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

• Published in: The journal of physical chemistry letters 2021-01, Vol.12 (4)
• Main Authors: Cordones, Amy A., Pemmaraju, C. Das, Lee, Jae Hyuk, Zegkinoglou, Ioannis, Ragoussi, Maria-Eleni, Himpsel, Franz J., de la Torre, Gema, Schoenlein, Robert W.
• Format: Article
• Language: English
• Subjects: absorption; absorption spectroscopy; excited states; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; macrocycles; pyrroles
• ISSN: 1948-7185; 1948-7185

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. Furthermore, 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.