Here we show reorientation of the alkyl side chains triggers cooperative behavior, tilting the molecules like dominos. Whereas nucleation and growth transition is coincident with increasing alkyl chain disorder and driven by forming a biradical state. We establish alkyl chain engineering as integral to rationally controlling these polymorphic behaviors for novel electronic applications.