Spectroscopic Investigation of Ground State Charge Transfer in Organic Mixed-valence and Charge-transfer Systems

Open Access
Author:
Bischof, Angela Maria
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 10, 2015
Committee Members:
  • Benjamin James Lear, Dissertation Advisor
  • Thomas E Mallouk, Committee Member
  • Miriam Arak Freedman, Committee Member
  • Li Li, Special Member
Keywords:
  • organic mixed-valence
  • organic charge-transfer
  • electron transfer
Abstract:
Electron transfer processes are widespread in chemistry, and form the basis of photosynthetic systems and molecular electronic devices. However, studying electron transfer processes in these systems directly can be difficult. In order to understand the fundamental processes in these systems, charge transfer (CT) and mixed-valence (MV) compounds have been used extensively as model systems to study the basics of electron transfer reactions under various conditions. This dissertation uses steady-state spectroscopic analyses to determine how structure affects electronic coupling and charge delocalization in several MV and CT systems that are of interest for understanding the fundamental processes that occur in organic devices. In Chapter 2, we find that the introduction of an ethylene bridging ligand between two bis(alkoxy)benzene redox sites increases the intramolecular electronic coupling when compared to the system in which the redox active sites are directly connected, despite an increase in distance. We quantify the increase in coupling as a function of both distance and steric effects. Chapter 3 focuses on the systematic investigation of how van der Waals forces control the electronic coupling in non-covalently bound organic mixed-valence naphthalene diimide dimers, and we find that, in general, as the van der Waals forces in the intermolecular complex increase so does the electronic coupling. Chapter 4 focuses on the analysis of the CT band in donor-acceptor charge-transfer liquid crystals (DACLCs) and uses resonance Raman spectroscopy to investigate the phase-dependence of the charge transfer transition and the vibrational modes that are associated with this transition. Overall, this dissertation contributes to the fundamental understanding of how structure impacts charge transfer in organic MV and CT systems.