Molecule Suggested in 1902 Gets its First Close-Up

Today, chemistry teachers and students can breath a sigh of relief. After teaching and learning about a particular family of molecules for decades, scientists have finally proven that they do in fact exist.

AFM image of an aryne molecule imaged with a CO tip
In a new paper published online today in Nature Chemistry, scientists from IBM Research and CIQUS at the University of Santiago de Compostela, Spain, have confirmed the existence and characterized the structure of arynes (pronounced "ärēən"), a family of highly-reactive short-lived molecules which was first suggested 113 years ago. The technique has broad applications for on-surface chemistry and electronics, including the preparation of graphene nanoribbons and novel single-molecule devices.

“Arynes are discussed in almost every undergraduate course on organic chemistry around the world. Therefore, it’s kind of a relief to find the final confirmation that these molecules truly exist,” said Prof. Diego Peña, a chemist at the University of Santiago de Compostela.

“I look forward to seeing new chemical challenges solved by the combination of organic synthesis and atomic force microscopy."

There are trillions of molecules in the universe and some of them are stable enough to be isolated and characterized, but many others are so short-lived that they can only be proposed indirectly, via chemical reactions or spectroscopic methods.

One such species are arynes, which were first suggested in 1902, and since then have been used as intermediates or building blocks in the synthesis of a variety of compounds for applications including medicine, organic electronics and molecular materials. The challenge with these particular molecules is that they only exist for several milliseconds making them extremely challenging to image, until now.

The imaging was accomplished by means of atomic force microscopy (AFM), a scanning technique that can accomplish nanometer-level resolution. After the preparation of the key aryne precursor by CIQUS, IBM scientists used the sharp tip of a scanning tunneling microscope (STM) to generate individual aryne molecules from precursor molecules by atomic manipulation. The experiments were performed on films of sodium chloride, at temperatures near absolute zero, to stabilize the aryne.

Once the molecules were isolated, the team used AFM to measure the tiny forces between the STM tip, which is terminated with a single carbon monoxide molecule, and the sample to image the aryne’s molecular structure. The resulting image was so clear that the scientists could study their chemical nature based on the minute differences between individual bonds.

“Our team has developed several state-of-the-art techniques since 2009, which made this achievement possible,” said Dr. Niko Pavliček, a physicist at IBM Research - Zurich and lead author of the paper. “For this study, it was absolutely essential to pick an insulating film on which the molecules were adsorbed and to deliberately choose the atomic tip-terminations to probe them. We hope this technique will have profound effects on the future of chemistry and electronics."

Prof. Peña, added that "These findings on arynes can be compared with the long-standing search for the giant squid. For centuries, fishermen had found clues of the existence of this legendary animal. But it was only very recently that scientists managed to film a giant squid alive. In both cases, state-of-the-art technologies were crucial to observe these elusive species alive: a low-noise submarine for the giant squid; a low-temperature AFM for the aryne."

This research is part of IBM’s five-year, $3 billion investment to push the limits of chip technology and semiconductor innovations needed to meet the emerging demands of cloud computing and Big Data systems.

This work is a result of the large European project called (Planar Atomic and Molecular Scale Devices). PAMS’ main objective is to develop and investigate novel electronic devices of nanometric-scale size. Part of this research is also funded by a European Research Council Advanced Grant awarded to IBM scientist Gerhard Meyer, who is also a co-author of the paper.

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