Periodic Reporting for period 1 - PRETZEL (Dynamics of photoinduced resonant energy transfer characterized at the single molecule level.)
Reporting period: 2020-05-01 to 2022-04-30
Mechanisms such as light absorption, excitation and energy transfer, crucial e.g. for photosynthesis, are usually probed by ensemble-averaging methods obscuring atomic-scale properties. This project aimed at tackling this issue by developing and employing a novel approach: a combination of an atomically-precise scanning tunnelling microscope and an all-optical method providing temporal resolution. Profiting from the opportunities provided by the atomic-scale optics, PRETZEL focused on understanding light-matter interaction, in particular the energy transfer process at the level of individual chromophores and multimolecular assemblies. In such systems, the chemical nature, distance and dipole orientation, as well as coupling to the local electromagnetic fields can be precisely controlled.
In the course of the project, we have developed a unique experimental set-up that enables energy- and time-resolved optical excitation of individual molecules in the tunnel junction. Several technical challenges, including laser alignment and sufficient tip quality, have been solved on the way toward successful detection of photoluminescence from a single chromophore.
In addition to the experimental advances, the project succeeded in probing several crucial aspects of light-matter interaction at the scale of individual molecules. Their excitation was efficiently controlled by adapting the energy of the incoming radiation, which also affects the chemical properties of the studied molecule. On the other hand, the emission dynamics of such emitters are affected by the presence of plasmon-enhanced electromagnetic fields. The spectral characteristics of the emission indicate excited-state lifetimes on the order of 1 picosecond. Such short excitation lifetimes indicate that the energy transfer dynamics are on the same order. This process was studied using more complex systems, consisting of molecular dimers and trimers.
Parts of these research achievements were published and presented at international conferences already during the action.
In addition to the experimental advances, the project succeeded in probing several crucial aspects of light-matter interaction at the scale of individual molecules. Their excitation was efficiently controlled by adapting the energy of the incoming radiation, which also affects the chemical properties of the studied molecule. On the other hand, the emission dynamics of such emitters are affected by the presence of plasmon-enhanced electromagnetic fields. The spectral characteristics of the emission indicate excited-state lifetimes on the order of 1 picosecond. Such short excitation lifetimes indicate that the energy transfer dynamics are on the same order. This process was studied using more complex systems, consisting of molecular dimers and trimers.
Parts of these research achievements were published and presented at international conferences already during the action.
Achieving such control over energy transfer and developing a toy model system for such studies is critical for the further development of efficient light-harvesting materials. This is enabled only by properly understanding the physical mechanisms responsible for the light collection and the energy transport at the ultimate single-molecule level.