Speaker
Description
At the heart of any light-harvesting technology, such as artificial photosynthesis or photovoltaics, lie the fundamental steps of photoinduced charge transfer and separation, which are best optimized by combining electron donor and acceptor materials into molecular dyads. In these architectures, the donor and acceptor units are integrated into a single molecule and linked by a π-conjugated moiety that facilitates intramolecular charge transfer (ICT) [1], where achieving high efficiency requires fast and efficient charge transfer with slow charge recombination to maintain the charge-separated state. Our approach focuses on the study of organic dyads based on the π-extended tetrathiafulvalene (exTTF) donor [2], a remarkable unit widely recognized for its applications in molecular electronics and solar energy conversion [3,4], linked to various nitrogen-containing acceptor groups to modulate the system's electronic dynamics. Our primary interest lies in fundamentally understanding how this charge separation occurs, and we therefore aim to track this phenomenon directly. We selected exTTF-based dyads due to their excellent electron-donating properties, as well as the presence of sulfur atoms within the exTTF core. The sulfur K-edfe can be easily probed using X-Ray Free electron Lasers (XFELs), enabling us to monitor the charge transfer process in real time. By employing X-ray Transient Absorption Spectroscopy (XTAS) at the SwissFEL facility of the Paul Scherrer Institut, we demonstrate the ability to track simultaneous oxidation and reduction processes with atomic-level precision by specifically monitoring the electronic environment of the sulfur centers. This element-specific approach provides a direct, real-time report on the electronic evolution of the system, showcasing the viability of tracking ultrafast redox dynamics in complex functional materials.