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Scientists at the Institute of Organic Chemistry, University of Vienna, have unveiled an innovative approach for synthesizing azaparacyclophanes (APCs), a class of highly advanced ring-shaped molecular structures with immense potential in material science.

Their innovative Catalyst-Transfer Macrocyclization (CTM) method, in JACS Au, streamlines the production of these complex macrocycles, paving the way for more efficient and scalable applications in organic electronics, optoelectronics, and supramolecular chemistry—such as displays, flexible solar cells and transistors.

APCs are small, perfectly shaped molecular rings made up of repeating units linked in an endless loop. These macrocyclic organic compounds have a unique structure that makes them valuable basic building blocks for innovative technologies such as optoelectronic applications.

For years, the synthesis of APCs has been a tedious process requiring several steps under difficult conditions. A team of researchers at the Institute of Organic Chemistry at the University of Vienna has taken on the challenge to simplify it—with remarkable success.

A shortcut to complex molecular rings

The newly developed CTM method uses the "Pd-catalyzed Buchwald-Hartwig cross-coupling reaction," which helps to form carbon-nitrogen bonds to create π-conjugated cyclic structures. "π-conjugated" refers to a system of alternating single and double bonds that allows the free movement of electrons, enhancing the electronic properties of the material. The CTM method provides a direct and efficient route, making the production of APCs much easier.

"With this approach, we can create structurally precise APCs in a short time, under mild conditions and with high yields, making them much more accessible for both research and industrial applications," says first author Josue Ayuso-Carrillo from the University of Vienna.

The method is flexible, allowing the preparation of APCs with different ring sizes (typically 4–9 members) and functional groups. It can also be carried out under typical concentration conditions (35–350 mM), making it scalable and reproducible, unlike established macrocyclization protocols requiring a highly diluted medium.

A game changer for advanced technologies

APCs produced by this method have great potential in materials such as organic semiconductors and solar technology. Thanks to their π-conjugated structures, which allow efficient electron movement, APCs can be used in various fields.

In organic electronics, they can improve the efficiency and flexibility of displays, solar cells and transistors. Organic electronics contain—as the name suggests—organic material. This goes for flexible solar cells, for example.

Compared to typical flat panels of solar cells made of energy-intensive processed silicon, organic solar cells are lightweight, and hence can be used off-grid in unconventional surfaces. APCs' properties also improve light-harvesting systems, leading to better solutions for solar energy conversion and storage.

In supramolecular chemistry, APCs can also be used to create advanced molecular recognition systems, sensors and catalysts. "The CTM method is not only a breakthrough in synthesis, but also a stepping stone towards the large-scale production of tailor-made materials," explains Davide Bonifazi from the University of Vienna, senior author of the study.

"By eliminating unnecessary complexity, we open the door to new functional applications that were previously out of reach. And, importantly, we demonstrate the reproducibility of our method by providing a step-by-step guide for researchers in related fields."