Synthetic rings imitate plant energy systems with molecular precision

Synthetic rings imitate plant energy systems with molecular precision
by Riko Seibo
Tokyo, Japan (SPX) May 28, 2025

Plants have long inspired scientists with their remarkable ability to convert sunlight into energy through intricately organized pigment rings. Now, researchers at Osaka Metropolitan University have successfully emulated this architecture with synthetic molecules that self-assemble into stacked rings capable of energy and charge circulation, mimicking photosynthetic processes.

Photosynthetic organisms rely on ring-shaped pigment clusters to absorb sunlight effectively. These rings exhibit toroidal conjugation - a continuous circulation of energy and charge. Replicating this phenomenon could revolutionize solar cell design, but until now, artificial versions remained limited to isolated molecules.

"Artificial versions of toroidal conjugation have been limited to single molecules," explained Daisuke Sakamaki, associate professor at the university's Graduate School of Science and lead author of the study.

To overcome this limitation, the team developed a multi-molecule structure using phthalocyanines - planar aromatic compounds prevalent in dyes and photovoltaics. Each molecule features eight vertical, pillar-like extensions that facilitate electron transfer. These molecules self-assemble into interlocked pairs, ultimately forming a tightly packed, 16-layered ring. This configuration aligns molecular planes closely, enabling efficient energy and charge movement around the ring, akin to natural light-harvesting systems.

Structural integrity of the ring was verified through X-ray crystallography, while spectroscopic and theoretical analyses demonstrated active energy and charge circulation in both charged and excited states.

"This is the first clear evidence of intermolecular toroidal conjugation," Sakamaki stated. "Not only does this confirm that charge and energy can circulate in such assemblies, but it also reinvents how we think about using phthalocyanines - materials with more than a century of history."

The breakthrough highlights how simple molecular components, guided by self-assembly, can replicate nature's complex energy mechanisms. The research could lead to innovative applications in energy generation and optoelectronics.

"Our plan is to extend this approach to different types of molecules, aiming to design a wider variety of conjugated systems for future energy and optoelectronic applications," Sakamaki said.

Research Report:Intermolecular Toroidal Conjugation: Circularly Stacked 16 p-Planes Formed by Supramolecular Assembly Enabling Cyclic Charge and Energy Delocalization