Capturing the first steps of electron transfer in organic molecules
The ultrafast redistribution of energy and electron charge in molecules after they absorb light may sound too scientific to be relevant to us in our everyday lives. However, it is this process that governs photosynthesis in plants and bacteria. It is also the driving mechanism in systems such as solar panels, where light is transformed into electricity. Being able to measure the electron and charge transfer dynamics of this phenomenon with extreme temporal resolution could help scientists understand the mechanics behind these processes. It could also provide valuable information on how to engineer a molecule’s properties in order to control or enhance them. However, detailed knowledge of the first steps involved in electron and charge transfer after prompt photoionisation has been lacking. Lacking, that is, until recently.
A new look at electron-nucleus interplay
Research supported by the EU-funded TOMATTO and LASERLAB-EUROPE projects has now led to new insight into this phenomenon. As described in a study published in ‘Nature Chemistry’, the team used attosecond (10-18 second) extreme-ultraviolet pulses to shed new light on the ultrafast dynamics of molecular systems. “This pioneering work offers a fresh perspective on the complex interplay between electrons and nuclei in donor-acceptor molecules, significantly advancing our understanding of chemical processes at the most fundamental level,” reports a news item posted on the TOMATTO website. For the purposes of their research, the team exposed nitroaniline molecules to attosecond pulses. This enabled them to observe and analyse the first stages of charge transfer with unparalleled precision. The research revealed that the transfer of electrons from the electron donor amino group took less than 10 femtoseconds (where a femtosecond is equal to 10-15 of a second) and was driven by a synchronised movement of nuclei and electrons. This was followed by a relaxation process that took place over a sub-30-femtosecond timescale as the nuclear wave packet spread in the excited electronic states of the molecular cation. The news item states: “The results reported here answer a fundamental question in chemistry as they unveil the times required to transfer charge from an electron donor unit to the adjacent chemical bond connecting that unit with a benzene ring, and for the concomitant required structural changes that occur. The authors believe that these experimental and theoretical findings pave the way to a better understanding of the textbook diagrams and concepts used to qualitatively predict charge migration in organic molecules.” The study supported by TOMATTO (The ultimate Time scale in Organic Molecular opto-electronics, the ATTOsecond) and LASERLAB-EUROPE (The Integrated Initiative of European Laser Research Infrastructures) therefore not only deepens scientific insight into molecular dynamics, it also paves the way for future advancements in attosecond physics. For more information, please see: TOMATTO project website LASERLAB-EUROPE project website
Keywords
TOMATTO, LASERLAB-EUROPE, molecule, electron, charge, transfer, transfer charge