Ultrafast photophysics of transition metal coordination complexes studied with femtosecond extreme ultraviolet transient absorption spectroscopy

Photophysics;ultrafast spectroscopy;XANES;HHG spectroscopy;high-harmonic generation;tabletop XUV;instrumentation;X-ray spectroscopy;visible light spectroscopy;metalloporphyrin;coordination complex, ,

Ryland, Elizabeth S.

关键词: Photophysics;    ultrafast spectroscopy;    XANES;    HHG spectroscopy;    high-harmonic generation;    tabletop XUV;    instrumentation;    X-ray spectroscopy;    visible light spectroscopy;    metalloporphyrin;    coordination complex, ,;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/105598/RYLAND-DISSERTATION-2019.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Ultrafast femtosecond dynamics of various simple metalloporphryinates (M = Fe3+, Ni2+, Mn3+, Co2+) and a heterobimetallic complex CoMnCl(py3tren) are studied using a homebuilt extreme ultraviolet (XUV) transient absorption apparatus. XUV photons are produced via high-harmonic generation, allowing M-edge XANES measurements to be performed as an in-lab technique. This developing technique is coupled with semi-empirical ligand field multiplet (LFM) simulations to enable the application of tabletop M-edge XANES to resolve the metal-specific ultrafast relaxation mechanism of coordination complexes, complementing information gained from ligand-specific techniques such as optical transient absorption. The experimental apparatus for transient absorption pump-probe XANES of molecular thin films is described in detail. The research described in this thesis establishes M-edge spectroscopy as a powerful tool for studying the steady-state and transient electronic structure of coordination complexes. This technique has been applied to four metalloporphyrinates (FeTPPCl, NiOEP, CoOEP, and MnOEPCl); results show diverse M-edge transient spectra and kinetics that reveal the strong impact of the metal d-orbital occupation on the early time relaxation mechanism and intermediate states of these catalytically-relevant systems. This project is the first instance of using tabletop transient XUV/VUV spectroscopy on coordination complexes and furthermore highlights the importance of directly probing of the metal center in these systems. Ongoing work on the transient XANES of heterobimetallic complex CoMnCl(py3tren) (triply-deprotonated N,N,N-tri(2-(2-pyridylamino)ethyl)amine) is presented, the aim of which is to detangle the complex photophysics present in a system with directly-interacting dual metal centers within a non-innocent ligand scaffold. The relation of function to metal-specific photodynamics will help lay essential groundwork for the development of multimetallic catalysts with efficiencies comparable to those found in nature.