Using X-ray scattering and transient absorption to probe global and local structural dynamics of the bimetallic photocatalyst [Ir2(dimen)4]+2

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Mechanistic pathways of inorganic homogeneous catalyts are determined not only by the reactive electronic structure but also the precise arrangement of the atoms within the catalyst. Furthermore, without knowing precisely how nuclear structure and electronic structure affect each other, computational methods may not be able to accurately portray the behavior of certain inorganic complexes. Ir2(dimen)4{+2} (dimen = 1,8-diisocyano-p-menthane) is such a system. X-ray crystallography has long supposed that this particular d8-d8 dimer has two thermally accessible minima on the same ground state and more recent temperature dependent solution spectra support this but, so far, computational efforts have not been able to recreate a double minimum potential energy surface. However, a simple quasi-empirical mechanical spring model has been proposed in the literature which features two minima with a shallow barrier. Herein, a combination of transient absorption (TA) and time-resolved X-ray diffuse scattering (XDS) is used to determine that the potential energy surfaces of ground and excited state follow this model. When exciting extremes of the HOMO-LUMO band which have been inferred to correspond to each ground state minima, we are able to use vibrational wavepacket analysis to qualitatively confirm that the ground state possesses two minima while the excited state has only one, as predicted in the literature model. Furthermore, we are able to observe ground state interconversion in real-time, occuring the in ~10ps regime, confirming that interconversion is thermally accessible but with a barrier height over five times larger than predicted. Furthermore, a combination of XDS and Born-Oppenheimer Molecular Dynamics is used to produce a global picture of Ir2(dimen)4{+2} in solution in which a detailed molecular solvent response is characterized for the excited state. Using this approach, it was found, both computationally and experimentally, that he methyl groups prefer to coordinate to the ground state and recoordinate via the nitrile group in the excited state which is quite unexpected and could not be predicted by continuum models or electrostatic arguments.


Type of resource text
Form electronic; electronic resource; remote
Extent 1 online resource.
Publication date 2017
Issuance monographic
Language English


Associated with Hartsock, Robert W
Associated with Stanford University, Department of Chemistry.
Primary advisor Gaffney, Kelly
Thesis advisor Gaffney, Kelly
Thesis advisor Bucksbaum, Philip H
Thesis advisor Fayer, Michael D
Advisor Bucksbaum, Philip H
Advisor Fayer, Michael D


Genre Theses

Bibliographic information

Statement of responsibility Robert W. Hartsock.
Note Submitted to the Department of Chemistry.
Thesis Thesis (Ph.D.)--Stanford University, 2017.
Location electronic resource

Access conditions

© 2017 by Robert Walker Hartsock
This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).

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