Multi-Spin Interactions and Dynamics in Model Systems for Organic Molecular Materials

This thesis presents results from the application of electron paramagnetic resonance (EPR) techniques to study the spin-spin interactions of novel organic compounds possessing one or more unpaired electron spins. The first two chapters focus on the use of steady-state techniques to probe the interaction of a single unpaired electron with its surrounding environment. The second part of this thesis expands on these studies by employing transient techniques to analyze and control the spin-spin interactions and dynamics of systems which undergo photoinduced charge separation to generate multiple unpaired electrons.;In Chapter 2 a series of novel trifluoromethylated perylene and naphthalene imide and diimide compounds are chemically reduced to yield their respective radical anions. EPR spectroscopy at both X-band and W-band fields allows for characterization of the hyperfine coupling constants and g-tensors which are important for studying their role as intermediates in electron transfer reactions. In Chapter 3 continuous-wave electron-nuclear double resonance (ENDOR) spectroscopy is employed to study the sharing of an unpaired electron across oligomers of naphthalene-1,8:4,5-bis(dicarboximide) in several novel geometries.;Transient EPR techniques are introduced in Chapter 4 to measure the spin-spin interactions in photogenerated radical pairs in a series of electron donor-acceptor systems designed to mimic the photosynthetic reaction center. Measurement of the dipolar interaction at X-band fields allows for the determination of the radical pair distance, while the enhanced spectral resolution at W-band fields allows for analysis of the anisotropy of the g-tensors thereby allowing for the determination of the geometry of the radical pair.;In Chapter 5 a novel U-shaped electron donor-acceptor-radical system is introduced in which use of a xanthene spacer results in negligible magnetic exchange interactions between the acceptor radical anion and the appended stable radical while the short through-space distance results in a strong ferromagnetic dipolar interaction leading to unique spectral features in the transient EPR spectra. In contrast, Chapter 6 is focused on a linear electron donor-acceptor-radical system in which magnetic exchange results in polarization of the appended radical spin which is then transferred to neighboring nuclear spins through the use of pulse ENDOR sequences thereby opening possibilities for a nuclear spin memory.