On-surface synthesis of covalently bonded molecular structures on insulators
Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
Final Report Abstract
In retrospect, the original goal of synthesizing large covalent structures on an insulator was too ambitious to be conducted within the framework of a single PhD work. However, the intermediate steps towards this final goal turned out to offer several highly interesting research paths on their own. We studied in detail the bond cleavage at ether moieties within individual molecules. The phenoxy moiety breaks off selectively at the oxygen position, leaving behind the radicalic core of the respective molecule. For this study different species were investigated ranging from phthalocyanine cores over carbines to quinodimethane derivatives. While the bond cleavage worked in all cases reliably, the short carbine derivatives could be split up by injecting only one or few electrons into the lowest unoccupied molecular orbital of the molecule. In the case of the phthalocyanine derivative the radicalic nature of the core after bond cleavage could be directly visualized in corresponding force microscopy images and is reflected in the electronic properties as revealed by means of scanning tunneling spectroscopy and imaging. The possibility of the bond cleavage that occurs selectively at particular bonds and subsequent atomic characterization in terms of bond order and electronic properties provides access to the intriguing competition between aromatic closed-shell and other biradical forms. We followed two other routes to activate molecules on insulators. We successfully coupled laser light into the junction and could thereby generate single-electron photocurrents that could be detected by means of force microscopy. Apart from its potential to induce reactions this research opens novel research paths that will be followed in the future. Finally, on thick insulators we induced electronically-excited states by suitable sequences of voltage pulses in single molecules and studied the decay. Specifically, we excited the model system pentacene to triplet states. We could measure the lifetime decay of these triplet states in different local environments. These experiments open up the general perspective to study out-ofequilibrium states in single-molecules at atomic scales and in the time domain.
Publications
- Atomically resolved single-molecule triplet quenching. Science 373, 452 (2021)
J. Peng, S. Sokolov, D. Hernangómez-Pérez, F. Evers, L. Gross, J. Lupton, and J. Repp
(See online at https://doi.org/10.1126/science.abh1155) - Exploiting Cooperative Catalysis for the On-surface Synthesis of Linear Heteroaromatic Polymers via Selective C-H Activation. Angewandte Chemie International Edition 61, e202112798 (2021)
X. Liu, A. Matej, T. Kratky, J. Mendieta-Moreno, S. Günther, P. Mutombo, S. Decurtins, U. Aschauer, J. Repp, P. Jelinek, S. X. Liu, and L. Patera
(See online at https://doi.org/10.1002/anie.202112798) - Towards atomically controlled on-surface chemistry on insulating surfaces. PhD thesis, University of Regensburg (2021)
Sophia Sokolov
(See online at https://doi.org/10.5283/epub.51946)
