Dr. Alexander Eisfeld
MPI Komplexe Systeme Dresden
spricht zum Thema
Near-field optical spectroscopy of molecular assemblies
Abstract:
Assemblies of molecules (so-called molecular aggregates) have become versatile quantum systems with applications in photography, opto-electronics, solar cells, and photo-biology. The remarkable properties of these aggregates stem from the strong transition dipole-dipole interaction between the individual molecules which leads to eigenstates with excitation shared coherently by a large number of molecules. As a consequence the aggregate possesses strikingly different optical properties compared to the individual molecules. Knowledge about these delocalized eigenstates is not only important to understand the optical properties but also to understand and design the transfer of electronic excitation. Optical spectroscopy, in principle, allows one to infer information on these eigenstates and about the interactions between the molecules. However, traditional optical techniques using an electromagnetic field which is uniform over the relevant size of the aggregate cannot access most of the excited states because of selection rules. I will show that by using localized fields one can obtain information about these otherwise inaccessible states. As an example, we discuss in detail the case of local excitation via radiation from the apex of a metallic tip, which allows also scanning across the aggregate. The resulting spatially resolved spectra allow in principle to obtain the eigenenergies and wave functions.
[1] Gao, Eisfeld; J. Phys. Chem. Lett. 9 (2018) 6003
[2] Zheng, Gao, Eisfeld; Phy. Rev. Lett. 123 (2019) 163202
[3] Nayak, Zheng, Eisfeld; J. Chem. Phys. 155 (2021) 134701
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