Exciton interaction in ultrafast spectroscopy

Ultrafast visible spectroscopy studies electronic states and their photoinduced dynamics. A prominent example is energy transfer in both natural photosynthetic complexes and artificial solar materials. Traditionally, the dynamics of a single excitation is followed by its transient spectrum. By this approach, long-range transport of single excitations in an iso-energetic landscape cannot be tracked, since the spectrum does not change. This is a severe limitation in larger systems such as photosynthetic supercomplexes or conjugated polymers. At the same time, the presence of multiple excitations presents an obstacle, since their interaction distorts the single-exciton signals. Recently, approaches by us and other groups appear to use highly nonlinear transient spectroscopy and allow isolation of the multi-excitonic signals. This provides not only access to single-excitation dynamics, but, utilizing the interaction, to long-range transport as well. This PhD project is concerned with the description of the multi-excitonic states: their properties, exciton–exciton interaction, signatures in time-resolved spectroscopy, and implications for the function of the relevant materials. The candidate will have the opportunity to collaborate with world-leading research groups of prof. Tobias Brixner, University of Wuerzburg, and Prof. Jacob J. Krich, University of Ottawa, that developed and apply the nonlinear spectroscopy methods, taking part in the development of this novel, exciting direction in ultrafast spectroscopy.

References:

Malý et al., „Separating single- from multi-particle dynamics in nonlinear spectroscopy“, Nature 616, 280 (2023)

Luettig et al., „Higher-Order Multidimensional and Pump–Probe Spectroscopies“, J. Phys. Chem. Lett. 14, 7556 (2023)

Malý et al., „From wavelike to sub-diffusive motion: exciton dynamics and interaction in squaraine copolymers of varying length“, Chem. Sci. 11, 456 (2020)