Abstract
Transition metal complexes (TMC) are ubiquitous in nature and pose remarkable electronic properties that have found use in artificial photosynthesis, photovoltaics, phototherapy and molecular electronics. Many of these applications are based on the interaction of TMC with light. Optical excitation triggers an electronic population relaxation cascade which could span several electronvolt on the time scale of a few tens of femtoseconds (1 fs = 10-15 s). It involves many transient intermediates accessible via competing channels in which the electron density oscillates between the central metal and the ligands. These primary steps after the interaction with light are of key importance as they determine the response of the system, but so far they have hardly been explored due to the lack of experimental tools with enough time resolution and accurate theoretical methods. ASTRAL aims to push ultrafast spectroscopy and theoretical modeling significantly beyond the state-of-the-art in order to identify the primary processes governing TMC in the first few femtoseconds upon UV photo-excitation. From an experimental point of view, we will develop a unique beamline for time-resolved X-ray absorption near-edge structure (tr-XANES) spectroscopy with unprecedented temporal resolution (<5 fs) and spectral pump tunability (200-450 nm). On the theoretical side, we will provide for the first time a general protocol for computing spectroscopy of TMC on top of short-time multidimensional quantum dynamics driven by Hamiltonians parametrized with novel multireference methods. This protocol will facilitate transient absorption spectroscopy simulations with probe pulses ranging from the Visible to the hard X-ray regime, allowing for an unambiguous interpretation of the experimental data. The beamline and protocol will be applied to study the ultrafast (sub-100 fs) internal conversion in metallo porphyrins and iridium complexes providing answers to the following scientific questions: • which is the dominant process during the sub-100 fs relxation in metalloporphyrins: ligand-centered internal conversion or ring-to-metal charge transfer? • what is the role of ligand- and metal-centered short-lived intermediates? • what are the mechanisms by which iridiumcomplexes relax from the UV absorbing singlet ligand-centered state to the lowest triplet metal-to-ligand charge-transfer state? • what makes vibrational redistribution on a sub-vibrational timescale so efficient?
Project details
Unibo Team Leader: Artur Nenov
Unibo involved Department/s:
Dipartimento di Chimica Industriale "Toso Montanari"
Coordinator:
CNR - Consiglio Nazionale delle Ricerche(Italy)
Total Unibo Contribution: Euro (EUR) 86.629,00
Project Duration in months: 24
Start Date:
28/09/2023
End Date:
27/09/2025
