Energy portrait: Capturing a molecule's moment of excitement

A fundamental property of atoms and molecules is the energy at which electrons can be added to or removed from the compound. This is crucial for many chemical reactions where electrons are exchanged. Moreover, it holds significant potential for practical applications.

Organic compounds are promising candidates for advanced solar cells and light-emitting devices due to their affordability, abundance, and non-toxicity. For these devices to function effectively, the energies of electron exchange with the environment are of utmost importance.

The performance of solar cells and light-emitting devices is greatly influenced by excited states, where the molecule has absorbed extra energy. Knowing the value of this energy is essential for many applications.

Researchers at the University of Regensburg, in collaboration with IBM Research Europe—Zurich, have found a way to determine the energies of charge exchange for ground and excited states of a single molecule. They utilized an atomic force microscope, which detects tiny forces between a tip and a surface. This type of microscope can image the internal structure of single molecules, allowing researchers to identify the molecule under the microscope's tip.

Additionally, the tip can be used to locally add and remove electrons from the molecule. By slowly changing the energy of the electrons available in the tip and observing when the molecule undergoes charge-state transitions, the researchers were able to access and identify different excited states and measure their energies. They suggest that this technique could be applied to a wide range of molecules, both those of fundamental research interest and those relevant to energy conversion and organic electronics.

The study is published in the journal Nature Nanotechnology.

More information:
Lisanne Sellies et al, Controlled single-electron transfer enables time-resolved excited-state spectroscopy of individual molecules, Nature Nanotechnology (2024). DOI: 10.1038/s41565-024-01791-2

Provided by Universität Regensburg