"Excited-State Charge Distribution of a Donor−π–Acceptor Zn Porphyrin Probed by N K-Edge Transient Absorption Spectroscopy"

Amy A. Cordones : C. Das Pemmaraju, Robert W. Schoenlein, Jae Hyuk Lee, Ioannis Zegkinoglou, Maria-Eleni Ragoussi, Franz J. Himpsel, Gema de la Torre ; The Journal of Physical Chemistry Letters, 01/22/21.

Additional Authors: C. Das Pemmaraju, Robert W. Schoenlein, Jae Hyuk Lee, Ioannis Zegkinoglou, Maria-Eleni Ragoussi, Franz J. Himpsel, Gema de la Torre

Abstract:

Zinc porphyrin solar cell dyes with donor−π–acceptor architectures combine light absorber (π), electron-donor, and electron-acceptor moieties inside a single molecule with atomic precision. The donor−π–acceptor design promotes the separation of charge carriers following optical excitation. Here, we probe the excited-state electronic structure within such molecules by combining time-resolved X-ray absorption spectroscopy at the N K-edge with first-principles time-dependent density functional theory (TD-DFT) calculations. Customized Zn porphyrins with strong-donor triphenylamine groups or weak-donor tri-tert-butylbenzene groups were synthesized. Energetically well-separated N K-edge absorption features simultaneously probe the excited-state electronic structure from the perspectives of the macrocycle and triphenylamine N atoms. New absorption transitions between the macrocycle N atoms and the excited-state HOMO vacancy are observed, and the triphenylamine associated absorption feature blue-shifts, consistent with partial oxidation of the donor groups in the excited state.

 

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