One eye on application – Charlotte Kress thrives at the intersection between classical disciplinesPortrait, SNI INSight May 2021
For her master’s thesis, Charlotte Kress synthesized a complex organic compound with potential applications in molecular electronics.
Bottom-up instead of top-down
Molecular electronics uses individual organic molecules, for instance as tiny switching elements in a circuit. In this bottom-up approach, larger electronic components are built from scratch using individual molecules, in contrast to the conventional top-down approach of progressively miniaturizing larger components.
Besides offering the researchers fundamental insights into how electricity is conducted at the atomic level, using individual molecules also allows them to explore the extent to which these minute but structurally diverse components can be used to customize certain electrical functions. These findings are of particular interest considering that conventional electronic components are approaching a point where further miniaturization will be impossible for various reasons.
Single molecules as electric conductors
Accordingly, for a number of years researchers in chemistry and physics have been working closely with each other to determine which molecules might be suitable for applications of this sort in electronic components.
Professor Michel Calame (Empa and the Department of Physics at the University of Basel) and his team have developed a technique whereby two individual molecules can be electrically connected between two tiny electrodes, allowing the researchers to investigate the molecules’ electric properties. The group led by Professor Marcel Mayor (Department of Chemistry, University of Basel) provides the molecules for these studies, a process that Charlotte Kress contributed to in the course of her award-winning master’s thesis.
Binding properties of sulfur and isocyanide
It has been known for some time that molecules possessing sulfur atoms as functional groups bind well to the gold electrodes used by Calame’s team. Another functional group that causes molecules to bind well to gold electrodes is isocyanide – in which a carbon atom is attached to a nitrogen atom by a triple bond.
The two teams, led by Marcel Mayor and Michel Calame, had previously succeeded in building one-dimensional chains between two gold electrodes from benzene rings with isocyanide groups.
In her master’s thesis project, Charlotte developed a macrocyclic – or ring-shaped – molecule in which an isocyanide group faces the center of the ring from both sides, thereby replicating the binding properties of the abovementioned one-dimensional chain in relation to gold atoms.
One step at a time
Charlotte spent the first few months of her master’s thesis project synthesizing the macrocyclic molecule in a number of steps. “To begin with, we put together a synthesis plan that worked quite well, and only required minor tweaking,” she explains. Her goal was to create two different molecules, one in which the isocyanide groups faced inward and another in which they faced outward.
In subsequent titration analyses, Charlotte found that the isocyanide groups bound very well to the gold atoms. The fact that the molecules are stable at room temperature and easy to store in powder form makes them promising candidates not just for applications in molecular electronics, but also as sensors for dissolved gold ions.
An eye on application
Charlotte found synthesizing organic materials to be thoroughly enjoyable. “That said, it is also important for me to have an application in sight – even if it is a long way off,” she adds. A particularly interesting aspect of this task for Charlotte was how it blurs the boundary between chemistry and physics.
Moreover, as she feels that she is in especially good hands in Mayor’s group, after completing her master’s Charlotte decided to proceed with a doctorate in the same field. To this end, she will continue her work with synthesis in a bid to produce molecules featuring isocyanide groups on both the inside and the outside. Her plan is to sandwich this macrocycle between two electrodes so as to replicate the proposed one-dimensional chain and confirm the accuracy of this hypothesis. Of course, as a determined chemist, she also plans to increase the yield, which currently stands at 7%, and subsequently characterize the new molecules in detail. Her focus here will also be on the molecules’ binding properties in relation to other materials of relevance to electronics besides gold atoms. She is particularly keen to see how her molecules perform in electronic tests in “field trials” by Calame’s team.
Focus on chemistry
Throughout her degree, Charlotte was always especially interested in topics involving two different disciplines. From the beginning, she was primarily interested in chemistry, but what really fascinated her was when a biological or physical aspect was added to the equation. A degree in nanosciences was therefore always going to be ideal.
The 25-year-old German, who grew up in Ticino, had her first brush with the nanosciences during her Matura (school-leaving certificate) project on the functionalization of nanoparticles. After earning her Matura, she felt the curriculum in Basel was a perfect fit, and has no regrets about embarking on a nanoscience degree in 2014.
“It wasn’t all plain sailing,” she remembers. “I really struggled with practical physics and the Physics III exam. In retrospect, however, I benefited immensely from many of these challenging subjects.” A highlight of the bachelor’s degree for Charlotte were the block courses and – as for so many of her fellow students – the fantastic team spirit among the nanoscience students.
“I hope to welcome many more colleagues of Charlotte’s caliber to my research group. Aside from her outstanding technical aptitude and unbridled scientific curiosity, what really sets her apart is her boundless enthusiasm and an inimitably cheerful nature that is contagious to everyone around her.”
Professor Marcel Mayor (Department of Chemistry, University of Basel)
Rewarding master’s degree
Overall, for Charlotte the master’s degree felt like “a reward for the bachelor’s”, allowing her to engage with a topic in greater detail and focus more on chemistry.
Before beginning her project assignments, Charlotte spent a semester doing a practical chemistry course for chemistry students in the 6th semester in preparation for her chemistry-related lab work. This gave her a solid foundation for her first project assignment at Osaka Prefecture University, involving the production and processing of a protein able to modify the functionalization of a carbon-carbon double bond.
Organic molecules were also the focus of Charlotte’s second project assignment – this time, those being studied by Professor Wenger’s team (University of Basel) for their applications in photovoltaics.
Throughout her nanoscience degree, Charlotte got to know numerous research groups, and over time she developed a keen sense for which topics particularly interested her. The affinity for chemistry that emerged during her school years remains as strong as ever, and she feels very much at home both in Mayor’s team and in the Department of Chemistry. Thanks to her nanoscience degree, however, she is also well equipped to understand the requirements of the physicists who will study her molecules for applications in electronics.