In solar energy conversion ranging from artificial photosynthesis to photocatalysis, transition metal complexes (TMC) are essential building blocks due to several attractive properties: intense absorption within the solar spectrum, presence of charge-transfer excited state, and substrate binding capability through coordination geometry changes. In order to gain insight into controlling solar energy conversion processes, it is essential to acquire in-depth understanding of the structural dynamics of these complexes in their excited states. Upon light absorption, the TMCs undergo photophysical and photochemical processes that fundamentally dictate their overall functionality. The electronic and nuclear rearrangements involved in these processes are crucial pieces of information in realizing the overall function of the TMCs, and this can be accomplished with X-ray Transient Absorption (XTA) spectroscopy. XTA is a powerful technique that directly probes the metal center, revealing information about metal oxidation state, metal-centered electron configuration and orbital energies, and coordination geometry of the metal center in both ground and excited states of TMCs. The first portion of this work presents the excited state dynamics of Nickel phthalocyanine complex with eight butoxy substituents (NiPcOBu8). Using XTA based on synchrotron source, the 500-ps lived photoexcited state was assigned to the metal-centered Ni 1,3(3dz2, 3dx2-y2) state. NiPcOBu8 displays distinct 3d orbital levels and peak widths due to the inherently different structure of phthalocyanine macrocycle. The second portion deals with the investigation of photoinduced axial ligation process in NiPcOBu8. Although the phthalocyanine has been known to not for 6-coordinate structure, the XTA has revealed that NiPcOBu8 ligates with pyridine molecules in its excited state, with very distinctive ligation dynamics in contrast to Nickel porphyrin ligations. The third portion of this work involves photoinduced dynamics and structures of heteroleptic Copper(I) bis-phenanthroline complexes, which are promising candidate for the chromophore and catalyst in solar energy conversion architecture. By using XTA and optical transient absorption spectroscopy, the ligand substituent effect on the ground and excited states of the Cu complexes have been investigated. Finally, in the last portion of this work, the structural investigation of the highly active Iridium water oxidation catalyst using X-ray absorption and X-ray scattering methods is discussed.

Creator

• Hong, Jiyun

DOI

• https://doi.org/10.21985/n2-d2eq-6086

Subject

• Physical chemistry

Language

• en

Alternate Identifier

• etdadmin_upload_662106
• http://dissertations.umi.com/northwestern:14629

Keyword

• Transition Metal Complex
• Excited state dynamics
• X-ray Transient Absorption Spectroscopy

Date created

• 2019-01-01

Resource type

• Dissertation

Rights statement

• In Copyright