Intramolecular electron transfer in mixed-valence triarylamines

Mixed-valence compounds are of interest as model systems for the study of electron transfer reactions. In Chapter 1, we find that the intramolecular electron transfer processes and patterns of charge delocalization in such compounds depend on the interplay between the electronic ( V) and the vibronic (lambda) coupling. One can obtain both parameters from a Hush analysis of the intervalence band that arises upon optical intramolecular electron transfer if the band is intense and well-separated from other bands. This is quite often the case for mixed-valence triarylamines. As such, both Hush analysis and simulation of the intervalence band are widely used to classify these types of compounds as charge localized (class-II) or delocalized (class-III). Yet one must estimate the diabatic electron transfer distance (R) to calculate V in the Hush formalism. For mixed-valence triarylamines, R is commonly taken as the N--N distance; Chapters 3 and 4 show this to be a poor approximation in many cases.;In Chapter 2, we find that the activation barrier to thermal intramolecular electron transfer in a class-II mixed-valence compound is also related to the parameters V and lambda. Thus, if one can capture the rate of thermal electron transfer at multiple temperatures, then two experimental methods exist by which to extract V and lambda. One technique that is widely used for organic mixed-valence compounds is variable-temperature electron spin resonance (ESR) spectroscopy. This method is only rarely used to determine thermal electron transfer rates in mixed-valence triarylamines, though, as the electron transfer in most of the class-II compounds is too fast to observe on the ESR timescale. Chapters 4 and 5 show, for the first time, that one can use ESR spectroscopy to measure thermal electron transfer rates in mixed-valence triarylamines for which an intervalence band is also observable. Simulation of ESR spectra based on density functional theory calculations and comparison with optical data can also uncover the nature (i.e., adiabatic or nonadiabatic) of the electron transfer process.;While Chapters 1 and 2 introduce the theory behind the two intramolecular electron transfer pathways in mixed-valence compounds, and Chapters 3-5 show that one can observe and correlate optical and thermal electron transfer in certain two- and three-center triarylamines, Chapter 6 is largely an outlook chapter. There, we find that two types of intervalence states can coexist within a single molecule. It is also this final chapter which shows that the concept of bridge energy and its effect on electronic coupling can reconcile the central results of the thesis.;The reader shall find a large amount of experimental data in the chapters to follow. The author does not intend to imply that any of this work is her own. Indeed, most of the data in Chapters 3-5 are the work of Dr. Susan Odom, Dr. Simon Jones and Dr. Stephen Barlow. Dr. Susan Odom, in particular, characterized the thiophene-based compounds and recorded most of the ESR spectra. The experimental data in Chapter 6 is culled from the literature. The main contribution of the author is not in the collection of data, but rather in the interpretation of the data from a theoretical viewpoint. It was the synergy between experiment and theory that led to the most important contributions of this thesis, and so both are given weight here.