Chemistry & Light Research Theme Seminar

A very important axis of research in organic and coordination chemistry is the development of molecular materials for their use in renewable energy production using sun light. Two major avenues are organic or hybrid photo-voltaics and photo-catalytic hydrogen production, and the functional photo-chemical processes involved are charge transfer, energy transfer or singlet fission. The molecular materials design parameters are the amplitude and spectral widths of their extinction spectra, but also the reaction rates of the above processes since their quantum efficiencies are in general a result of kinetic competition between productive and non-productive photo-chemistry. Hence, ultrafast spectroscopy is naturally a wide-spread and very versatile tool to study the functional photo-chemical processes and how they are affected by the molecular design. In this talk, we will report on two distinct topics where femtosecond transient absorption and fluorescence spectroscopy allowed us to provide a detailed insight into the excited state reactions. The first is the development of near-IR absorbing pyrrolopyrrol cyanine dyes for semi-transparent dye-sensitised solar cells [1]. The second deals with turning Fe(II) metal-organic complexes into photo-sensitisers, with the long-term aim being to replace expensive and rare transition metals like Pt, Ru or Ir by earth-abundant congeners. Here femtosecond optical spectroscopy comes to its limits [2], but vibrational spectroscopy turns out to provide key information about the complex excited relaxation pathways [3].

[1] T. Baron et al. Angew. Chem. Int. Ed., 61, e202207459 (2022)

[2] C. Cebrian et al., ChemPhysChem, 23, e202100659 (2022)

[3] F. Hainer et al., J. Chem. Phys. Lett., 12, 8560-8565 (2021)