Excitonic states play important roles in solar energy conversion for natural and artificial photosynthetic complexes and organic photovoltaics. However, investigation of the exciton states in these systems can be challenging due to structural complexity. Many molecules are found in different environments leading to a heterogeneous distribution of structures and transition frequencies. To overcome this issue researchers have turned to structurally simpler model systems. In this study, we investigate π-extended zinc dipyrrin complexes as model excitonic systems. While the ligands of many homoleptic zinc dipyrrin complexes have an orthogonal geometry, the homoleptic zinc π-extended dipyrrin complexes studied here have a non-orthogonal geometry resulting in a non-zero electronic coupling between the two identical dipyrrin ligands[1]. Applying 2DES to 1 in toluene we further investigate the formation of excitonic states in this system. Slices taken along the diagonal of the 2DES spectrum resolve additional spectral features compared to the linear spectra, as the diagonal peaks in the 2DES spectra scale as μ4. Comparing the diagonal slice from the 2DES spectrum with the linear spectrum and stick spectrum simulated with the Holstein Hamiltonian confirms the formation of excitonic states in 1.

Two-dimensional electronic spectroscopy of zinc π-extended dipyrrin complexes

ACS Fall 2020 Virtual Meeting

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